| Message ID | 20220628194812.1453059-1-alexandr.lobakin@intel.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | bpf, xdp: introduce and use Generic Hints/metadata | expand |
Alexander Lobakin wrote: > This RFC is to give the whole picture. It will most likely be split > onto several series, maybe even merge cycles. See the "table of > contents" below. Even for RFC its a bit much. Probably improve the summary message here as well I'm still not clear on the overall architecture so not sure I want to dig into patches. > > The series adds ability to pass different frame > details/parameters/parameters used by most of NICs and the kernel > stack (in skbs), not essential, but highly wanted, such as: > > * checksum value, status (Rx) or command (Tx); > * hash value and type/level (Rx); > * queue number (Rx); > * timestamps; > * and so on. > > As XDP structures used to represent frames are as small as possible > and must stay like that, it is done by using the already existing > concept of metadata, i.e. some space right before a frame where BPF > programs can put arbitrary data. OK so you stick attributes in the metadata. You can do this without touching anything but your driver today. Why not push a patch to ice to start doing this? People could start using it today and put it in some feature flag. I get everyone wants some grand theory around this but again one patch would do it and your customers could start using it. Show a benchmark with 20% speedup or whatever with small XDP prog update and you win. > > Now, a NIC driver, or even a SmartNIC itself, can put those params > there in a well-defined format. The format is fixed, but can be of > several different types represented by structures, which definitions > are available to the kernel, BPF programs and the userland. I don't think in general the format needs to be fixed. > It is fixed due to it being almost a UAPI, and the exact format can > be determined by reading the last 10 bytes of metadata. They contain > a 2-byte magic ID to not confuse it with a non-compatible meta and > a 8-byte combined BTF ID + type ID: the ID of the BTF where this > structure is defined and the ID of that definition inside that BTF. > Users can obtain BTF IDs by structure types using helpers available > in the kernel, BPF (written by the CO-RE/verifier) and the userland > (libbpf -> kernel call) and then rely on those ID when reading data > to make sure whether they support it and what to do with it. > Why separate magic and ID? The idea is to make different formats > always contain the basic/"generic" structure embedded at the end. > This way we can still benefit in purely generic consumers (like > cpumap) while providing some "extra" data to those who support it. I don't follow this. If you have a struct in your driver name it something obvious, ice_xdp_metadata. If I understand things correctly just dump the BTF for the driver, extract the struct and done you can use CO-RE reads. For the 'fixed' case this looks easy. And I don't think you even need a patch for this. > > The enablement of this feature is controlled on attaching/replacing > XDP program on an interface with two new parameters: that combined > BTF+type ID and metadata threshold. > The threshold specifies the minimum frame size which a driver (or > NIC) should start composing metadata from. It is introduced instead > of just false/true flag due to that often it's not worth it to spend > cycles to fetch all that data for such small frames: let's say, it > can be even faster to just calculate checksums for them on CPU > rather than touch non-coherent DMA zone. Simple XDP_DROP case loses > 15 Mpps on 64 byte frames with enabled metadata, threshold can help > mitigate that. I would put this in the bonus category. Can you do the simple thing above without these extra bits and then add them later. Just pick some overly conservative threshold to start with. > > The RFC can be divided into 8 parts: I'm missing something why not do the simplest bit of work and get this running in ice with a few smallish driver updates so we can all see it. No need for so many patches. > > 01-04: BTF ID hacking: here Larysa provides BPF programs with not > only type ID, but the ID of the BTF as well by using the > unused upper 32 bits. > 05-10: this provides in-kernel mechanisms for taking ID and > threshold from the userspace and passing it to the drivers. > 11-18: provides libbpf API to be able to specify those params from > the userspace, plus some small selftest to verify that both > the kernel and the userspace parts work. > 19-29: here the actual structure is defined, then the in-kernel > helpers and finally here comes the first consumer: function > used to convert &xdp_frame to &sk_buff now will be trying > to parse metadata. The affected users are cpumap and veth. > 30-36: here I try to benefit from the metadata in cpumap even more > by switching it to GRO. Now that we have checksums from NIC > available... but even with no meta it gives some fair > improvements. > 37-43: enabling building generic metadata on Generic/skb path. Since > skbs already have all those fields, it's not a problem to do > this in here, plus allows to benefit from it on interfaces > not supporting meta yet. > 44-47: ice driver part, including enabling prog hot-swap; > 48-52: adds a complex selftest to verify everything works. Can be > used as a sample as well, showing how to work with metadata > in BPF programs and how to configure it from the userspace. > > Please refer to the actual commit messages where some precise > implementation details might be explained. > Nearly 20 of 52 are various cleanups and prereqs, as usually. > > Perf figures were taken on cpumap redirect from the ice interface > (driver-side XDP), redirecting the traffic within the same node. > > Frame size / 64/42 128/20 256/8 512/4 1024/2 1532/1 > thread num You'll have to remind me whats the production use case for cpu_map on a modern nic or even smart nic? Why are you not just using a hardware queues and redirecting to the right queues in hardware to start with? Also my understanding is if you do XDP_PASS up the stack the skb is built with all the normal good stuff from hw descriptor. Sorry going to need some extra context here to understand. Could you do a benchmark for AF_XDP I thought this was the troublesome use case where the user space ring lost the hardware info e.g. timestamps and checksum values. > > meta off 30022 31350 21993 12144 6374 3610 > meta on 33059 28502 21503 12146 6380 3610 > GRO meta off 30020 31822 21970 12145 6384 3610 > GRO meta on 34736 28848 21566 12144 6381 3610 > > Yes, redirect between the nodes plays awfully with the metadata > composed by the driver: Many production use case use XDP exactly for this. If it slows this basic use case down its going to be very hard to use in many environments. Likely it wont be used. > > meta off 21449 18078 16897 11820 6383 3610 > meta on 16956 19004 14337 8228 5683 2822 > GRO meta off 22539 19129 16304 11659 6381 3592 > GRO meta on 17047 20366 15435 8878 5600 2753 Do you have hardware that can write the data into the metadata region so you don't do it in software? Seems like it should be doable without much trouble and would make this more viable. > > Questions still open: > > * the actual generic structure: it must have all the fields used > oftenly and by the majority of NICs. It can always be expanded > later on (note that the structure grows to the left), but the > less often UAPI is modified, the better (less compat pain); I don't believe a generic structure is needed. > * ability to specify the exact fields to fill by the driver, e.g. > flags bitmap passed from the userspace. In theory it can be more > optimal to not spend cycles on data we don't need, but at the > same time increases the complexity of the whole concept (e.g. it > will be more problematic to unify drivers' routines for collecting > data from descriptors to metadata and to skbs); > * there was an idea to be able to specify from the userspace the > desired cacheline offset, so that [the wanted fields of] metadata > and the packet headers would lay in the same CL. Can't be > implemented in Generic/skb XDP and ice has some troubles with it > too; > * lacks AF_XDP/XSk perf numbers and different other scenarios in > general, is the current implementation optimal for them? AF_XDP is the primary use case from my understanding. > * metadata threshold and everything else present in this > implementation. I really think your asking questions that are two or three jumps away. Why not do the simplest bit first and kick the driver with an on/off switch into this mode. But I don't understand this cpumap use case so maybe explain that first. And sorry didn't even look at your 50+ patches. Figure lets get agreement on the goal first. .John
John Fastabend <john.fastabend@gmail.com> writes: > Alexander Lobakin wrote: >> This RFC is to give the whole picture. It will most likely be split >> onto several series, maybe even merge cycles. See the "table of >> contents" below. > > Even for RFC its a bit much. Probably improve the summary > message here as well I'm still not clear on the overall > architecture so not sure I want to dig into patches. +1 on this, and piggybacking on your comment to chime in on the general architecture. >> Now, a NIC driver, or even a SmartNIC itself, can put those params >> there in a well-defined format. The format is fixed, but can be of >> several different types represented by structures, which definitions >> are available to the kernel, BPF programs and the userland. > > I don't think in general the format needs to be fixed. No, that's the whole point of BTF: it's not supposed to be UAPI, we'll use CO-RE to enable dynamic formats... [...] >> It is fixed due to it being almost a UAPI, and the exact format can >> be determined by reading the last 10 bytes of metadata. They contain >> a 2-byte magic ID to not confuse it with a non-compatible meta and >> a 8-byte combined BTF ID + type ID: the ID of the BTF where this >> structure is defined and the ID of that definition inside that BTF. >> Users can obtain BTF IDs by structure types using helpers available >> in the kernel, BPF (written by the CO-RE/verifier) and the userland >> (libbpf -> kernel call) and then rely on those ID when reading data >> to make sure whether they support it and what to do with it. >> Why separate magic and ID? The idea is to make different formats >> always contain the basic/"generic" structure embedded at the end. >> This way we can still benefit in purely generic consumers (like >> cpumap) while providing some "extra" data to those who support it. > > I don't follow this. If you have a struct in your driver name it > something obvious, ice_xdp_metadata. If I understand things > correctly just dump the BTF for the driver, extract the > struct and done you can use CO-RE reads. For the 'fixed' case > this looks easy. And I don't think you even need a patch for this. ...however as we've discussed previously, we do need a bit of infrastructure around this. In particular, we need to embed the embed the BTF ID into the metadata itself so BPF can do runtime disambiguation between different formats (and add the right CO-RE primitives to make this easy). This is for two reasons: - The metadata might be different per-packet (e.g., PTP packets with timestamps interleaved with bulk data without them) - With redirects we may end up processing packets from different devices in a single XDP program (in devmap or cpumap, or on a veth) so we need to be able to disambiguate at runtime. So I think the part of the design that puts the BTF ID into the end of the metadata struct is sound; however, the actual format doesn't have to be fixed, we can use CO-RE to pick out the bits that a given BPF program needs; we just need a convention for how drivers report which format(s) they support. Which we should also agree on (and add core infrastructure around) so each driver doesn't go around inventing their own conventions. >> The enablement of this feature is controlled on attaching/replacing >> XDP program on an interface with two new parameters: that combined >> BTF+type ID and metadata threshold. >> The threshold specifies the minimum frame size which a driver (or >> NIC) should start composing metadata from. It is introduced instead >> of just false/true flag due to that often it's not worth it to spend >> cycles to fetch all that data for such small frames: let's say, it >> can be even faster to just calculate checksums for them on CPU >> rather than touch non-coherent DMA zone. Simple XDP_DROP case loses >> 15 Mpps on 64 byte frames with enabled metadata, threshold can help >> mitigate that. > > I would put this in the bonus category. Can you do the simple thing > above without these extra bits and then add them later. Just > pick some overly conservative threshold to start with. Yeah, I'd agree this kind of configuration is something that can be added later, and also it's sort of orthogonal to the consumption of the metadata itself. Also, tying this configuration into the loading of an XDP program is a terrible interface: these are hardware configuration options, let's just put them into ethtool or 'ip link' like any other piece of device configuration. >> The RFC can be divided into 8 parts: > > I'm missing something why not do the simplest bit of work and > get this running in ice with a few smallish driver updates > so we can all see it. No need for so many patches. Agreed. This incremental approach is basically what Jesper's simultaneous series makes a start on, AFAICT? Would be nice if y'all could converge the efforts :) [...] > I really think your asking questions that are two or three > jumps away. Why not do the simplest bit first and kick > the driver with an on/off switch into this mode. But > I don't understand this cpumap use case so maybe explain > that first. > > And sorry didn't even look at your 50+ patches. Figure lets > get agreement on the goal first. +1 on both of these :) -Toke
On Tue, Jun 28, 2022 at 11:15 PM John Fastabend <john.fastabend@gmail.com> wrote: > > Alexander Lobakin wrote: > > This RFC is to give the whole picture. It will most likely be split > > onto several series, maybe even merge cycles. See the "table of > > contents" below. > > Even for RFC its a bit much. Probably improve the summary > message here as well I'm still not clear on the overall > architecture so not sure I want to dig into patches. > > > > > The series adds ability to pass different frame > > details/parameters/parameters used by most of NICs and the kernel > > stack (in skbs), not essential, but highly wanted, such as: > > > > * checksum value, status (Rx) or command (Tx); > > * hash value and type/level (Rx); > > * queue number (Rx); > > * timestamps; > > * and so on. > > > > As XDP structures used to represent frames are as small as possible > > and must stay like that, it is done by using the already existing > > concept of metadata, i.e. some space right before a frame where BPF > > programs can put arbitrary data. > > OK so you stick attributes in the metadata. You can do this without > touching anything but your driver today. Why not push a patch to > ice to start doing this? People could start using it today and put > it in some feature flag. > > I get everyone wants some grand theory around this but again one > patch would do it and your customers could start using it. Show > a benchmark with 20% speedup or whatever with small XDP prog > update and you win. > > > > > Now, a NIC driver, or even a SmartNIC itself, can put those params > > there in a well-defined format. The format is fixed, but can be of > > several different types represented by structures, which definitions > > are available to the kernel, BPF programs and the userland. > > I don't think in general the format needs to be fixed. > > > It is fixed due to it being almost a UAPI, and the exact format can > > be determined by reading the last 10 bytes of metadata. They contain > > a 2-byte magic ID to not confuse it with a non-compatible meta and > > a 8-byte combined BTF ID + type ID: the ID of the BTF where this > > structure is defined and the ID of that definition inside that BTF. > > Users can obtain BTF IDs by structure types using helpers available > > in the kernel, BPF (written by the CO-RE/verifier) and the userland > > (libbpf -> kernel call) and then rely on those ID when reading data > > to make sure whether they support it and what to do with it. > > Why separate magic and ID? The idea is to make different formats > > always contain the basic/"generic" structure embedded at the end. > > This way we can still benefit in purely generic consumers (like > > cpumap) while providing some "extra" data to those who support it. > > I don't follow this. If you have a struct in your driver name it > something obvious, ice_xdp_metadata. If I understand things > correctly just dump the BTF for the driver, extract the > struct and done you can use CO-RE reads. For the 'fixed' case > this looks easy. And I don't think you even need a patch for this. > > > > > The enablement of this feature is controlled on attaching/replacing > > XDP program on an interface with two new parameters: that combined > > BTF+type ID and metadata threshold. > > The threshold specifies the minimum frame size which a driver (or > > NIC) should start composing metadata from. It is introduced instead > > of just false/true flag due to that often it's not worth it to spend > > cycles to fetch all that data for such small frames: let's say, it > > can be even faster to just calculate checksums for them on CPU > > rather than touch non-coherent DMA zone. Simple XDP_DROP case loses > > 15 Mpps on 64 byte frames with enabled metadata, threshold can help > > mitigate that. > > I would put this in the bonus category. Can you do the simple thing > above without these extra bits and then add them later. Just > pick some overly conservative threshold to start with. > > > > > The RFC can be divided into 8 parts: > > I'm missing something why not do the simplest bit of work and > get this running in ice with a few smallish driver updates > so we can all see it. No need for so many patches. > > > > > 01-04: BTF ID hacking: here Larysa provides BPF programs with not > > only type ID, but the ID of the BTF as well by using the > > unused upper 32 bits. > > 05-10: this provides in-kernel mechanisms for taking ID and > > threshold from the userspace and passing it to the drivers. > > 11-18: provides libbpf API to be able to specify those params from > > the userspace, plus some small selftest to verify that both > > the kernel and the userspace parts work. > > 19-29: here the actual structure is defined, then the in-kernel > > helpers and finally here comes the first consumer: function > > used to convert &xdp_frame to &sk_buff now will be trying > > to parse metadata. The affected users are cpumap and veth. > > 30-36: here I try to benefit from the metadata in cpumap even more > > by switching it to GRO. Now that we have checksums from NIC > > available... but even with no meta it gives some fair > > improvements. > > 37-43: enabling building generic metadata on Generic/skb path. Since > > skbs already have all those fields, it's not a problem to do > > this in here, plus allows to benefit from it on interfaces > > not supporting meta yet. > > 44-47: ice driver part, including enabling prog hot-swap; > > 48-52: adds a complex selftest to verify everything works. Can be > > used as a sample as well, showing how to work with metadata > > in BPF programs and how to configure it from the userspace. > > > > Please refer to the actual commit messages where some precise > > implementation details might be explained. > > Nearly 20 of 52 are various cleanups and prereqs, as usually. > > > > Perf figures were taken on cpumap redirect from the ice interface > > (driver-side XDP), redirecting the traffic within the same node. > > > > Frame size / 64/42 128/20 256/8 512/4 1024/2 1532/1 > > thread num > > You'll have to remind me whats the production use case for > cpu_map on a modern nic or even smart nic? Why are you not > just using a hardware queues and redirecting to the right > queues in hardware to start with? > > Also my understanding is if you do XDP_PASS up the stack > the skb is built with all the normal good stuff from hw > descriptor. Sorry going to need some extra context here > to understand. > > Could you do a benchmark for AF_XDP I thought this was > the troublesome use case where the user space ring lost > the hardware info e.g. timestamps and checksum values. > > > > > meta off 30022 31350 21993 12144 6374 3610 > > meta on 33059 28502 21503 12146 6380 3610 > > GRO meta off 30020 31822 21970 12145 6384 3610 > > GRO meta on 34736 28848 21566 12144 6381 3610 > > > > Yes, redirect between the nodes plays awfully with the metadata > > composed by the driver: > > Many production use case use XDP exactly for this. If it > slows this basic use case down its going to be very hard > to use in many environments. Likely it wont be used. > > > > > meta off 21449 18078 16897 11820 6383 3610 > > meta on 16956 19004 14337 8228 5683 2822 > > GRO meta off 22539 19129 16304 11659 6381 3592 > > GRO meta on 17047 20366 15435 8878 5600 2753 > > Do you have hardware that can write the data into the > metadata region so you don't do it in software? Seems > like it should be doable without much trouble and would > make this more viable. > > > > > Questions still open: > > > > * the actual generic structure: it must have all the fields used > > oftenly and by the majority of NICs. It can always be expanded > > later on (note that the structure grows to the left), but the > > less often UAPI is modified, the better (less compat pain); > > I don't believe a generic structure is needed. > > > * ability to specify the exact fields to fill by the driver, e.g. > > flags bitmap passed from the userspace. In theory it can be more > > optimal to not spend cycles on data we don't need, but at the > > same time increases the complexity of the whole concept (e.g. it > > will be more problematic to unify drivers' routines for collecting > > data from descriptors to metadata and to skbs); > > * there was an idea to be able to specify from the userspace the > > desired cacheline offset, so that [the wanted fields of] metadata > > and the packet headers would lay in the same CL. Can't be > > implemented in Generic/skb XDP and ice has some troubles with it > > too; > > * lacks AF_XDP/XSk perf numbers and different other scenarios in > > general, is the current implementation optimal for them? > > AF_XDP is the primary use case from my understanding. > AF_XDP is a use case, and might be the primary, but we work with pure XDP and have been waiting for the ability to take advantage of the hardware checksums for years. It would be a very large performance boost for us (in theory) as we're currently having to verify the checksums ourselves in software, and recompute them on modifications (since we can't use hardware TX checksums). Also, if I understand correctly, if the functionality is available to pure XDP, AF_XDP could benefit from it by having the XDP program that redirects to AF_XDP copy it into metadata where AF_XDP can find it because of the user defined contract between the XDP program and the userspace program? (Not as efficient, obviously, and duplicative, but would work, I think.) > > * metadata threshold and everything else present in this > > implementation. > > I really think your asking questions that are two or three > jumps away. Why not do the simplest bit first and kick > the driver with an on/off switch into this mode. But > I don't understand this cpumap use case so maybe explain > that first. > > And sorry didn't even look at your 50+ patches. Figure lets > get agreement on the goal first. > > .John
On Wed, Jun 29, 2022 at 7:57 PM Zvi Effron <zeffron@riotgames.com> wrote: > > On Tue, Jun 28, 2022 at 11:15 PM John Fastabend > <john.fastabend@gmail.com> wrote: > > > > Alexander Lobakin wrote: > > > This RFC is to give the whole picture. It will most likely be split > > > onto several series, maybe even merge cycles. See the "table of > > > contents" below. > > > > Even for RFC its a bit much. Probably improve the summary > > message here as well I'm still not clear on the overall > > architecture so not sure I want to dig into patches. > > > > > > > > The series adds ability to pass different frame > > > details/parameters/parameters used by most of NICs and the kernel > > > stack (in skbs), not essential, but highly wanted, such as: > > > > > > * checksum value, status (Rx) or command (Tx); > > > * hash value and type/level (Rx); > > > * queue number (Rx); > > > * timestamps; > > > * and so on. > > > > > > As XDP structures used to represent frames are as small as possible > > > and must stay like that, it is done by using the already existing > > > concept of metadata, i.e. some space right before a frame where BPF > > > programs can put arbitrary data. > > > > OK so you stick attributes in the metadata. You can do this without > > touching anything but your driver today. Why not push a patch to > > ice to start doing this? People could start using it today and put > > it in some feature flag. > > > > I get everyone wants some grand theory around this but again one > > patch would do it and your customers could start using it. Show > > a benchmark with 20% speedup or whatever with small XDP prog > > update and you win. > > > > > > > > Now, a NIC driver, or even a SmartNIC itself, can put those params > > > there in a well-defined format. The format is fixed, but can be of > > > several different types represented by structures, which definitions > > > are available to the kernel, BPF programs and the userland. > > > > I don't think in general the format needs to be fixed. > > > > > It is fixed due to it being almost a UAPI, and the exact format can > > > be determined by reading the last 10 bytes of metadata. They contain > > > a 2-byte magic ID to not confuse it with a non-compatible meta and > > > a 8-byte combined BTF ID + type ID: the ID of the BTF where this > > > structure is defined and the ID of that definition inside that BTF. > > > Users can obtain BTF IDs by structure types using helpers available > > > in the kernel, BPF (written by the CO-RE/verifier) and the userland > > > (libbpf -> kernel call) and then rely on those ID when reading data > > > to make sure whether they support it and what to do with it. > > > Why separate magic and ID? The idea is to make different formats > > > always contain the basic/"generic" structure embedded at the end. > > > This way we can still benefit in purely generic consumers (like > > > cpumap) while providing some "extra" data to those who support it. > > > > I don't follow this. If you have a struct in your driver name it > > something obvious, ice_xdp_metadata. If I understand things > > correctly just dump the BTF for the driver, extract the > > struct and done you can use CO-RE reads. For the 'fixed' case > > this looks easy. And I don't think you even need a patch for this. > > > > > > > > The enablement of this feature is controlled on attaching/replacing > > > XDP program on an interface with two new parameters: that combined > > > BTF+type ID and metadata threshold. > > > The threshold specifies the minimum frame size which a driver (or > > > NIC) should start composing metadata from. It is introduced instead > > > of just false/true flag due to that often it's not worth it to spend > > > cycles to fetch all that data for such small frames: let's say, it > > > can be even faster to just calculate checksums for them on CPU > > > rather than touch non-coherent DMA zone. Simple XDP_DROP case loses > > > 15 Mpps on 64 byte frames with enabled metadata, threshold can help > > > mitigate that. > > > > I would put this in the bonus category. Can you do the simple thing > > above without these extra bits and then add them later. Just > > pick some overly conservative threshold to start with. > > > > > > > > The RFC can be divided into 8 parts: > > > > I'm missing something why not do the simplest bit of work and > > get this running in ice with a few smallish driver updates > > so we can all see it. No need for so many patches. > > > > > > > > 01-04: BTF ID hacking: here Larysa provides BPF programs with not > > > only type ID, but the ID of the BTF as well by using the > > > unused upper 32 bits. > > > 05-10: this provides in-kernel mechanisms for taking ID and > > > threshold from the userspace and passing it to the drivers. > > > 11-18: provides libbpf API to be able to specify those params from > > > the userspace, plus some small selftest to verify that both > > > the kernel and the userspace parts work. > > > 19-29: here the actual structure is defined, then the in-kernel > > > helpers and finally here comes the first consumer: function > > > used to convert &xdp_frame to &sk_buff now will be trying > > > to parse metadata. The affected users are cpumap and veth. > > > 30-36: here I try to benefit from the metadata in cpumap even more > > > by switching it to GRO. Now that we have checksums from NIC > > > available... but even with no meta it gives some fair > > > improvements. > > > 37-43: enabling building generic metadata on Generic/skb path. Since > > > skbs already have all those fields, it's not a problem to do > > > this in here, plus allows to benefit from it on interfaces > > > not supporting meta yet. > > > 44-47: ice driver part, including enabling prog hot-swap; > > > 48-52: adds a complex selftest to verify everything works. Can be > > > used as a sample as well, showing how to work with metadata > > > in BPF programs and how to configure it from the userspace. > > > > > > Please refer to the actual commit messages where some precise > > > implementation details might be explained. > > > Nearly 20 of 52 are various cleanups and prereqs, as usually. > > > > > > Perf figures were taken on cpumap redirect from the ice interface > > > (driver-side XDP), redirecting the traffic within the same node. > > > > > > Frame size / 64/42 128/20 256/8 512/4 1024/2 1532/1 > > > thread num > > > > You'll have to remind me whats the production use case for > > cpu_map on a modern nic or even smart nic? Why are you not > > just using a hardware queues and redirecting to the right > > queues in hardware to start with? > > > > Also my understanding is if you do XDP_PASS up the stack > > the skb is built with all the normal good stuff from hw > > descriptor. Sorry going to need some extra context here > > to understand. > > > > Could you do a benchmark for AF_XDP I thought this was > > the troublesome use case where the user space ring lost > > the hardware info e.g. timestamps and checksum values. > > > > > > > > meta off 30022 31350 21993 12144 6374 3610 > > > meta on 33059 28502 21503 12146 6380 3610 > > > GRO meta off 30020 31822 21970 12145 6384 3610 > > > GRO meta on 34736 28848 21566 12144 6381 3610 > > > > > > Yes, redirect between the nodes plays awfully with the metadata > > > composed by the driver: > > > > Many production use case use XDP exactly for this. If it > > slows this basic use case down its going to be very hard > > to use in many environments. Likely it wont be used. > > > > > > > > meta off 21449 18078 16897 11820 6383 3610 > > > meta on 16956 19004 14337 8228 5683 2822 > > > GRO meta off 22539 19129 16304 11659 6381 3592 > > > GRO meta on 17047 20366 15435 8878 5600 2753 > > > > Do you have hardware that can write the data into the > > metadata region so you don't do it in software? Seems > > like it should be doable without much trouble and would > > make this more viable. > > > > > > > > Questions still open: > > > > > > * the actual generic structure: it must have all the fields used > > > oftenly and by the majority of NICs. It can always be expanded > > > later on (note that the structure grows to the left), but the > > > less often UAPI is modified, the better (less compat pain); > > > > I don't believe a generic structure is needed. > > > > > * ability to specify the exact fields to fill by the driver, e.g. > > > flags bitmap passed from the userspace. In theory it can be more > > > optimal to not spend cycles on data we don't need, but at the > > > same time increases the complexity of the whole concept (e.g. it > > > will be more problematic to unify drivers' routines for collecting > > > data from descriptors to metadata and to skbs); > > > * there was an idea to be able to specify from the userspace the > > > desired cacheline offset, so that [the wanted fields of] metadata > > > and the packet headers would lay in the same CL. Can't be > > > implemented in Generic/skb XDP and ice has some troubles with it > > > too; > > > * lacks AF_XDP/XSk perf numbers and different other scenarios in > > > general, is the current implementation optimal for them? > > > > AF_XDP is the primary use case from my understanding. > > > > AF_XDP is a use case, and might be the primary, but we work with pure XDP and > have been waiting for the ability to take advantage of the hardware checksums > for years. It would be a very large performance boost for us (in theory) as > we're currently having to verify the checksums ourselves in software, and > recompute them on modifications (since we can't use hardware TX checksums). Yes, there are plenty of people out there that want that boost both for XDP and AF_XDP, me included. So this work is important. > Also, if I understand correctly, if the functionality is available to pure XDP, > AF_XDP could benefit from it by having the XDP program that redirects to AF_XDP > copy it into metadata where AF_XDP can find it because of the user defined > contract between the XDP program and the userspace program? (Not as efficient, > obviously, and duplicative, but would work, I think.) Correct, AF_XDP can benefit from this directly. The metadata is already put before the packet, so in zero-copy mode it will be available to user-space at no extra cost. In copy mode though, it has to be copied out together with the packet data. But that code is already there since you can use the metadata section today for communicating information between XDP and user-space via AF_XDP. > > > * metadata threshold and everything else present in this > > > implementation. > > > > I really think your asking questions that are two or three > > jumps away. Why not do the simplest bit first and kick > > the driver with an on/off switch into this mode. But > > I don't understand this cpumap use case so maybe explain > > that first. > > > > And sorry didn't even look at your 50+ patches. Figure lets > > get agreement on the goal first. > > > > .John
From: John Fastabend <john.fastabend@gmail.com> Date: Tue, 28 Jun 2022 23:15:12 -0700 > Alexander Lobakin wrote: > > This RFC is to give the whole picture. It will most likely be split > > onto several series, maybe even merge cycles. See the "table of > > contents" below. > > Even for RFC its a bit much. Probably improve the summary > message here as well I'm still not clear on the overall > architecture so not sure I want to dig into patches. I wanted to give an overview to the whole code that I have for now. We have several series on 30+, even 60+ next to this one, I'm not sure I've seen a single "TL;DR" there. Same thing was with Matt's folio series, there was 165+, ok he didn't send it as is to LKML, but his words were "this is the first part, please take a look at the whole concept here[link]". I provided a "table of contents", so that anyone could go and review only stuff he's interested in, not touching the rest. My intention is that what if I submit the first part, then second, and then at the third someone says he doesn't like the idea and NACKs it, what then, if it all was supposed to work together as one? > > > > > The series adds ability to pass different frame > > details/parameters/parameters used by most of NICs and the kernel > > stack (in skbs), not essential, but highly wanted, such as: > > > > * checksum value, status (Rx) or command (Tx); > > * hash value and type/level (Rx); > > * queue number (Rx); > > * timestamps; > > * and so on. > > > > As XDP structures used to represent frames are as small as possible > > and must stay like that, it is done by using the already existing > > concept of metadata, i.e. some space right before a frame where BPF > > programs can put arbitrary data. > > OK so you stick attributes in the metadata. You can do this without > touching anything but your driver today. Why not push a patch to > ice to start doing this? People could start using it today and put > it in some feature flag. We have to configure it somehow, doesn't we? Do a feature flag for ice? Why doing anything "generic" then if I could just go with one driver and send it through our Intel mailing list? > > I get everyone wants some grand theory around this but again one > patch would do it and your customers could start using it. Show > a benchmark with 20% speedup or whatever with small XDP prog > update and you win. One patch would be a hardwiring/hardcoding everything on one button, what's the point if there were several such examples? This is RFC because the whole stuff needs to be discussed, not because a have some drafts and want to show them. It's finished and polished production-quality code which any vendor or customer could start using without rehardcoding for their own driver/needs/etc. I'm not following this "TL;DR" stuff, one can just apply the series and see how it goes/works for his needs (and then get back and report) even if he's not feeling like reviewing it. > > > > > Now, a NIC driver, or even a SmartNIC itself, can put those params > > there in a well-defined format. The format is fixed, but can be of > > several different types represented by structures, which definitions > > are available to the kernel, BPF programs and the userland. > > I don't think in general the format needs to be fixed. We discussed it previously as well, not only in regards to this stuff, but in general. For BPF programs, for sure we can CO-RE everything, but we also have: a) in-kernel users not hardcoded to a particular vendor/driver which just want to have generic fields in one format for every driver; b) AF_XDP/XSk programs which you can't CO-RE. There was a proposal from Alexei to patch LLVM to be able to apply CO-RE for AF_XDP (I mean, for ARM64/x86_64/etc. binaries) as well, but it's a whole different story with way more caveats. > > > It is fixed due to it being almost a UAPI, and the exact format can > > be determined by reading the last 10 bytes of metadata. They contain > > a 2-byte magic ID to not confuse it with a non-compatible meta and > > a 8-byte combined BTF ID + type ID: the ID of the BTF where this > > structure is defined and the ID of that definition inside that BTF. > > Users can obtain BTF IDs by structure types using helpers available > > in the kernel, BPF (written by the CO-RE/verifier) and the userland > > (libbpf -> kernel call) and then rely on those ID when reading data > > to make sure whether they support it and what to do with it. > > Why separate magic and ID? The idea is to make different formats > > always contain the basic/"generic" structure embedded at the end. > > This way we can still benefit in purely generic consumers (like > > cpumap) while providing some "extra" data to those who support it. > > I don't follow this. If you have a struct in your driver name it > something obvious, ice_xdp_metadata. If I understand things > correctly just dump the BTF for the driver, extract the > struct and done you can use CO-RE reads. For the 'fixed' case > this looks easy. And I don't think you even need a patch for this. > > > > > The enablement of this feature is controlled on attaching/replacing > > XDP program on an interface with two new parameters: that combined > > BTF+type ID and metadata threshold. > > The threshold specifies the minimum frame size which a driver (or > > NIC) should start composing metadata from. It is introduced instead > > of just false/true flag due to that often it's not worth it to spend > > cycles to fetch all that data for such small frames: let's say, it > > can be even faster to just calculate checksums for them on CPU > > rather than touch non-coherent DMA zone. Simple XDP_DROP case loses > > 15 Mpps on 64 byte frames with enabled metadata, threshold can help > > mitigate that. > > I would put this in the bonus category. Can you do the simple thing > above without these extra bits and then add them later. Just > pick some overly conservative threshold to start with. It's as simple as adding on/off button, there's no reason to leave it for later. Or is there? > > > > > The RFC can be divided into 8 parts: > > I'm missing something why not do the simplest bit of work and > get this running in ice with a few smallish driver updates > so we can all see it. No need for so many patches. Ok I should've write this down in the cover: it's not a draft or some hardcode to just show a PoC... > > > > > 01-04: BTF ID hacking: here Larysa provides BPF programs with not > > only type ID, but the ID of the BTF as well by using the > > unused upper 32 bits. > > 05-10: this provides in-kernel mechanisms for taking ID and > > threshold from the userspace and passing it to the drivers. > > 11-18: provides libbpf API to be able to specify those params from > > the userspace, plus some small selftest to verify that both > > the kernel and the userspace parts work. > > 19-29: here the actual structure is defined, then the in-kernel > > helpers and finally here comes the first consumer: function > > used to convert &xdp_frame to &sk_buff now will be trying > > to parse metadata. The affected users are cpumap and veth. > > 30-36: here I try to benefit from the metadata in cpumap even more > > by switching it to GRO. Now that we have checksums from NIC > > available... but even with no meta it gives some fair > > improvements. > > 37-43: enabling building generic metadata on Generic/skb path. Since > > skbs already have all those fields, it's not a problem to do > > this in here, plus allows to benefit from it on interfaces > > not supporting meta yet. > > 44-47: ice driver part, including enabling prog hot-swap; > > 48-52: adds a complex selftest to verify everything works. Can be > > used as a sample as well, showing how to work with metadata > > in BPF programs and how to configure it from the userspace. > > > > Please refer to the actual commit messages where some precise > > implementation details might be explained. > > Nearly 20 of 52 are various cleanups and prereqs, as usually. > > > > Perf figures were taken on cpumap redirect from the ice interface > > (driver-side XDP), redirecting the traffic within the same node. > > > > Frame size / 64/42 128/20 256/8 512/4 1024/2 1532/1 > > thread num > > You'll have to remind me whats the production use case for > cpu_map on a modern nic or even smart nic? Why are you not > just using a hardware queues and redirecting to the right > queues in hardware to start with? Load balancing, you can distribute packets not only by flows, but as you wish as you have full access to frames. Also, with RSS/RFS you serve interrupts and push a frame through the networking stack on the same CPU, with cpumap you can do the former on one and the latter on another one, and it's obviously faster. > > Also my understanding is if you do XDP_PASS up the stack > the skb is built with all the normal good stuff from hw > descriptor. Sorry going to need some extra context here > to understand. Correct, so this series makes cpumap on par (probably even better) with just %XDP_PASS. > > Could you do a benchmark for AF_XDP I thought this was > the troublesome use case where the user space ring lost > the hardware info e.g. timestamps and checksum values. Ok sure, a bit later. I wasn't focusing on AF_XDP, but it's there in the closest plans. > > > > > meta off 30022 31350 21993 12144 6374 3610 > > meta on 33059 28502 21503 12146 6380 3610 > > GRO meta off 30020 31822 21970 12145 6384 3610 > > GRO meta on 34736 28848 21566 12144 6381 3610 > > > > Yes, redirect between the nodes plays awfully with the metadata > > composed by the driver: > > Many production use case use XDP exactly for this. If it > slows this basic use case down its going to be very hard > to use in many environments. Likely it wont be used. Redirect between the nodes is not a good idea in general as you will be working with remote memory each redirect. Not sure it's widely used. And yes, SmartNICs don't have that problem if they're capable of composing arbitrary meta themselves. > > > > > meta off 21449 18078 16897 11820 6383 3610 > > meta on 16956 19004 14337 8228 5683 2822 > > GRO meta off 22539 19129 16304 11659 6381 3592 > > GRO meta on 17047 20366 15435 8878 5600 2753 > > Do you have hardware that can write the data into the > metadata region so you don't do it in software? Seems > like it should be doable without much trouble and would > make this more viable. For now I personally don't, but: a) some people do; b) I will in some time. IIRC, we were concering for both SmartNIC and "current generation" NICs not giving favour to any of them. > > > > > Questions still open: > > > > * the actual generic structure: it must have all the fields used > > oftenly and by the majority of NICs. It can always be expanded > > later on (note that the structure grows to the left), but the > > less often UAPI is modified, the better (less compat pain); > > I don't believe a generic structure is needed. Please see above. > > > * ability to specify the exact fields to fill by the driver, e.g. > > flags bitmap passed from the userspace. In theory it can be more > > optimal to not spend cycles on data we don't need, but at the > > same time increases the complexity of the whole concept (e.g. it > > will be more problematic to unify drivers' routines for collecting > > data from descriptors to metadata and to skbs); > > * there was an idea to be able to specify from the userspace the > > desired cacheline offset, so that [the wanted fields of] metadata > > and the packet headers would lay in the same CL. Can't be > > implemented in Generic/skb XDP and ice has some troubles with it > > too; > > * lacks AF_XDP/XSk perf numbers and different other scenarios in > > general, is the current implementation optimal for them? > > AF_XDP is the primary use case from my understanding. Not really, but is one of them. > > > * metadata threshold and everything else present in this > > implementation. > > I really think your asking questions that are two or three > jumps away. Why not do the simplest bit first and kick > the driver with an on/off switch into this mode. But > I don't understand this cpumap use case so maybe explain > that first. > > And sorry didn't even look at your 50+ patches. Figure lets > get agreement on the goal first. "TL;DR" will kill open source once ._. As I said, you could just pick whatever you want to look at, I never said "you, go and review cpumap GRO stuff" to anyone. > > .John Thanks, Olek
From: Toke Høiland-Jørgensen <toke@redhat.com> Date: Wed, 29 Jun 2022 15:43:05 +0200 > John Fastabend <john.fastabend@gmail.com> writes: > > > Alexander Lobakin wrote: > >> This RFC is to give the whole picture. It will most likely be split > >> onto several series, maybe even merge cycles. See the "table of > >> contents" below. > > > > Even for RFC its a bit much. Probably improve the summary > > message here as well I'm still not clear on the overall > > architecture so not sure I want to dig into patches. > > +1 on this, and piggybacking on your comment to chime in on the general > architecture. > > >> Now, a NIC driver, or even a SmartNIC itself, can put those params > >> there in a well-defined format. The format is fixed, but can be of > >> several different types represented by structures, which definitions > >> are available to the kernel, BPF programs and the userland. > > > > I don't think in general the format needs to be fixed. > > No, that's the whole point of BTF: it's not supposed to be UAPI, we'll > use CO-RE to enable dynamic formats... > > [...] > > >> It is fixed due to it being almost a UAPI, and the exact format can > >> be determined by reading the last 10 bytes of metadata. They contain > >> a 2-byte magic ID to not confuse it with a non-compatible meta and > >> a 8-byte combined BTF ID + type ID: the ID of the BTF where this > >> structure is defined and the ID of that definition inside that BTF. > >> Users can obtain BTF IDs by structure types using helpers available > >> in the kernel, BPF (written by the CO-RE/verifier) and the userland > >> (libbpf -> kernel call) and then rely on those ID when reading data > >> to make sure whether they support it and what to do with it. > >> Why separate magic and ID? The idea is to make different formats > >> always contain the basic/"generic" structure embedded at the end. > >> This way we can still benefit in purely generic consumers (like > >> cpumap) while providing some "extra" data to those who support it. > > > > I don't follow this. If you have a struct in your driver name it > > something obvious, ice_xdp_metadata. If I understand things > > correctly just dump the BTF for the driver, extract the > > struct and done you can use CO-RE reads. For the 'fixed' case > > this looks easy. And I don't think you even need a patch for this. > > ...however as we've discussed previously, we do need a bit of > infrastructure around this. In particular, we need to embed the embed > the BTF ID into the metadata itself so BPF can do runtime disambiguation > between different formats (and add the right CO-RE primitives to make > this easy). This is for two reasons: > > - The metadata might be different per-packet (e.g., PTP packets with > timestamps interleaved with bulk data without them) > > - With redirects we may end up processing packets from different devices > in a single XDP program (in devmap or cpumap, or on a veth) so we need > to be able to disambiguate at runtime. > > So I think the part of the design that puts the BTF ID into the end of > the metadata struct is sound; however, the actual format doesn't have to > be fixed, we can use CO-RE to pick out the bits that a given BPF program > needs; we just need a convention for how drivers report which format(s) > they support. Which we should also agree on (and add core infrastructure > around) so each driver doesn't go around inventing their own > conventions. > > >> The enablement of this feature is controlled on attaching/replacing > >> XDP program on an interface with two new parameters: that combined > >> BTF+type ID and metadata threshold. > >> The threshold specifies the minimum frame size which a driver (or > >> NIC) should start composing metadata from. It is introduced instead > >> of just false/true flag due to that often it's not worth it to spend > >> cycles to fetch all that data for such small frames: let's say, it > >> can be even faster to just calculate checksums for them on CPU > >> rather than touch non-coherent DMA zone. Simple XDP_DROP case loses > >> 15 Mpps on 64 byte frames with enabled metadata, threshold can help > >> mitigate that. > > > > I would put this in the bonus category. Can you do the simple thing > > above without these extra bits and then add them later. Just > > pick some overly conservative threshold to start with. > > Yeah, I'd agree this kind of configuration is something that can be > added later, and also it's sort of orthogonal to the consumption of the > metadata itself. > > Also, tying this configuration into the loading of an XDP program is a > terrible interface: these are hardware configuration options, let's just > put them into ethtool or 'ip link' like any other piece of device > configuration. I don't believe it fits there, especially Ethtool. Ethtool is for hardware configuration, XDP/AF_XDP is 95% software stuff (apart from offload bits which is purely NFP's for now). I follow that way: 1) you pick a program you want to attach; 2) usually they are written for special needs and usecases; 3) so most likely that program will be tied with metadata/driver/etc in some way; 4) so you want to enable Hints of a particular format primarily for this program and usecase, same with threshold and everything else. Pls explain how you see it, I might be wrong for sure. > > >> The RFC can be divided into 8 parts: > > > > I'm missing something why not do the simplest bit of work and > > get this running in ice with a few smallish driver updates > > so we can all see it. No need for so many patches. > > Agreed. This incremental approach is basically what Jesper's > simultaneous series makes a start on, AFAICT? Would be nice if y'all > could converge the efforts :) I don't know why at some point Jesper decided to go on his own as he for sure was using our tree as a base for some time, dunno what happened then. Regarding these two particular submissions, I didn't see Jesper's RFC when sending mine, only after when I went to read some stuff. > > [...] > > > I really think your asking questions that are two or three > > jumps away. Why not do the simplest bit first and kick > > the driver with an on/off switch into this mode. But > > I don't understand this cpumap use case so maybe explain > > that first. > > > > And sorry didn't even look at your 50+ patches. Figure lets > > get agreement on the goal first. > > +1 on both of these :) I just thought most of parts were already discussed previously and the reason I marked it "RFC" was that there are lots of changes and not everyone may agree with them... Like "here's overview of what was discussed and what we decided previously, let's review it to see if there are any questionable/debatable stuff and agree on those 3 questions, then I'll split it according to my taste or to how the maintainers see it and apply it slow'n'steady". > > -Toke Thanks, Olek
On 04/07/2022 17.44, Alexander Lobakin wrote: >> Agreed. This incremental approach is basically what Jesper's >> simultaneous series makes a start on, AFAICT? Would be nice if y'all >> could converge the efforts :) > > I don't know why at some point Jesper decided to go on his own as he > for sure was using our tree as a base for some time, dunno what > happened then. Regarding these two particular submissions, I didn't > see Jesper's RFC when sending mine, only after when I went to read > some stuff. > Well, I have written to you (offlist) that the git tree didn't compile, so I had a hard time getting it into a working state. We had a ping-pong of stuff to fix, but it wasn't and you basically told me to switch to using LLVM to compile your kernel tree, I was not interested in doing that. I have looked at the code in your GitHub tree, and decided that it was an over-engineered approach IMHO. Also simply being 52 commits deep without having posted this incrementally upstream were also a non-starter for me, as this isn't the way-to-work upstream. To get the ball rolling, I have implemented the base XDP-hints support here[1] with only 9 patches (including support for two drivers). IMHO we need to start out small and not intermix these huge refactoring patches. E.g. I'm not convinced renaming net/{core/xdp.c => bpf/core.c} is an improvement. -Jesper [1] https://lore.kernel.org/bpf/165643378969.449467.13237011812569188299.stgit@firesoul/
Alexander Lobakin <alexandr.lobakin@intel.com> writes: > From: Toke H??iland-J??rgensen <toke@redhat.com> > Date: Wed, 29 Jun 2022 15:43:05 +0200 > >> John Fastabend <john.fastabend@gmail.com> writes: >> >> > Alexander Lobakin wrote: >> >> This RFC is to give the whole picture. It will most likely be split >> >> onto several series, maybe even merge cycles. See the "table of >> >> contents" below. >> > >> > Even for RFC its a bit much. Probably improve the summary >> > message here as well I'm still not clear on the overall >> > architecture so not sure I want to dig into patches. >> >> +1 on this, and piggybacking on your comment to chime in on the general >> architecture. >> >> >> Now, a NIC driver, or even a SmartNIC itself, can put those params >> >> there in a well-defined format. The format is fixed, but can be of >> >> several different types represented by structures, which definitions >> >> are available to the kernel, BPF programs and the userland. >> > >> > I don't think in general the format needs to be fixed. >> >> No, that's the whole point of BTF: it's not supposed to be UAPI, we'll >> use CO-RE to enable dynamic formats... >> >> [...] >> >> >> It is fixed due to it being almost a UAPI, and the exact format can >> >> be determined by reading the last 10 bytes of metadata. They contain >> >> a 2-byte magic ID to not confuse it with a non-compatible meta and >> >> a 8-byte combined BTF ID + type ID: the ID of the BTF where this >> >> structure is defined and the ID of that definition inside that BTF. >> >> Users can obtain BTF IDs by structure types using helpers available >> >> in the kernel, BPF (written by the CO-RE/verifier) and the userland >> >> (libbpf -> kernel call) and then rely on those ID when reading data >> >> to make sure whether they support it and what to do with it. >> >> Why separate magic and ID? The idea is to make different formats >> >> always contain the basic/"generic" structure embedded at the end. >> >> This way we can still benefit in purely generic consumers (like >> >> cpumap) while providing some "extra" data to those who support it. >> > >> > I don't follow this. If you have a struct in your driver name it >> > something obvious, ice_xdp_metadata. If I understand things >> > correctly just dump the BTF for the driver, extract the >> > struct and done you can use CO-RE reads. For the 'fixed' case >> > this looks easy. And I don't think you even need a patch for this. >> >> ...however as we've discussed previously, we do need a bit of >> infrastructure around this. In particular, we need to embed the embed >> the BTF ID into the metadata itself so BPF can do runtime disambiguation >> between different formats (and add the right CO-RE primitives to make >> this easy). This is for two reasons: >> >> - The metadata might be different per-packet (e.g., PTP packets with >> timestamps interleaved with bulk data without them) >> >> - With redirects we may end up processing packets from different devices >> in a single XDP program (in devmap or cpumap, or on a veth) so we need >> to be able to disambiguate at runtime. >> >> So I think the part of the design that puts the BTF ID into the end of >> the metadata struct is sound; however, the actual format doesn't have to >> be fixed, we can use CO-RE to pick out the bits that a given BPF program >> needs; we just need a convention for how drivers report which format(s) >> they support. Which we should also agree on (and add core infrastructure >> around) so each driver doesn't go around inventing their own >> conventions. >> >> >> The enablement of this feature is controlled on attaching/replacing >> >> XDP program on an interface with two new parameters: that combined >> >> BTF+type ID and metadata threshold. >> >> The threshold specifies the minimum frame size which a driver (or >> >> NIC) should start composing metadata from. It is introduced instead >> >> of just false/true flag due to that often it's not worth it to spend >> >> cycles to fetch all that data for such small frames: let's say, it >> >> can be even faster to just calculate checksums for them on CPU >> >> rather than touch non-coherent DMA zone. Simple XDP_DROP case loses >> >> 15 Mpps on 64 byte frames with enabled metadata, threshold can help >> >> mitigate that. >> > >> > I would put this in the bonus category. Can you do the simple thing >> > above without these extra bits and then add them later. Just >> > pick some overly conservative threshold to start with. >> >> Yeah, I'd agree this kind of configuration is something that can be >> added later, and also it's sort of orthogonal to the consumption of the >> metadata itself. >> >> Also, tying this configuration into the loading of an XDP program is a >> terrible interface: these are hardware configuration options, let's just >> put them into ethtool or 'ip link' like any other piece of device >> configuration. > > I don't believe it fits there, especially Ethtool. Ethtool is for > hardware configuration, XDP/AF_XDP is 95% software stuff (apart from > offload bits which is purely NFP's for now). But XDP-hints is about consuming hardware features. When you're configuring which metadata items you want, you're saying "please provide me with these (hardware) features". So ethtool is an excellent place to do that :) > I follow that way: > > 1) you pick a program you want to attach; > 2) usually they are written for special needs and usecases; > 3) so most likely that program will be tied with metadata/driver/etc > in some way; > 4) so you want to enable Hints of a particular format primarily for > this program and usecase, same with threshold and everything > else. > > Pls explain how you see it, I might be wrong for sure. As above: XDP hints is about giving XDP programs (and AF_XDP consumers) access to metadata that is not currently available. Tying the lifetime of that hardware configuration (i.e., which information to provide) to the lifetime of an XDP program is not a good interface: for one thing, how will it handle multiple programs? What about when XDP is not used at all but you still want to configure the same features? In addition, in every other case where we do dynamic data access (with CO-RE) the BPF program is a consumer that modifies itself to access the data provided by the kernel. I get that this is harder to achieve for AF_XDP, but then let's solve that instead of making a totally inconsistent interface for XDP. I'm as excited as you about the prospect of having totally programmable hardware where you can just specify any arbitrary metadata format and it'll provide that for you. But that is an orthogonal feature: let's start with creating a dynamic interface for consuming the (static) hardware features we already have, and then later we can have a separate interface for configuring more dynamic hardware features. XDP-hints is about adding this consumption feature in a way that's sufficiently dynamic that we can do the other (programmable hardware) thing on top later... -Toke
From: Jesper Dangaard Brouer <jbrouer@redhat.com> Date: Mon, 4 Jul 2022 19:13:53 +0200 > On 04/07/2022 17.44, Alexander Lobakin wrote: > >> Agreed. This incremental approach is basically what Jesper's > >> simultaneous series makes a start on, AFAICT? Would be nice if y'all > >> could converge the efforts :) > > > I don't know why at some point Jesper decided to go on his own as he > > for sure was using our tree as a base for some time, dunno what > > happened then. Regarding these two particular submissions, I didn't > > see Jesper's RFC when sending mine, only after when I went to read > > some stuff. > > > > Well, I have written to you (offlist) that the git tree didn't compile, > so I had a hard time getting it into a working state. We had a > ping-pong of stuff to fix, but it wasn't and you basically told me to > switch to using LLVM to compile your kernel tree, I was not interested > in doing that. Yes and no, I only told you that I missed those build issues due to that I use LLVM as my primary compiler, but I didn't suggest you switch to it. Then I fixed all of the issues in a couple days and wrote you the email on 3th of June saying that everything works now =\ > > I have looked at the code in your GitHub tree, and decided that it was > an over-engineered approach IMHO. Also simply being 52 commits deep > without having posted this incrementally upstream were also a > non-starter for me, as this isn't the way-to-work upstream. So Ingo announced recently that he has a series of 2300+ patches to try to fix include hell. Now he's preparing to submit them by batches/series. Look at this RFC as at an announce. "Hey folks, I have a bunch of stuff and will be submitting it soon, but I'm posting the whole changeset here, so you could take a look or give it a try before it's actually started being posted". All this is mentioned in the cover letter as well. What is the problem? Ok, next time I can not do any announces and just start posting series if it made such misunderstandings. Anyway, I will post a demo-version of the series in a couple weeks containing only the parts required to get Hints working on ice if folks prefer to look at the pencil draft instead of looking at the final painting (never thought I'll have to do that in the kernel dev community :D). > > To get the ball rolling, I have implemented the base XDP-hints support > here[1] with only 9 patches (including support for two drivers). > > IMHO we need to start out small and not intermix these huge refactoring > patches. E.g. I'm not convinced renaming net/{core/xdp.c => bpf/core.c} > is an improvement. Those cleanup patches can be easily put in a standalone series as a prerequisite. I even mentioned them in the cover letter. File names is a matter of discussing, my intention there was mainly to move XDP stuff out of overburdened net/core/dev.c. > > -Jesper > > [1] > https://lore.kernel.org/bpf/165643378969.449467.13237011812569188299.stgit@firesoul/ Thanks, Olek
From: Toke Høiland-Jørgensen <toke@redhat.com> Date: Mon, 04 Jul 2022 19:14:04 +0200 > Alexander Lobakin <alexandr.lobakin@intel.com> writes: > > > From: Toke H??iland-J??rgensen <toke@redhat.com> > > Date: Wed, 29 Jun 2022 15:43:05 +0200 > > > >> John Fastabend <john.fastabend@gmail.com> writes: > >> > >> > Alexander Lobakin wrote: > >> >> This RFC is to give the whole picture. It will most likely be split > >> >> onto several series, maybe even merge cycles. See the "table of > >> >> contents" below. > >> > > >> > Even for RFC its a bit much. Probably improve the summary > >> > message here as well I'm still not clear on the overall > >> > architecture so not sure I want to dig into patches. > >> > >> +1 on this, and piggybacking on your comment to chime in on the general > >> architecture. > >> > >> >> Now, a NIC driver, or even a SmartNIC itself, can put those params > >> >> there in a well-defined format. The format is fixed, but can be of > >> >> several different types represented by structures, which definitions > >> >> are available to the kernel, BPF programs and the userland. > >> > > >> > I don't think in general the format needs to be fixed. > >> > >> No, that's the whole point of BTF: it's not supposed to be UAPI, we'll > >> use CO-RE to enable dynamic formats... > >> > >> [...] > >> > >> >> It is fixed due to it being almost a UAPI, and the exact format can > >> >> be determined by reading the last 10 bytes of metadata. They contain > >> >> a 2-byte magic ID to not confuse it with a non-compatible meta and > >> >> a 8-byte combined BTF ID + type ID: the ID of the BTF where this > >> >> structure is defined and the ID of that definition inside that BTF. > >> >> Users can obtain BTF IDs by structure types using helpers available > >> >> in the kernel, BPF (written by the CO-RE/verifier) and the userland > >> >> (libbpf -> kernel call) and then rely on those ID when reading data > >> >> to make sure whether they support it and what to do with it. > >> >> Why separate magic and ID? The idea is to make different formats > >> >> always contain the basic/"generic" structure embedded at the end. > >> >> This way we can still benefit in purely generic consumers (like > >> >> cpumap) while providing some "extra" data to those who support it. > >> > > >> > I don't follow this. If you have a struct in your driver name it > >> > something obvious, ice_xdp_metadata. If I understand things > >> > correctly just dump the BTF for the driver, extract the > >> > struct and done you can use CO-RE reads. For the 'fixed' case > >> > this looks easy. And I don't think you even need a patch for this. > >> > >> ...however as we've discussed previously, we do need a bit of > >> infrastructure around this. In particular, we need to embed the embed > >> the BTF ID into the metadata itself so BPF can do runtime disambiguation > >> between different formats (and add the right CO-RE primitives to make > >> this easy). This is for two reasons: > >> > >> - The metadata might be different per-packet (e.g., PTP packets with > >> timestamps interleaved with bulk data without them) > >> > >> - With redirects we may end up processing packets from different devices > >> in a single XDP program (in devmap or cpumap, or on a veth) so we need > >> to be able to disambiguate at runtime. > >> > >> So I think the part of the design that puts the BTF ID into the end of > >> the metadata struct is sound; however, the actual format doesn't have to > >> be fixed, we can use CO-RE to pick out the bits that a given BPF program > >> needs; we just need a convention for how drivers report which format(s) > >> they support. Which we should also agree on (and add core infrastructure > >> around) so each driver doesn't go around inventing their own > >> conventions. > >> > >> >> The enablement of this feature is controlled on attaching/replacing > >> >> XDP program on an interface with two new parameters: that combined > >> >> BTF+type ID and metadata threshold. > >> >> The threshold specifies the minimum frame size which a driver (or > >> >> NIC) should start composing metadata from. It is introduced instead > >> >> of just false/true flag due to that often it's not worth it to spend > >> >> cycles to fetch all that data for such small frames: let's say, it > >> >> can be even faster to just calculate checksums for them on CPU > >> >> rather than touch non-coherent DMA zone. Simple XDP_DROP case loses > >> >> 15 Mpps on 64 byte frames with enabled metadata, threshold can help > >> >> mitigate that. > >> > > >> > I would put this in the bonus category. Can you do the simple thing > >> > above without these extra bits and then add them later. Just > >> > pick some overly conservative threshold to start with. > >> > >> Yeah, I'd agree this kind of configuration is something that can be > >> added later, and also it's sort of orthogonal to the consumption of the > >> metadata itself. > >> > >> Also, tying this configuration into the loading of an XDP program is a > >> terrible interface: these are hardware configuration options, let's just > >> put them into ethtool or 'ip link' like any other piece of device > >> configuration. > > > > I don't believe it fits there, especially Ethtool. Ethtool is for > > hardware configuration, XDP/AF_XDP is 95% software stuff (apart from > > offload bits which is purely NFP's for now). > > But XDP-hints is about consuming hardware features. When you're > configuring which metadata items you want, you're saying "please provide > me with these (hardware) features". So ethtool is an excellent place to > do that :) With Ethtool you configure the hardware, e.g. it won't strip VLAN tags if you disable rx-cvlan-stripping. With configuring metadata you only tell what you want to see there, don't you? > > > I follow that way: > > > > 1) you pick a program you want to attach; > > 2) usually they are written for special needs and usecases; > > 3) so most likely that program will be tied with metadata/driver/etc > > in some way; > > 4) so you want to enable Hints of a particular format primarily for > > this program and usecase, same with threshold and everything > > else. > > > > Pls explain how you see it, I might be wrong for sure. > > As above: XDP hints is about giving XDP programs (and AF_XDP consumers) > access to metadata that is not currently available. Tying the lifetime > of that hardware configuration (i.e., which information to provide) to > the lifetime of an XDP program is not a good interface: for one thing, > how will it handle multiple programs? What about when XDP is not used at Multiple progs is stuff I didn't cover, but will do later (as you all say to me, "let's start with something simple" :)). Aaaand multiple XDP progs (I'm not talking about attaching progs in differeng modes) is not a kernel feature, rather a libpf feature, so I believe it should be handled there later... > all but you still want to configure the same features? What's the point of configuring metadata when there are no progs attached? To configure it once and not on every prog attach? I'm not saying I don't like it, just want to clarify. Maybe I need opinions from some more people, just to have an overview of how most of folks see it and would like to configure it. 'Cause I heard from at least one of the consumers that libpf API is a perfect place for Hints to him :) > > In addition, in every other case where we do dynamic data access (with > CO-RE) the BPF program is a consumer that modifies itself to access the > data provided by the kernel. I get that this is harder to achieve for > AF_XDP, but then let's solve that instead of making a totally > inconsistent interface for XDP. I also see CO-RE more fitting and convenient way to use them, but didn't manage to solve two things: 1) AF_XDP programs, so what to do with them? Prepare patches for LLVM to make it able to do CO-RE on AF_XDP program load? Or just hardcode them for particular usecases and NICs? What about "general-purpose" programs? And if hardcode, what's the point then to do Generic Hints at all? Then all it needs is making driver building some meta in front of frames via on-off button and that's it? Why BTF ID in the meta then if consumers will access meta hardcoded (via CO-RE or literally hardcoded, doesn't matter)? 2) In-kernel metadata consumers? Also do CO-RE? Otherwise, with no generic metadata structure they won't be able to benefit from Hints. But I guess we still need to provide kernel with meta? Or no? > > I'm as excited as you about the prospect of having totally programmable But I mostly care about current generation with no programmable Hints... > hardware where you can just specify any arbitrary metadata format and > it'll provide that for you. But that is an orthogonal feature: let's > start with creating a dynamic interface for consuming the (static) > hardware features we already have, and then later we can have a separate > interface for configuring more dynamic hardware features. XDP-hints is > about adding this consumption feature in a way that's sufficiently > dynamic that we can do the other (programmable hardware) thing on top > later... > > -Toke Thanks, Olek
Alexander Lobakin <alexandr.lobakin@intel.com> writes: [... snipping a bit of context here ...] >> >> Yeah, I'd agree this kind of configuration is something that can be >> >> added later, and also it's sort of orthogonal to the consumption of the >> >> metadata itself. >> >> >> >> Also, tying this configuration into the loading of an XDP program is a >> >> terrible interface: these are hardware configuration options, let's just >> >> put them into ethtool or 'ip link' like any other piece of device >> >> configuration. >> > >> > I don't believe it fits there, especially Ethtool. Ethtool is for >> > hardware configuration, XDP/AF_XDP is 95% software stuff (apart from >> > offload bits which is purely NFP's for now). >> >> But XDP-hints is about consuming hardware features. When you're >> configuring which metadata items you want, you're saying "please provide >> me with these (hardware) features". So ethtool is an excellent place to >> do that :) > > With Ethtool you configure the hardware, e.g. it won't strip VLAN > tags if you disable rx-cvlan-stripping. With configuring metadata > you only tell what you want to see there, don't you? Ah, I think we may be getting closer to identifying the disconnect between our way of thinking about this! In my mind, there's no separate "configuration of the metadata" step. You simply tell the hardware what features you want (say, "enable timestamps and VLAN offload"), and the driver will then provide the information related to these features in the metadata area unconditionally. All XDP hints is about, then, is a way for the driver to inform the rest of the system how that information is actually laid out in the metadata area. Having a separate configuration knob to tell the driver "please lay out these particular bits of metadata this way" seems like a totally unnecessary (and quite complicated) feature to have when we can just let the driver decide and use CO-RE to consume it? >> > I follow that way: >> > >> > 1) you pick a program you want to attach; >> > 2) usually they are written for special needs and usecases; >> > 3) so most likely that program will be tied with metadata/driver/etc >> > in some way; >> > 4) so you want to enable Hints of a particular format primarily for >> > this program and usecase, same with threshold and everything >> > else. >> > >> > Pls explain how you see it, I might be wrong for sure. >> >> As above: XDP hints is about giving XDP programs (and AF_XDP consumers) >> access to metadata that is not currently available. Tying the lifetime >> of that hardware configuration (i.e., which information to provide) to >> the lifetime of an XDP program is not a good interface: for one thing, >> how will it handle multiple programs? What about when XDP is not used at > > Multiple progs is stuff I didn't cover, but will do later (as you > all say to me, "let's start with something simple" :)). Aaaand > multiple XDP progs (I'm not talking about attaching progs in > differeng modes) is not a kernel feature, rather a libpf feature, > so I believe it should be handled there later... Right, but even if we don't *implement* it straight away we still need to take it into consideration in the design. And expecting libxdp to arbitrate between different XDP programs' metadata formats sounds like a royal PITA :) >> all but you still want to configure the same features? > > What's the point of configuring metadata when there are no progs > attached? To configure it once and not on every prog attach? I'm > not saying I don't like it, just want to clarify. See above: you turn on the features because you want the stack to consume them. > Maybe I need opinions from some more people, just to have an > overview of how most of folks see it and would like to configure > it. 'Cause I heard from at least one of the consumers that > libpf API is a perfect place for Hints to him :) Well, as a program author who wants to consume hints, you'd use lib{bpf,xdp} APIs to do so (probably in the form of suitable CO-RE macros)... >> In addition, in every other case where we do dynamic data access (with >> CO-RE) the BPF program is a consumer that modifies itself to access the >> data provided by the kernel. I get that this is harder to achieve for >> AF_XDP, but then let's solve that instead of making a totally >> inconsistent interface for XDP. > > I also see CO-RE more fitting and convenient way to use them, but > didn't manage to solve two things: > > 1) AF_XDP programs, so what to do with them? Prepare patches for > LLVM to make it able to do CO-RE on AF_XDP program load? Or > just hardcode them for particular usecases and NICs? What about > "general-purpose" programs? You provide a library to read the fields. Jesper actually already implemented this, did you look at his code? https://github.com/xdp-project/bpf-examples/tree/master/AF_XDP-interaction It basically builds a lookup table at load-time using BTF information from the kernel, keyed on BTF ID and field name, resolving them into offsets. It's not quite the zero-overhead of CO-RE, but it's fairly close and can be improved upon (CO-RE for userspace being one way of doing that). > And if hardcode, what's the point then to do Generic Hints at > all? Then all it needs is making driver building some meta in > front of frames via on-off button and that's it? Why BTF ID in > the meta then if consumers will access meta hardcoded (via CO-RE > or literally hardcoded, doesn't matter)? You're quite right, we could probably implement all the access to existing (fixed) metadata without using any BTF at all - just define a common struct and some flags to designate which fields are set. In my mind, there are a couple of reasons for going the BTF route instead: - We can leverage CO-RE to get close to optimal efficiency in field access. and, more importantly: - It's infinitely extensible. With the infrastructure in place to make it really easy to consume metadata described by BTF, we lower the bar for future innovation in hardware offloads. Both for just adding new fixed-function stuff to hardware, but especially for fully programmable hardware. > 2) In-kernel metadata consumers? Also do CO-RE? Otherwise, with no > generic metadata structure they won't be able to benefit from > Hints. But I guess we still need to provide kernel with meta? > Or no? In the short term, I think the "generic structure" approach is fine for leveraging this in the stack. Both your and Jesper's series include this, and I think that's totally fine. Longer term, if it turns out to be useful to have something more dynamic for the stack consumption as well, we could extend it to be CO-RE based as well (most likely by having the stack load a "translator" BPF program or something along those lines). >> I'm as excited as you about the prospect of having totally programmable > > But I mostly care about current generation with no programmable > Hints... Well, see above; we should be able to support both :) -Toke
On 7/5/22 4:38 PM, Alexander Lobakin wrote: > From: Jesper Dangaard Brouer <jbrouer@redhat.com> > Date: Mon, 4 Jul 2022 19:13:53 +0200 [...] >> I have looked at the code in your GitHub tree, and decided that it was >> an over-engineered approach IMHO. Also simply being 52 commits deep >> without having posted this incrementally upstream were also a >> non-starter for me, as this isn't the way-to-work upstream. > > So Ingo announced recently that he has a series of 2300+ patches > to try to fix include hell. Now he's preparing to submit them by > batches/series. Look at this RFC as at an announce. "Hey folks, > I have a bunch of stuff and will be submitting it soon, but I'm > posting the whole changeset here, so you could take a look or > give it a try before it's actually started being posted". > All this is mentioned in the cover letter as well. What is the > problem? Ok, next time I can not do any announces and just start > posting series if it made such misunderstandings. I would suggest to please calm down first. No offense, but above example with the 2300+ patches is not a great one. There is no way any mortal would be able to review them, not even thinking about the cycles spent around rebasing, merge conflict resolution or bugs they may contain. Anyway, that aside.. Your series essentially starts out with ... The series adds ability to pass different frame details/parameters/parameters used by most of NICs and the kernel stack (in skbs), not essential, but highly wanted, such as: * checksum value, status (Rx) or command (Tx); * hash value and type/level (Rx); * queue number (Rx); * timestamps; * and so on. ... so my initial question would be whether in this context there has been done research / analysis of how this can speed up /real world/ production applications such as Katran L4LB [0], for example? What is the speedup you observed with it by utilizing the fields from meta data? Thanks, Daniel [0] https://github.com/facebookincubator/katran
From: Toke Høiland-Jørgensen <toke@redhat.com> Date: Tue, 05 Jul 2022 20:51:14 +0200 > Alexander Lobakin <alexandr.lobakin@intel.com> writes: > > [... snipping a bit of context here ...] > > >> >> Yeah, I'd agree this kind of configuration is something that can be > >> >> added later, and also it's sort of orthogonal to the consumption of the > >> >> metadata itself. > >> >> > >> >> Also, tying this configuration into the loading of an XDP program is a > >> >> terrible interface: these are hardware configuration options, let's just > >> >> put them into ethtool or 'ip link' like any other piece of device > >> >> configuration. > >> > > >> > I don't believe it fits there, especially Ethtool. Ethtool is for > >> > hardware configuration, XDP/AF_XDP is 95% software stuff (apart from > >> > offload bits which is purely NFP's for now). > >> > >> But XDP-hints is about consuming hardware features. When you're > >> configuring which metadata items you want, you're saying "please provide > >> me with these (hardware) features". So ethtool is an excellent place to > >> do that :) > > > > With Ethtool you configure the hardware, e.g. it won't strip VLAN > > tags if you disable rx-cvlan-stripping. With configuring metadata > > you only tell what you want to see there, don't you? > > Ah, I think we may be getting closer to identifying the disconnect > between our way of thinking about this! > > In my mind, there's no separate "configuration of the metadata" step. > You simply tell the hardware what features you want (say, "enable > timestamps and VLAN offload"), and the driver will then provide the > information related to these features in the metadata area > unconditionally. All XDP hints is about, then, is a way for the driver > to inform the rest of the system how that information is actually laid > out in the metadata area. > > Having a separate configuration knob to tell the driver "please lay out > these particular bits of metadata this way" seems like a totally > unnecessary (and quite complicated) feature to have when we can just let > the driver decide and use CO-RE to consume it? Magnus (he's currently on vacation) told me it would be useful for AF_XDP to enable/disable particular metadata, at least from perf perspective. Let's say, just fetching of one "checksum ok" bit in the driver is faster than walking through all the descriptor words and driver logics (i.e. there's several hundred locs in ice which just parse descriptor data and build an skb or metadata from it). But if we would just enable/disable corresponding features through Ethtool, that would hurt XDP_PASS. Maybe it's a bad example, but what if I want to have only RSS hash in the metadata (and don't want to spend cycles on parsing the rest), but at the same time still want skb path to have checksum status to not die at CPU checksum calculation? > > >> > I follow that way: > >> > > >> > 1) you pick a program you want to attach; > >> > 2) usually they are written for special needs and usecases; > >> > 3) so most likely that program will be tied with metadata/driver/etc > >> > in some way; > >> > 4) so you want to enable Hints of a particular format primarily for > >> > this program and usecase, same with threshold and everything > >> > else. > >> > > >> > Pls explain how you see it, I might be wrong for sure. > >> > >> As above: XDP hints is about giving XDP programs (and AF_XDP consumers) > >> access to metadata that is not currently available. Tying the lifetime > >> of that hardware configuration (i.e., which information to provide) to > >> the lifetime of an XDP program is not a good interface: for one thing, > >> how will it handle multiple programs? What about when XDP is not used at > > > > Multiple progs is stuff I didn't cover, but will do later (as you > > all say to me, "let's start with something simple" :)). Aaaand > > multiple XDP progs (I'm not talking about attaching progs in > > differeng modes) is not a kernel feature, rather a libpf feature, > > so I believe it should be handled there later... > > Right, but even if we don't *implement* it straight away we still need > to take it into consideration in the design. And expecting libxdp to > arbitrate between different XDP programs' metadata formats sounds like a > royal PITA :) > > >> all but you still want to configure the same features? > > > > What's the point of configuring metadata when there are no progs > > attached? To configure it once and not on every prog attach? I'm > > not saying I don't like it, just want to clarify. > > See above: you turn on the features because you want the stack to > consume them. > > > Maybe I need opinions from some more people, just to have an > > overview of how most of folks see it and would like to configure > > it. 'Cause I heard from at least one of the consumers that > > libpf API is a perfect place for Hints to him :) > > Well, as a program author who wants to consume hints, you'd use > lib{bpf,xdp} APIs to do so (probably in the form of suitable CO-RE > macros)... > > >> In addition, in every other case where we do dynamic data access (with > >> CO-RE) the BPF program is a consumer that modifies itself to access the > >> data provided by the kernel. I get that this is harder to achieve for > >> AF_XDP, but then let's solve that instead of making a totally > >> inconsistent interface for XDP. > > > > I also see CO-RE more fitting and convenient way to use them, but > > didn't manage to solve two things: > > > > 1) AF_XDP programs, so what to do with them? Prepare patches for > > LLVM to make it able to do CO-RE on AF_XDP program load? Or > > just hardcode them for particular usecases and NICs? What about > > "general-purpose" programs? > > You provide a library to read the fields. Jesper actually already > implemented this, did you look at his code? > > https://github.com/xdp-project/bpf-examples/tree/master/AF_XDP-interaction > > It basically builds a lookup table at load-time using BTF information > from the kernel, keyed on BTF ID and field name, resolving them into > offsets. It's not quite the zero-overhead of CO-RE, but it's fairly > close and can be improved upon (CO-RE for userspace being one way of > doing that). Aaaah, sorry, I completely missed that. I thought of something similar as well, but then thought "variable field offsets, that would annihilate optimization and performance", and our Xsk team is super concerned about performance hits when using Hints. > > > And if hardcode, what's the point then to do Generic Hints at > > all? Then all it needs is making driver building some meta in > > front of frames via on-off button and that's it? Why BTF ID in > > the meta then if consumers will access meta hardcoded (via CO-RE > > or literally hardcoded, doesn't matter)? > > You're quite right, we could probably implement all the access to > existing (fixed) metadata without using any BTF at all - just define a > common struct and some flags to designate which fields are set. In my > mind, there are a couple of reasons for going the BTF route instead: > > - We can leverage CO-RE to get close to optimal efficiency in field > access. > > and, more importantly: > > - It's infinitely extensible. With the infrastructure in place to make > it really easy to consume metadata described by BTF, we lower the bar > for future innovation in hardware offloads. Both for just adding new > fixed-function stuff to hardware, but especially for fully > programmable hardware. Agree :) That libxdp lookup translator fixed lots of stuff in my mind. > > > 2) In-kernel metadata consumers? Also do CO-RE? Otherwise, with no > > generic metadata structure they won't be able to benefit from > > Hints. But I guess we still need to provide kernel with meta? > > Or no? > > In the short term, I think the "generic structure" approach is fine for > leveraging this in the stack. Both your and Jesper's series include > this, and I think that's totally fine. Longer term, if it turns out to > be useful to have something more dynamic for the stack consumption as > well, we could extend it to be CO-RE based as well (most likely by > having the stack load a "translator" BPF program or something along > those lines). Oh, that translator prog sounds nice BTW! > > >> I'm as excited as you about the prospect of having totally programmable > > > > But I mostly care about current generation with no programmable > > Hints... > > Well, see above; we should be able to support both :) > > -Toke Thanks, Olek
Alexander Lobakin <alexandr.lobakin@intel.com> writes: > From: Toke H??iland-J??rgensen <toke@redhat.com> > Date: Tue, 05 Jul 2022 20:51:14 +0200 > >> Alexander Lobakin <alexandr.lobakin@intel.com> writes: >> >> [... snipping a bit of context here ...] >> >> >> >> Yeah, I'd agree this kind of configuration is something that can be >> >> >> added later, and also it's sort of orthogonal to the consumption of the >> >> >> metadata itself. >> >> >> >> >> >> Also, tying this configuration into the loading of an XDP program is a >> >> >> terrible interface: these are hardware configuration options, let's just >> >> >> put them into ethtool or 'ip link' like any other piece of device >> >> >> configuration. >> >> > >> >> > I don't believe it fits there, especially Ethtool. Ethtool is for >> >> > hardware configuration, XDP/AF_XDP is 95% software stuff (apart from >> >> > offload bits which is purely NFP's for now). >> >> >> >> But XDP-hints is about consuming hardware features. When you're >> >> configuring which metadata items you want, you're saying "please provide >> >> me with these (hardware) features". So ethtool is an excellent place to >> >> do that :) >> > >> > With Ethtool you configure the hardware, e.g. it won't strip VLAN >> > tags if you disable rx-cvlan-stripping. With configuring metadata >> > you only tell what you want to see there, don't you? >> >> Ah, I think we may be getting closer to identifying the disconnect >> between our way of thinking about this! >> >> In my mind, there's no separate "configuration of the metadata" step. >> You simply tell the hardware what features you want (say, "enable >> timestamps and VLAN offload"), and the driver will then provide the >> information related to these features in the metadata area >> unconditionally. All XDP hints is about, then, is a way for the driver >> to inform the rest of the system how that information is actually laid >> out in the metadata area. >> >> Having a separate configuration knob to tell the driver "please lay out >> these particular bits of metadata this way" seems like a totally >> unnecessary (and quite complicated) feature to have when we can just let >> the driver decide and use CO-RE to consume it? > > Magnus (he's currently on vacation) told me it would be useful for > AF_XDP to enable/disable particular metadata, at least from perf > perspective. Let's say, just fetching of one "checksum ok" bit in > the driver is faster than walking through all the descriptor words > and driver logics (i.e. there's several hundred locs in ice which > just parse descriptor data and build an skb or metadata from it). > But if we would just enable/disable corresponding features through > Ethtool, that would hurt XDP_PASS. Maybe it's a bad example, but > what if I want to have only RSS hash in the metadata (and don't > want to spend cycles on parsing the rest), but at the same time > still want skb path to have checksum status to not die at CPU > checksum calculation? Hmm, so this feels a little like a driver-specific optimisation? I.e., my guess is that not all drivers have a measurable overhead for pulling out the metadata. Also, once the XDP metadata bits are in place, we can move in the direction of building SKBs from the same source, so I'm not sure it's a good idea to assume that the XDP metadata is separate from what the stack consumes... In any case, if such an optimisation does turn out to be useful, we can add it later (backed by rigorous benchmarks, of course), so I think we can still start with the simple case and iterate from there? >> >> > I follow that way: >> >> > >> >> > 1) you pick a program you want to attach; >> >> > 2) usually they are written for special needs and usecases; >> >> > 3) so most likely that program will be tied with metadata/driver/etc >> >> > in some way; >> >> > 4) so you want to enable Hints of a particular format primarily for >> >> > this program and usecase, same with threshold and everything >> >> > else. >> >> > >> >> > Pls explain how you see it, I might be wrong for sure. >> >> >> >> As above: XDP hints is about giving XDP programs (and AF_XDP consumers) >> >> access to metadata that is not currently available. Tying the lifetime >> >> of that hardware configuration (i.e., which information to provide) to >> >> the lifetime of an XDP program is not a good interface: for one thing, >> >> how will it handle multiple programs? What about when XDP is not used at >> > >> > Multiple progs is stuff I didn't cover, but will do later (as you >> > all say to me, "let's start with something simple" :)). Aaaand >> > multiple XDP progs (I'm not talking about attaching progs in >> > differeng modes) is not a kernel feature, rather a libpf feature, >> > so I believe it should be handled there later... >> >> Right, but even if we don't *implement* it straight away we still need >> to take it into consideration in the design. And expecting libxdp to >> arbitrate between different XDP programs' metadata formats sounds like a >> royal PITA :) >> >> >> all but you still want to configure the same features? >> > >> > What's the point of configuring metadata when there are no progs >> > attached? To configure it once and not on every prog attach? I'm >> > not saying I don't like it, just want to clarify. >> >> See above: you turn on the features because you want the stack to >> consume them. >> >> > Maybe I need opinions from some more people, just to have an >> > overview of how most of folks see it and would like to configure >> > it. 'Cause I heard from at least one of the consumers that >> > libpf API is a perfect place for Hints to him :) >> >> Well, as a program author who wants to consume hints, you'd use >> lib{bpf,xdp} APIs to do so (probably in the form of suitable CO-RE >> macros)... >> >> >> In addition, in every other case where we do dynamic data access (with >> >> CO-RE) the BPF program is a consumer that modifies itself to access the >> >> data provided by the kernel. I get that this is harder to achieve for >> >> AF_XDP, but then let's solve that instead of making a totally >> >> inconsistent interface for XDP. >> > >> > I also see CO-RE more fitting and convenient way to use them, but >> > didn't manage to solve two things: >> > >> > 1) AF_XDP programs, so what to do with them? Prepare patches for >> > LLVM to make it able to do CO-RE on AF_XDP program load? Or >> > just hardcode them for particular usecases and NICs? What about >> > "general-purpose" programs? >> >> You provide a library to read the fields. Jesper actually already >> implemented this, did you look at his code? >> >> https://github.com/xdp-project/bpf-examples/tree/master/AF_XDP-interaction >> >> It basically builds a lookup table at load-time using BTF information >> from the kernel, keyed on BTF ID and field name, resolving them into >> offsets. It's not quite the zero-overhead of CO-RE, but it's fairly >> close and can be improved upon (CO-RE for userspace being one way of >> doing that). > > Aaaah, sorry, I completely missed that. I thought of something > similar as well, but then thought "variable field offsets, that > would annihilate optimization and performance", and our Xsk team > is super concerned about performance hits when using Hints. > >> >> > And if hardcode, what's the point then to do Generic Hints at >> > all? Then all it needs is making driver building some meta in >> > front of frames via on-off button and that's it? Why BTF ID in >> > the meta then if consumers will access meta hardcoded (via CO-RE >> > or literally hardcoded, doesn't matter)? >> >> You're quite right, we could probably implement all the access to >> existing (fixed) metadata without using any BTF at all - just define a >> common struct and some flags to designate which fields are set. In my >> mind, there are a couple of reasons for going the BTF route instead: >> >> - We can leverage CO-RE to get close to optimal efficiency in field >> access. >> >> and, more importantly: >> >> - It's infinitely extensible. With the infrastructure in place to make >> it really easy to consume metadata described by BTF, we lower the bar >> for future innovation in hardware offloads. Both for just adding new >> fixed-function stuff to hardware, but especially for fully >> programmable hardware. > > Agree :) That libxdp lookup translator fixed lots of stuff in my > mind. Great! Looks like we're slowly converging towards a shared understanding, then! :) >> > 2) In-kernel metadata consumers? Also do CO-RE? Otherwise, with no >> > generic metadata structure they won't be able to benefit from >> > Hints. But I guess we still need to provide kernel with meta? >> > Or no? >> >> In the short term, I think the "generic structure" approach is fine for >> leveraging this in the stack. Both your and Jesper's series include >> this, and I think that's totally fine. Longer term, if it turns out to >> be useful to have something more dynamic for the stack consumption as >> well, we could extend it to be CO-RE based as well (most likely by >> having the stack load a "translator" BPF program or something along >> those lines). > > Oh, that translator prog sounds nice BTW! Yeah, it's only a rough idea Jesper and I discussed at some point, but I think it could have potential (see also point above re: making XDP hints *the* source of metadata for the whole stack; wouldn't it be nice if drivers didn't have to deal with the intricacies of assembling SKBs?). -Toke
On 07/07/2022 01.22, Toke Høiland-Jørgensen wrote: > Alexander Lobakin <alexandr.lobakin@intel.com> writes: > >> From: Toke H??iland-J??rgensen <toke@redhat.com> >> Date: Tue, 05 Jul 2022 20:51:14 +0200 >> >>> Alexander Lobakin <alexandr.lobakin@intel.com> writes: >>> >>> [... snipping a bit of context here ...] >>> >>>>>>> Yeah, I'd agree this kind of configuration is something that can be >>>>>>> added later, and also it's sort of orthogonal to the consumption of the >>>>>>> metadata itself. >>>>>>> >>>>>>> Also, tying this configuration into the loading of an XDP program is a >>>>>>> terrible interface: these are hardware configuration options, let's just >>>>>>> put them into ethtool or 'ip link' like any other piece of device >>>>>>> configuration. >>>>>> >>>>>> I don't believe it fits there, especially Ethtool. Ethtool is for >>>>>> hardware configuration, XDP/AF_XDP is 95% software stuff (apart from >>>>>> offload bits which is purely NFP's for now). >>>>> >>>>> But XDP-hints is about consuming hardware features. When you're >>>>> configuring which metadata items you want, you're saying "please provide >>>>> me with these (hardware) features". So ethtool is an excellent place to >>>>> do that :) >>>> >>>> With Ethtool you configure the hardware, e.g. it won't strip VLAN >>>> tags if you disable rx-cvlan-stripping. With configuring metadata >>>> you only tell what you want to see there, don't you? >>> >>> Ah, I think we may be getting closer to identifying the disconnect >>> between our way of thinking about this! >>> >>> In my mind, there's no separate "configuration of the metadata" step. >>> You simply tell the hardware what features you want (say, "enable >>> timestamps and VLAN offload"), and the driver will then provide the >>> information related to these features in the metadata area >>> unconditionally. All XDP hints is about, then, is a way for the driver >>> to inform the rest of the system how that information is actually laid >>> out in the metadata area. >>> >>> Having a separate configuration knob to tell the driver "please lay out >>> these particular bits of metadata this way" seems like a totally >>> unnecessary (and quite complicated) feature to have when we can just let >>> the driver decide and use CO-RE to consume it? >> >> Magnus (he's currently on vacation) told me it would be useful for >> AF_XDP to enable/disable particular metadata, at least from perf >> perspective. I have recently talked to Magnus (in person at Kernel Recipes), where I tried to convey my opinion, which is: At least for existing hardware hints, we need to respect the existing Linux kernel's config interfaces, and not invent yet-another-way to configure these. (At least for now) the kernel module defined structs in C-code is the source of truth, and we consume these layouts via BTF information provided by the kernel for our XDP-hints. >> Let's say, just fetching of one "checksum ok" bit in >> the driver is faster than walking through all the descriptor words >> and driver logics (i.e. there's several hundred locs in ice which >> just parse descriptor data and build an skb or metadata from it). >> But if we would just enable/disable corresponding features through >> Ethtool, that would hurt XDP_PASS. Maybe it's a bad example, but >> what if I want to have only RSS hash in the metadata (and don't >> want to spend cycles on parsing the rest), but at the same time >> still want skb path to have checksum status to not die at CPU >> checksum calculation? > > Hmm, so this feels a little like a driver-specific optimisation? I.e., > my guess is that not all drivers have a measurable overhead for pulling > out the metadata. Also, once the XDP metadata bits are in place, we can > move in the direction of building SKBs from the same source, so I'm not > sure it's a good idea to assume that the XDP metadata is separate from > what the stack consumes... I agree. > In any case, if such an optimisation does turn out to be useful, we can > add it later (backed by rigorous benchmarks, of course), so I think we > can still start with the simple case and iterate from there? For every element in the generic hints data-structure, we already have a per-element enable/disable facilities. As they are already controlled by ethtool. Except the timestamping, which can be enabled via a sockopt. I don't see a benefit of creating another layer (of if-statements) that are also required to get the HW hint written to XDP-hints metadata area. >>>>>> I follow that way: >>>>>> >>>>>> 1) you pick a program you want to attach; >>>>>> 2) usually they are written for special needs and usecases; >>>>>> 3) so most likely that program will be tied with metadata/driver/etc >>>>>> in some way; >>>>>> 4) so you want to enable Hints of a particular format primarily for >>>>>> this program and usecase, same with threshold and everything >>>>>> else. >>>>>> >>>>>> Pls explain how you see it, I might be wrong for sure. >>>>> >>>>> As above: XDP hints is about giving XDP programs (and AF_XDP consumers) >>>>> access to metadata that is not currently available. Tying the lifetime >>>>> of that hardware configuration (i.e., which information to provide) to >>>>> the lifetime of an XDP program is not a good interface: for one thing, >>>>> how will it handle multiple programs? What about when XDP is not used at >>>> >>>> Multiple progs is stuff I didn't cover, but will do later (as you >>>> all say to me, "let's start with something simple" :)). Aaaand >>>> multiple XDP progs (I'm not talking about attaching progs in >>>> differeng modes) is not a kernel feature, rather a libpf feature, >>>> so I believe it should be handled there later... >>> >>> Right, but even if we don't *implement* it straight away we still need >>> to take it into consideration in the design. And expecting libxdp to >>> arbitrate between different XDP programs' metadata formats sounds like a >>> royal PITA :) >>> >>>>> all but you still want to configure the same features? >>>> >>>> What's the point of configuring metadata when there are no progs >>>> attached? To configure it once and not on every prog attach? I'm >>>> not saying I don't like it, just want to clarify. >>> >>> See above: you turn on the features because you want the stack to >>> consume them. >>> >>>> Maybe I need opinions from some more people, just to have an >>>> overview of how most of folks see it and would like to configure >>>> it. 'Cause I heard from at least one of the consumers that >>>> libpf API is a perfect place for Hints to him :) >>> >>> Well, as a program author who wants to consume hints, you'd use >>> lib{bpf,xdp} APIs to do so (probably in the form of suitable CO-RE >>> macros)... >>> >>>>> In addition, in every other case where we do dynamic data access (with >>>>> CO-RE) the BPF program is a consumer that modifies itself to access the >>>>> data provided by the kernel. I get that this is harder to achieve for >>>>> AF_XDP, but then let's solve that instead of making a totally >>>>> inconsistent interface for XDP. >>>> >>>> I also see CO-RE more fitting and convenient way to use them, but >>>> didn't manage to solve two things: >>>> >>>> 1) AF_XDP programs, so what to do with them? Prepare patches for >>>> LLVM to make it able to do CO-RE on AF_XDP program load? Or >>>> just hardcode them for particular usecases and NICs? What about >>>> "general-purpose" programs? >>> >>> You provide a library to read the fields. Jesper actually already >>> implemented this, did you look at his code? >>> >>> https://github.com/xdp-project/bpf-examples/tree/master/AF_XDP-interaction >>> >>> It basically builds a lookup table at load-time using BTF information >>> from the kernel, keyed on BTF ID and field name, resolving them into >>> offsets. It's not quite the zero-overhead of CO-RE, but it's fairly >>> close and can be improved upon (CO-RE for userspace being one way of >>> doing that). >> >> Aaaah, sorry, I completely missed that. I thought of something >> similar as well, but then thought "variable field offsets, that >> would annihilate optimization and performance", and our Xsk team >> is super concerned about performance hits when using Hints. >> >>> >>>> And if hardcode, what's the point then to do Generic Hints at >>>> all? Then all it needs is making driver building some meta in >>>> front of frames via on-off button and that's it? Why BTF ID in >>>> the meta then if consumers will access meta hardcoded (via CO-RE >>>> or literally hardcoded, doesn't matter)? >>> >>> You're quite right, we could probably implement all the access to >>> existing (fixed) metadata without using any BTF at all - just define a >>> common struct and some flags to designate which fields are set. In my >>> mind, there are a couple of reasons for going the BTF route instead: >>> >>> - We can leverage CO-RE to get close to optimal efficiency in field >>> access. >>> >>> and, more importantly: >>> >>> - It's infinitely extensible. With the infrastructure in place to make >>> it really easy to consume metadata described by BTF, we lower the bar >>> for future innovation in hardware offloads. Both for just adding new >>> fixed-function stuff to hardware, but especially for fully >>> programmable hardware. >> >> Agree :) That libxdp lookup translator fixed lots of stuff in my >> mind. > > Great! Looks like we're slowly converging towards a shared > understanding, then! :) > >>>> 2) In-kernel metadata consumers? Also do CO-RE? Otherwise, with no >>>> generic metadata structure they won't be able to benefit from >>>> Hints. But I guess we still need to provide kernel with meta? >>>> Or no? >>> >>> In the short term, I think the "generic structure" approach is fine for >>> leveraging this in the stack. Both your and Jesper's series include >>> this, and I think that's totally fine. Longer term, if it turns out to >>> be useful to have something more dynamic for the stack consumption as >>> well, we could extend it to be CO-RE based as well (most likely by >>> having the stack load a "translator" BPF program or something along >>> those lines). >> >> Oh, that translator prog sounds nice BTW! > > Yeah, it's only a rough idea Jesper and I discussed at some point, but I > think it could have potential (see also point above re: making XDP hints > *the* source of metadata for the whole stack; wouldn't it be nice if > drivers didn't have to deal with the intricacies of assembling SKBs?). Yes, this is the longer term goal, but we should take this in steps. (Thus, my patchset[0] focuses on the existing xdp_hints_common). Eventually (pipe-dream?), I would like to add a new BPF-hook that runs in the step converting xdp_frame to SKB (today handled in function __xdp_build_skb_from_frame). This "translator" BPF program should be tied/loaded per net_device, which makes it easier to consume the driver specific/dynamic XDP-hints layouts and BPF-code can be smaller as it only need to CO-RE handle xdp-hints structs known for this driver. Default BPF-prog should be provided and maintained by driver maintainers, but can be replaced by end-users. --Jesper [0] https://lore.kernel.org/bpf/165643378969.449467.13237011812569188299.stgit@firesoul/
On Thu, Jul 7, 2022 at 1:25 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote: > > Alexander Lobakin <alexandr.lobakin@intel.com> writes: > > > From: Toke H??iland-J??rgensen <toke@redhat.com> > > Date: Tue, 05 Jul 2022 20:51:14 +0200 > > > >> Alexander Lobakin <alexandr.lobakin@intel.com> writes: > >> > >> [... snipping a bit of context here ...] > >> > >> >> >> Yeah, I'd agree this kind of configuration is something that can be > >> >> >> added later, and also it's sort of orthogonal to the consumption of the > >> >> >> metadata itself. > >> >> >> > >> >> >> Also, tying this configuration into the loading of an XDP program is a > >> >> >> terrible interface: these are hardware configuration options, let's just > >> >> >> put them into ethtool or 'ip link' like any other piece of device > >> >> >> configuration. > >> >> > > >> >> > I don't believe it fits there, especially Ethtool. Ethtool is for > >> >> > hardware configuration, XDP/AF_XDP is 95% software stuff (apart from > >> >> > offload bits which is purely NFP's for now). > >> >> > >> >> But XDP-hints is about consuming hardware features. When you're > >> >> configuring which metadata items you want, you're saying "please provide > >> >> me with these (hardware) features". So ethtool is an excellent place to > >> >> do that :) > >> > > >> > With Ethtool you configure the hardware, e.g. it won't strip VLAN > >> > tags if you disable rx-cvlan-stripping. With configuring metadata > >> > you only tell what you want to see there, don't you? > >> > >> Ah, I think we may be getting closer to identifying the disconnect > >> between our way of thinking about this! > >> > >> In my mind, there's no separate "configuration of the metadata" step. > >> You simply tell the hardware what features you want (say, "enable > >> timestamps and VLAN offload"), and the driver will then provide the > >> information related to these features in the metadata area > >> unconditionally. All XDP hints is about, then, is a way for the driver > >> to inform the rest of the system how that information is actually laid > >> out in the metadata area. > >> > >> Having a separate configuration knob to tell the driver "please lay out > >> these particular bits of metadata this way" seems like a totally > >> unnecessary (and quite complicated) feature to have when we can just let > >> the driver decide and use CO-RE to consume it? > > > > Magnus (he's currently on vacation) told me it would be useful for > > AF_XDP to enable/disable particular metadata, at least from perf > > perspective. Let's say, just fetching of one "checksum ok" bit in > > the driver is faster than walking through all the descriptor words > > and driver logics (i.e. there's several hundred locs in ice which > > just parse descriptor data and build an skb or metadata from it). > > But if we would just enable/disable corresponding features through > > Ethtool, that would hurt XDP_PASS. Maybe it's a bad example, but > > what if I want to have only RSS hash in the metadata (and don't > > want to spend cycles on parsing the rest), but at the same time > > still want skb path to have checksum status to not die at CPU > > checksum calculation? > > Hmm, so this feels a little like a driver-specific optimisation? I.e., > my guess is that not all drivers have a measurable overhead for pulling > out the metadata. Also, once the XDP metadata bits are in place, we can > move in the direction of building SKBs from the same source, so I'm not > sure it's a good idea to assume that the XDP metadata is separate from > what the stack consumes... > > In any case, if such an optimisation does turn out to be useful, we can > add it later (backed by rigorous benchmarks, of course), so I think we > can still start with the simple case and iterate from there? Just to check if my intuition was correct or not I ran some benchmarks around this. I ported Jesper's patch set to the zero-copy driver of i40e, which was really simple thanks to Jesper's refactoring. One line of code added to the data path of the zc driver and making i40e_process_xdp_hints() a global function so it can be reached from the zc driver. I also moved the prefetch Jesper added to after the check if xdp_hints are available since it really degrades performance in the xdp_hints off case. First number is the throughput change with hints on, and the second number is with hints off. All are compared to the performance without Jesper's patch set applied. The application is xdpsock -r (which used to be part of the samples/bpf directory). Copy mode with all hints: -21% / -2% Zero-copy mode with all hints: -29% / -9% Copy mode rx timestamp only (the rest removed with an #if 0): -11% Zero-copy mode rx timestamp only: -20% So, if you only want rx timestamp, but can only enable every hint or nothing, then you get a 10% performance degradation with copy mode and 9% with zero-copy mode compared to if you were able just to enable rx timestamp alone. With these rough numbers (a real implementation would not have an #if 0) I would say it matters, but that does not mean we should not start simple and just have a big switch to start with. But as we add hints (to the same btfid), this will just get worse. Here are some other numbers I got, in case someone is interested. They are XDP numbers from xdp_rxq_info in samples/bpf. hints on / hints off XDP_DROP: -18% / -1.5% XDP_TX: -10% / -2.5% > >> >> > I follow that way: > >> >> > > >> >> > 1) you pick a program you want to attach; > >> >> > 2) usually they are written for special needs and usecases; > >> >> > 3) so most likely that program will be tied with metadata/driver/etc > >> >> > in some way; > >> >> > 4) so you want to enable Hints of a particular format primarily for > >> >> > this program and usecase, same with threshold and everything > >> >> > else. > >> >> > > >> >> > Pls explain how you see it, I might be wrong for sure. > >> >> > >> >> As above: XDP hints is about giving XDP programs (and AF_XDP consumers) > >> >> access to metadata that is not currently available. Tying the lifetime > >> >> of that hardware configuration (i.e., which information to provide) to > >> >> the lifetime of an XDP program is not a good interface: for one thing, > >> >> how will it handle multiple programs? What about when XDP is not used at > >> > > >> > Multiple progs is stuff I didn't cover, but will do later (as you > >> > all say to me, "let's start with something simple" :)). Aaaand > >> > multiple XDP progs (I'm not talking about attaching progs in > >> > differeng modes) is not a kernel feature, rather a libpf feature, > >> > so I believe it should be handled there later... > >> > >> Right, but even if we don't *implement* it straight away we still need > >> to take it into consideration in the design. And expecting libxdp to > >> arbitrate between different XDP programs' metadata formats sounds like a > >> royal PITA :) > >> > >> >> all but you still want to configure the same features? > >> > > >> > What's the point of configuring metadata when there are no progs > >> > attached? To configure it once and not on every prog attach? I'm > >> > not saying I don't like it, just want to clarify. > >> > >> See above: you turn on the features because you want the stack to > >> consume them. > >> > >> > Maybe I need opinions from some more people, just to have an > >> > overview of how most of folks see it and would like to configure > >> > it. 'Cause I heard from at least one of the consumers that > >> > libpf API is a perfect place for Hints to him :) > >> > >> Well, as a program author who wants to consume hints, you'd use > >> lib{bpf,xdp} APIs to do so (probably in the form of suitable CO-RE > >> macros)... > >> > >> >> In addition, in every other case where we do dynamic data access (with > >> >> CO-RE) the BPF program is a consumer that modifies itself to access the > >> >> data provided by the kernel. I get that this is harder to achieve for > >> >> AF_XDP, but then let's solve that instead of making a totally > >> >> inconsistent interface for XDP. > >> > > >> > I also see CO-RE more fitting and convenient way to use them, but > >> > didn't manage to solve two things: > >> > > >> > 1) AF_XDP programs, so what to do with them? Prepare patches for > >> > LLVM to make it able to do CO-RE on AF_XDP program load? Or > >> > just hardcode them for particular usecases and NICs? What about > >> > "general-purpose" programs? > >> > >> You provide a library to read the fields. Jesper actually already > >> implemented this, did you look at his code? > >> > >> https://github.com/xdp-project/bpf-examples/tree/master/AF_XDP-interaction > >> > >> It basically builds a lookup table at load-time using BTF information > >> from the kernel, keyed on BTF ID and field name, resolving them into > >> offsets. It's not quite the zero-overhead of CO-RE, but it's fairly > >> close and can be improved upon (CO-RE for userspace being one way of > >> doing that). > > > > Aaaah, sorry, I completely missed that. I thought of something > > similar as well, but then thought "variable field offsets, that > > would annihilate optimization and performance", and our Xsk team > > is super concerned about performance hits when using Hints. > > > >> > >> > And if hardcode, what's the point then to do Generic Hints at > >> > all? Then all it needs is making driver building some meta in > >> > front of frames via on-off button and that's it? Why BTF ID in > >> > the meta then if consumers will access meta hardcoded (via CO-RE > >> > or literally hardcoded, doesn't matter)? > >> > >> You're quite right, we could probably implement all the access to > >> existing (fixed) metadata without using any BTF at all - just define a > >> common struct and some flags to designate which fields are set. In my > >> mind, there are a couple of reasons for going the BTF route instead: > >> > >> - We can leverage CO-RE to get close to optimal efficiency in field > >> access. > >> > >> and, more importantly: > >> > >> - It's infinitely extensible. With the infrastructure in place to make > >> it really easy to consume metadata described by BTF, we lower the bar > >> for future innovation in hardware offloads. Both for just adding new > >> fixed-function stuff to hardware, but especially for fully > >> programmable hardware. > > > > Agree :) That libxdp lookup translator fixed lots of stuff in my > > mind. > > Great! Looks like we're slowly converging towards a shared > understanding, then! :) > > >> > 2) In-kernel metadata consumers? Also do CO-RE? Otherwise, with no > >> > generic metadata structure they won't be able to benefit from > >> > Hints. But I guess we still need to provide kernel with meta? > >> > Or no? > >> > >> In the short term, I think the "generic structure" approach is fine for > >> leveraging this in the stack. Both your and Jesper's series include > >> this, and I think that's totally fine. Longer term, if it turns out to > >> be useful to have something more dynamic for the stack consumption as > >> well, we could extend it to be CO-RE based as well (most likely by > >> having the stack load a "translator" BPF program or something along > >> those lines). > > > > Oh, that translator prog sounds nice BTW! > > Yeah, it's only a rough idea Jesper and I discussed at some point, but I > think it could have potential (see also point above re: making XDP hints > *the* source of metadata for the whole stack; wouldn't it be nice if > drivers didn't have to deal with the intricacies of assembling SKBs?). > > -Toke >
On 12/07/2022 12.33, Magnus Karlsson wrote: > On Thu, Jul 7, 2022 at 1:25 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote: >> >> Alexander Lobakin <alexandr.lobakin@intel.com> writes: >> >>> From: Toke H??iland-J??rgensen <toke@redhat.com> >>> Date: Tue, 05 Jul 2022 20:51:14 +0200 >>> >>>> Alexander Lobakin <alexandr.lobakin@intel.com> writes: >>>> >>>> [... snipping a bit of context here ...] >>>> >>>>>>>> Yeah, I'd agree this kind of configuration is something that can be >>>>>>>> added later, and also it's sort of orthogonal to the consumption of the >>>>>>>> metadata itself. >>>>>>>> >>>>>>>> Also, tying this configuration into the loading of an XDP program is a >>>>>>>> terrible interface: these are hardware configuration options, let's just >>>>>>>> put them into ethtool or 'ip link' like any other piece of device >>>>>>>> configuration. >>>>>>> >>>>>>> I don't believe it fits there, especially Ethtool. Ethtool is for >>>>>>> hardware configuration, XDP/AF_XDP is 95% software stuff (apart from >>>>>>> offload bits which is purely NFP's for now). >>>>>> >>>>>> But XDP-hints is about consuming hardware features. When you're >>>>>> configuring which metadata items you want, you're saying "please provide >>>>>> me with these (hardware) features". So ethtool is an excellent place to >>>>>> do that :) >>>>> >>>>> With Ethtool you configure the hardware, e.g. it won't strip VLAN >>>>> tags if you disable rx-cvlan-stripping. With configuring metadata >>>>> you only tell what you want to see there, don't you? >>>> >>>> Ah, I think we may be getting closer to identifying the disconnect >>>> between our way of thinking about this! >>>> >>>> In my mind, there's no separate "configuration of the metadata" step. >>>> You simply tell the hardware what features you want (say, "enable >>>> timestamps and VLAN offload"), and the driver will then provide the >>>> information related to these features in the metadata area >>>> unconditionally. All XDP hints is about, then, is a way for the driver >>>> to inform the rest of the system how that information is actually laid >>>> out in the metadata area. >>>> >>>> Having a separate configuration knob to tell the driver "please lay out >>>> these particular bits of metadata this way" seems like a totally >>>> unnecessary (and quite complicated) feature to have when we can just let >>>> the driver decide and use CO-RE to consume it? >>> >>> Magnus (he's currently on vacation) told me it would be useful for >>> AF_XDP to enable/disable particular metadata, at least from perf >>> perspective. Let's say, just fetching of one "checksum ok" bit in >>> the driver is faster than walking through all the descriptor words >>> and driver logics (i.e. there's several hundred locs in ice which >>> just parse descriptor data and build an skb or metadata from it). >>> But if we would just enable/disable corresponding features through >>> Ethtool, that would hurt XDP_PASS. Maybe it's a bad example, but >>> what if I want to have only RSS hash in the metadata (and don't >>> want to spend cycles on parsing the rest), but at the same time >>> still want skb path to have checksum status to not die at CPU >>> checksum calculation? >> >> Hmm, so this feels a little like a driver-specific optimisation? I.e., >> my guess is that not all drivers have a measurable overhead for pulling >> out the metadata. Also, once the XDP metadata bits are in place, we can >> move in the direction of building SKBs from the same source, so I'm not >> sure it's a good idea to assume that the XDP metadata is separate from >> what the stack consumes... >> >> In any case, if such an optimisation does turn out to be useful, we can >> add it later (backed by rigorous benchmarks, of course), so I think we >> can still start with the simple case and iterate from there? > > Just to check if my intuition was correct or not I ran some benchmarks > around this. I ported Jesper's patch set to the zero-copy driver of > i40e, which was really simple thanks to Jesper's refactoring. One line > of code added to the data path of the zc driver and making > i40e_process_xdp_hints() a global function so it can be reached from > the zc driver. Happy to hear it was simple to extend this to AF_XDP in the driver. Code design wise I'm trying to keep it simple for drivers to add this. I have a co-worker that have already extended ixgbe. > I also moved the prefetch Jesper added to after the > check if xdp_hints are available since it really degrades performance > in the xdp_hints off case. Good to know. > First number is the throughput change with hints on, and the second > number is with hints off. All are compared to the performance without > Jesper's patch set applied. The application is xdpsock -r (which used > to be part of the samples/bpf directory). For reviewer to relate to these numbers we need to understand/explain the extreme numbers we are dealing with. In my system with i40e and xdpsock --rx-drop I can AF_XDP drop packets with a rate of 33.633.761 pps. This corresponds to a processing time per packet: 29.7 ns (nanosec) - Calc: (1/33633761)*10^9 > Copy mode with all hints: -21% / -2% The -21% for enabling all hints does sound like an excessive overhead, but time-wise this is a reduction/overhead of 6.2 ns. The real question: Is this 6.2 ns overhead that gives us e.g. RX-checksumming lower than the gain we can obtain from avoiding doing RX-checksumming in software? - A: My previous experiments conclude[1] that for 1500 bytes frames we can save 54 ns (or increase performance with 8% for normal netstack). I was going for zero overhead when disabling xdp-hints, which is almost true as the -2% is time-wise a reduction/overhead of 0.59 ns. [1] https://github.com/xdp-project/xdp-project/blob/master/areas/core/xdp_frame01_checksum.org#measurements-compare-results--conclusion > Zero-copy mode with all hints: -29% / -9% I'm unsure why the percentages increase here, perhaps because zero-copy is faster and thus the overhead becomes a larger percentage? > Copy mode rx timestamp only (the rest removed with an #if 0): -11% > Zero-copy mode rx timestamp only: -20% > > So, if you only want rx timestamp, but can only enable every hint or > nothing, then you get a 10% performance degradation with copy mode and > 9% with zero-copy mode compared to if you were able just to enable rx > timestamp alone. With these rough numbers (a real implementation would > not have an #if 0) I would say it matters, but that does not mean we > should not start simple and just have a big switch to start with. But > as we add hints (to the same btfid), this will just get worse. IMHO we *do* already have individual enable/disable hints features via ethtool. Have you tried to use the individual ethtool switches. e.g.: ethtool -K i40e2 rx-checksumming off The i40e code uses bitfields for extracting the descriptor, which cause code that isn't optimal or fully optimized by the compiler. On my setup I gained 4.2% (or 1.24 ns) by doing this. > Here are some other numbers I got, in case someone is interested. They > are XDP numbers from xdp_rxq_info in samples/bpf. > > hints on / hints off > XDP_DROP: -18% / -1.5% My xdp_rxq_info (no-touch XDP_DROP) nanosec numbers are: hints on / hints off XDP_DROP: 35.97ns / 29.80ns (diff 6.17 ns) Maybe interesting if I touch data (via option --read), then the overhead is reduced to 4.84 ns. --Jesper > XDP_TX: -10% / -2.5% > >>>>>>> I follow that way: >>>>>>> >>>>>>> 1) you pick a program you want to attach; >>>>>>> 2) usually they are written for special needs and usecases; >>>>>>> 3) so most likely that program will be tied with metadata/driver/etc >>>>>>> in some way; >>>>>>> 4) so you want to enable Hints of a particular format primarily for >>>>>>> this program and usecase, same with threshold and everything >>>>>>> else. >>>>>>> >>>>>>> Pls explain how you see it, I might be wrong for sure. >>>>>> >>>>>> As above: XDP hints is about giving XDP programs (and AF_XDP consumers) >>>>>> access to metadata that is not currently available. Tying the lifetime >>>>>> of that hardware configuration (i.e., which information to provide) to >>>>>> the lifetime of an XDP program is not a good interface: for one thing, >>>>>> how will it handle multiple programs? What about when XDP is not used at >>>>> >>>>> Multiple progs is stuff I didn't cover, but will do later (as you >>>>> all say to me, "let's start with something simple" :)). Aaaand >>>>> multiple XDP progs (I'm not talking about attaching progs in >>>>> differeng modes) is not a kernel feature, rather a libpf feature, >>>>> so I believe it should be handled there later... >>>> >>>> Right, but even if we don't *implement* it straight away we still need >>>> to take it into consideration in the design. And expecting libxdp to >>>> arbitrate between different XDP programs' metadata formats sounds like a >>>> royal PITA :) >>>> >>>>>> all but you still want to configure the same features? >>>>> >>>>> What's the point of configuring metadata when there are no progs >>>>> attached? To configure it once and not on every prog attach? I'm >>>>> not saying I don't like it, just want to clarify. >>>> >>>> See above: you turn on the features because you want the stack to >>>> consume them. >>>> >>>>> Maybe I need opinions from some more people, just to have an >>>>> overview of how most of folks see it and would like to configure >>>>> it. 'Cause I heard from at least one of the consumers that >>>>> libpf API is a perfect place for Hints to him :) >>>> >>>> Well, as a program author who wants to consume hints, you'd use >>>> lib{bpf,xdp} APIs to do so (probably in the form of suitable CO-RE >>>> macros)... >>>> >>>>>> In addition, in every other case where we do dynamic data access (with >>>>>> CO-RE) the BPF program is a consumer that modifies itself to access the >>>>>> data provided by the kernel. I get that this is harder to achieve for >>>>>> AF_XDP, but then let's solve that instead of making a totally >>>>>> inconsistent interface for XDP. >>>>> >>>>> I also see CO-RE more fitting and convenient way to use them, but >>>>> didn't manage to solve two things: >>>>> >>>>> 1) AF_XDP programs, so what to do with them? Prepare patches for >>>>> LLVM to make it able to do CO-RE on AF_XDP program load? Or >>>>> just hardcode them for particular usecases and NICs? What about >>>>> "general-purpose" programs? >>>> >>>> You provide a library to read the fields. Jesper actually already >>>> implemented this, did you look at his code? >>>> >>>> https://github.com/xdp-project/bpf-examples/tree/master/AF_XDP-interaction >>>> >>>> It basically builds a lookup table at load-time using BTF information >>>> from the kernel, keyed on BTF ID and field name, resolving them into >>>> offsets. It's not quite the zero-overhead of CO-RE, but it's fairly >>>> close and can be improved upon (CO-RE for userspace being one way of >>>> doing that). >>> >>> Aaaah, sorry, I completely missed that. I thought of something >>> similar as well, but then thought "variable field offsets, that >>> would annihilate optimization and performance", and our Xsk team >>> is super concerned about performance hits when using Hints. >>> >>>> >>>>> And if hardcode, what's the point then to do Generic Hints at >>>>> all? Then all it needs is making driver building some meta in >>>>> front of frames via on-off button and that's it? Why BTF ID in >>>>> the meta then if consumers will access meta hardcoded (via CO-RE >>>>> or literally hardcoded, doesn't matter)? >>>> >>>> You're quite right, we could probably implement all the access to >>>> existing (fixed) metadata without using any BTF at all - just define a >>>> common struct and some flags to designate which fields are set. In my >>>> mind, there are a couple of reasons for going the BTF route instead: >>>> >>>> - We can leverage CO-RE to get close to optimal efficiency in field >>>> access. >>>> >>>> and, more importantly: >>>> >>>> - It's infinitely extensible. With the infrastructure in place to make >>>> it really easy to consume metadata described by BTF, we lower the bar >>>> for future innovation in hardware offloads. Both for just adding new >>>> fixed-function stuff to hardware, but especially for fully >>>> programmable hardware. >>> >>> Agree :) That libxdp lookup translator fixed lots of stuff in my >>> mind. >> >> Great! Looks like we're slowly converging towards a shared >> understanding, then! :) >> >>>>> 2) In-kernel metadata consumers? Also do CO-RE? Otherwise, with no >>>>> generic metadata structure they won't be able to benefit from >>>>> Hints. But I guess we still need to provide kernel with meta? >>>>> Or no? >>>> >>>> In the short term, I think the "generic structure" approach is fine for >>>> leveraging this in the stack. Both your and Jesper's series include >>>> this, and I think that's totally fine. Longer term, if it turns out to >>>> be useful to have something more dynamic for the stack consumption as >>>> well, we could extend it to be CO-RE based as well (most likely by >>>> having the stack load a "translator" BPF program or something along >>>> those lines). >>> >>> Oh, that translator prog sounds nice BTW! >> >> Yeah, it's only a rough idea Jesper and I discussed at some point, but I >> think it could have potential (see also point above re: making XDP hints >> *the* source of metadata for the whole stack; wouldn't it be nice if >> drivers didn't have to deal with the intricacies of assembling SKBs?). >> >> -Toke >> >
On Tue, Jul 12, 2022 at 4:15 PM Jesper Dangaard Brouer <jbrouer@redhat.com> wrote: > > > > On 12/07/2022 12.33, Magnus Karlsson wrote: > > On Thu, Jul 7, 2022 at 1:25 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote: > >> > >> Alexander Lobakin <alexandr.lobakin@intel.com> writes: > >> > >>> From: Toke H??iland-J??rgensen <toke@redhat.com> > >>> Date: Tue, 05 Jul 2022 20:51:14 +0200 > >>> > >>>> Alexander Lobakin <alexandr.lobakin@intel.com> writes: > >>>> > >>>> [... snipping a bit of context here ...] > >>>> > >>>>>>>> Yeah, I'd agree this kind of configuration is something that can be > >>>>>>>> added later, and also it's sort of orthogonal to the consumption of the > >>>>>>>> metadata itself. > >>>>>>>> > >>>>>>>> Also, tying this configuration into the loading of an XDP program is a > >>>>>>>> terrible interface: these are hardware configuration options, let's just > >>>>>>>> put them into ethtool or 'ip link' like any other piece of device > >>>>>>>> configuration. > >>>>>>> > >>>>>>> I don't believe it fits there, especially Ethtool. Ethtool is for > >>>>>>> hardware configuration, XDP/AF_XDP is 95% software stuff (apart from > >>>>>>> offload bits which is purely NFP's for now). > >>>>>> > >>>>>> But XDP-hints is about consuming hardware features. When you're > >>>>>> configuring which metadata items you want, you're saying "please provide > >>>>>> me with these (hardware) features". So ethtool is an excellent place to > >>>>>> do that :) > >>>>> > >>>>> With Ethtool you configure the hardware, e.g. it won't strip VLAN > >>>>> tags if you disable rx-cvlan-stripping. With configuring metadata > >>>>> you only tell what you want to see there, don't you? > >>>> > >>>> Ah, I think we may be getting closer to identifying the disconnect > >>>> between our way of thinking about this! > >>>> > >>>> In my mind, there's no separate "configuration of the metadata" step. > >>>> You simply tell the hardware what features you want (say, "enable > >>>> timestamps and VLAN offload"), and the driver will then provide the > >>>> information related to these features in the metadata area > >>>> unconditionally. All XDP hints is about, then, is a way for the driver > >>>> to inform the rest of the system how that information is actually laid > >>>> out in the metadata area. > >>>> > >>>> Having a separate configuration knob to tell the driver "please lay out > >>>> these particular bits of metadata this way" seems like a totally > >>>> unnecessary (and quite complicated) feature to have when we can just let > >>>> the driver decide and use CO-RE to consume it? > >>> > >>> Magnus (he's currently on vacation) told me it would be useful for > >>> AF_XDP to enable/disable particular metadata, at least from perf > >>> perspective. Let's say, just fetching of one "checksum ok" bit in > >>> the driver is faster than walking through all the descriptor words > >>> and driver logics (i.e. there's several hundred locs in ice which > >>> just parse descriptor data and build an skb or metadata from it). > >>> But if we would just enable/disable corresponding features through > >>> Ethtool, that would hurt XDP_PASS. Maybe it's a bad example, but > >>> what if I want to have only RSS hash in the metadata (and don't > >>> want to spend cycles on parsing the rest), but at the same time > >>> still want skb path to have checksum status to not die at CPU > >>> checksum calculation? > >> > >> Hmm, so this feels a little like a driver-specific optimisation? I.e., > >> my guess is that not all drivers have a measurable overhead for pulling > >> out the metadata. Also, once the XDP metadata bits are in place, we can > >> move in the direction of building SKBs from the same source, so I'm not > >> sure it's a good idea to assume that the XDP metadata is separate from > >> what the stack consumes... > >> > >> In any case, if such an optimisation does turn out to be useful, we can > >> add it later (backed by rigorous benchmarks, of course), so I think we > >> can still start with the simple case and iterate from there? > > > > Just to check if my intuition was correct or not I ran some benchmarks > > around this. I ported Jesper's patch set to the zero-copy driver of > > i40e, which was really simple thanks to Jesper's refactoring. One line > > of code added to the data path of the zc driver and making > > i40e_process_xdp_hints() a global function so it can be reached from > > the zc driver. > > Happy to hear it was simple to extend this to AF_XDP in the driver. > Code design wise I'm trying to keep it simple for drivers to add this. > I have a co-worker that have already extended ixgbe. > > > I also moved the prefetch Jesper added to after the > > check if xdp_hints are available since it really degrades performance > > in the xdp_hints off case. > > Good to know. > > > First number is the throughput change with hints on, and the second > > number is with hints off. All are compared to the performance without > > Jesper's patch set applied. The application is xdpsock -r (which used > > to be part of the samples/bpf directory). > > For reviewer to relate to these numbers we need to understand/explain > the extreme numbers we are dealing with. In my system with i40e and > xdpsock --rx-drop I can AF_XDP drop packets with a rate of 33.633.761 pps. > > This corresponds to a processing time per packet: 29.7 ns (nanosec) > - Calc: (1/33633761)*10^9 > > > Copy mode with all hints: -21% / -2% On my system, the overhead is 66 cycles/packet or 31 ns/packet (2.1 GHz CPU with TurboBoost disabled). Copy-mode only drops packets at a rate of 8.5 Mpps or 118 ns/packet on my system. The rate you quote must be for zero-copy as I see something similar there if I enable TurboBoost on my system. > The -21% for enabling all hints does sound like an excessive overhead, > but time-wise this is a reduction/overhead of 6.2 ns. > > The real question: Is this 6.2 ns overhead that gives us e.g. > RX-checksumming lower than the gain we can obtain from avoiding doin. > RX-checksumming in software? > - A: My previous experiments conclude[1] that for 1500 bytes frames we > can save 54 ns (or increase performance with 8% for normal netstack). If you use Rx-checksumming alone, it is a good idea for packets that are bigger than something around 500 bytes, if you use copy mode. This is a very rough estimation since I cannot mix your numbers with mine. But there is a substantial window where it pays off for sure. For ZC, this window is even larger, see below. > > I was going for zero overhead when disabling xdp-hints, which is almost > true as the -2% is time-wise a reduction/overhead of 0.59 ns. > > [1] > https://github.com/xdp-project/xdp-project/blob/master/areas/core/xdp_frame01_checksum.org#measurements-compare-results--conclusion > > > > Zero-copy mode with all hints: -29% / -9% > > I'm unsure why the percentages increase here, perhaps because zero-copy > is faster and thus the overhead becomes a larger percentage? For zero-copy, the overhead is 31 cycles/packet or 15 ns/packet on my system. I would have expected the cycles/packet overhead for copy-mode and zero-copy mode to be about the same since they use the same hints code, but it is roughly half for zero-copy. Have not examined why. The packet processing time without your patches on my system is 36 ns/packet or 27.65 Mpps for zero-copy. > > > Copy mode rx timestamp only (the rest removed with an #if 0): -11% > > Zero-copy mode rx timestamp only: -20% > > > > So, if you only want rx timestamp, but can only enable every hint or > > nothing, then you get a 10% performance degradation with copy mode and > > 9% with zero-copy mode compared to if you were able just to enable rx > > timestamp alone. With these rough numbers (a real implementation would > > not have an #if 0) I would say it matters, but that does not mean we > > should not start simple and just have a big switch to start with. But > > as we add hints (to the same btfid), this will just get worse. > > IMHO we *do* already have individual enable/disable hints features via > ethtool. > Have you tried to use the individual ethtool switches. e.g.: > > ethtool -K i40e2 rx-checksumming off > > The i40e code uses bitfields for extracting the descriptor, which cause > code that isn't optimal or fully optimized by the compiler. On my setup > I gained 4.2% (or 1.24 ns) by doing this. Forgot about that one. Will replace the bitfields and rerun the experiments to get the overhead down. > > > Here are some other numbers I got, in case someone is interested. They > > are XDP numbers from xdp_rxq_info in samples/bpf. > > > > hints on / hints off > > XDP_DROP: -18% / -1.5% > > My xdp_rxq_info (no-touch XDP_DROP) nanosec numbers are: > > hints on / hints off > XDP_DROP: 35.97ns / 29.80ns (diff 6.17 ns) > > Maybe interesting if I touch data (via option --read), then the overhead > is reduced to 4.84 ns. Good point. We should always touch the data. Will include that in the next set of experiments. > --Jesper > > > XDP_TX: -10% / -2.5% > > > >>>>>>> I follow that way: > >>>>>>> > >>>>>>> 1) you pick a program you want to attach; > >>>>>>> 2) usually they are written for special needs and usecases; > >>>>>>> 3) so most likely that program will be tied with metadata/driver/etc > >>>>>>> in some way; > >>>>>>> 4) so you want to enable Hints of a particular format primarily for > >>>>>>> this program and usecase, same with threshold and everything > >>>>>>> else. > >>>>>>> > >>>>>>> Pls explain how you see it, I might be wrong for sure. > >>>>>> > >>>>>> As above: XDP hints is about giving XDP programs (and AF_XDP consumers) > >>>>>> access to metadata that is not currently available. Tying the lifetime > >>>>>> of that hardware configuration (i.e., which information to provide) to > >>>>>> the lifetime of an XDP program is not a good interface: for one thing, > >>>>>> how will it handle multiple programs? What about when XDP is not used at > >>>>> > >>>>> Multiple progs is stuff I didn't cover, but will do later (as you > >>>>> all say to me, "let's start with something simple" :)). Aaaand > >>>>> multiple XDP progs (I'm not talking about attaching progs in > >>>>> differeng modes) is not a kernel feature, rather a libpf feature, > >>>>> so I believe it should be handled there later... > >>>> > >>>> Right, but even if we don't *implement* it straight away we still need > >>>> to take it into consideration in the design. And expecting libxdp to > >>>> arbitrate between different XDP programs' metadata formats sounds like a > >>>> royal PITA :) > >>>> > >>>>>> all but you still want to configure the same features? > >>>>> > >>>>> What's the point of configuring metadata when there are no progs > >>>>> attached? To configure it once and not on every prog attach? I'm > >>>>> not saying I don't like it, just want to clarify. > >>>> > >>>> See above: you turn on the features because you want the stack to > >>>> consume them. > >>>> > >>>>> Maybe I need opinions from some more people, just to have an > >>>>> overview of how most of folks see it and would like to configure > >>>>> it. 'Cause I heard from at least one of the consumers that > >>>>> libpf API is a perfect place for Hints to him :) > >>>> > >>>> Well, as a program author who wants to consume hints, you'd use > >>>> lib{bpf,xdp} APIs to do so (probably in the form of suitable CO-RE > >>>> macros)... > >>>> > >>>>>> In addition, in every other case where we do dynamic data access (with > >>>>>> CO-RE) the BPF program is a consumer that modifies itself to access the > >>>>>> data provided by the kernel. I get that this is harder to achieve for > >>>>>> AF_XDP, but then let's solve that instead of making a totally > >>>>>> inconsistent interface for XDP. > >>>>> > >>>>> I also see CO-RE more fitting and convenient way to use them, but > >>>>> didn't manage to solve two things: > >>>>> > >>>>> 1) AF_XDP programs, so what to do with them? Prepare patches for > >>>>> LLVM to make it able to do CO-RE on AF_XDP program load? Or > >>>>> just hardcode them for particular usecases and NICs? What about > >>>>> "general-purpose" programs? > >>>> > >>>> You provide a library to read the fields. Jesper actually already > >>>> implemented this, did you look at his code? > >>>> > >>>> https://github.com/xdp-project/bpf-examples/tree/master/AF_XDP-interaction > >>>> > >>>> It basically builds a lookup table at load-time using BTF information > >>>> from the kernel, keyed on BTF ID and field name, resolving them into > >>>> offsets. It's not quite the zero-overhead of CO-RE, but it's fairly > >>>> close and can be improved upon (CO-RE for userspace being one way of > >>>> doing that). > >>> > >>> Aaaah, sorry, I completely missed that. I thought of something > >>> similar as well, but then thought "variable field offsets, that > >>> would annihilate optimization and performance", and our Xsk team > >>> is super concerned about performance hits when using Hints. > >>> > >>>> > >>>>> And if hardcode, what's the point then to do Generic Hints at > >>>>> all? Then all it needs is making driver building some meta in > >>>>> front of frames via on-off button and that's it? Why BTF ID in > >>>>> the meta then if consumers will access meta hardcoded (via CO-RE > >>>>> or literally hardcoded, doesn't matter)? > >>>> > >>>> You're quite right, we could probably implement all the access to > >>>> existing (fixed) metadata without using any BTF at all - just define a > >>>> common struct and some flags to designate which fields are set. In my > >>>> mind, there are a couple of reasons for going the BTF route instead: > >>>> > >>>> - We can leverage CO-RE to get close to optimal efficiency in field > >>>> access. > >>>> > >>>> and, more importantly: > >>>> > >>>> - It's infinitely extensible. With the infrastructure in place to make > >>>> it really easy to consume metadata described by BTF, we lower the bar > >>>> for future innovation in hardware offloads. Both for just adding new > >>>> fixed-function stuff to hardware, but especially for fully > >>>> programmable hardware. > >>> > >>> Agree :) That libxdp lookup translator fixed lots of stuff in my > >>> mind. > >> > >> Great! Looks like we're slowly converging towards a shared > >> understanding, then! :) > >> > >>>>> 2) In-kernel metadata consumers? Also do CO-RE? Otherwise, with no > >>>>> generic metadata structure they won't be able to benefit from > >>>>> Hints. But I guess we still need to provide kernel with meta? > >>>>> Or no? > >>>> > >>>> In the short term, I think the "generic structure" approach is fine for > >>>> leveraging this in the stack. Both your and Jesper's series include > >>>> this, and I think that's totally fine. Longer term, if it turns out to > >>>> be useful to have something more dynamic for the stack consumption as > >>>> well, we could extend it to be CO-RE based as well (most likely by > >>>> having the stack load a "translator" BPF program or something along > >>>> those lines). > >>> > >>> Oh, that translator prog sounds nice BTW! > >> > >> Yeah, it's only a rough idea Jesper and I discussed at some point, but I > >> think it could have potential (see also point above re: making XDP hints > >> *the* source of metadata for the whole stack; wouldn't it be nice if > >> drivers didn't have to deal with the intricacies of assembling SKBs?). > >> > >> -Toke > >> > > >
This RFC is to give the whole picture. It will most likely be split onto several series, maybe even merge cycles. See the "table of contents" below. The series adds ability to pass different frame details/parameters/parameters used by most of NICs and the kernel stack (in skbs), not essential, but highly wanted, such as: * checksum value, status (Rx) or command (Tx); * hash value and type/level (Rx); * queue number (Rx); * timestamps; * and so on. As XDP structures used to represent frames are as small as possible and must stay like that, it is done by using the already existing concept of metadata, i.e. some space right before a frame where BPF programs can put arbitrary data. Now, a NIC driver, or even a SmartNIC itself, can put those params there in a well-defined format. The format is fixed, but can be of several different types represented by structures, which definitions are available to the kernel, BPF programs and the userland. It is fixed due to it being almost a UAPI, and the exact format can be determined by reading the last 10 bytes of metadata. They contain a 2-byte magic ID to not confuse it with a non-compatible meta and a 8-byte combined BTF ID + type ID: the ID of the BTF where this structure is defined and the ID of that definition inside that BTF. Users can obtain BTF IDs by structure types using helpers available in the kernel, BPF (written by the CO-RE/verifier) and the userland (libbpf -> kernel call) and then rely on those ID when reading data to make sure whether they support it and what to do with it. Why separate magic and ID? The idea is to make different formats always contain the basic/"generic" structure embedded at the end. This way we can still benefit in purely generic consumers (like cpumap) while providing some "extra" data to those who support it. The enablement of this feature is controlled on attaching/replacing XDP program on an interface with two new parameters: that combined BTF+type ID and metadata threshold. The threshold specifies the minimum frame size which a driver (or NIC) should start composing metadata from. It is introduced instead of just false/true flag due to that often it's not worth it to spend cycles to fetch all that data for such small frames: let's say, it can be even faster to just calculate checksums for them on CPU rather than touch non-coherent DMA zone. Simple XDP_DROP case loses 15 Mpps on 64 byte frames with enabled metadata, threshold can help mitigate that. The RFC can be divided into 8 parts: 01-04: BTF ID hacking: here Larysa provides BPF programs with not only type ID, but the ID of the BTF as well by using the unused upper 32 bits. 05-10: this provides in-kernel mechanisms for taking ID and threshold from the userspace and passing it to the drivers. 11-18: provides libbpf API to be able to specify those params from the userspace, plus some small selftest to verify that both the kernel and the userspace parts work. 19-29: here the actual structure is defined, then the in-kernel helpers and finally here comes the first consumer: function used to convert &xdp_frame to &sk_buff now will be trying to parse metadata. The affected users are cpumap and veth. 30-36: here I try to benefit from the metadata in cpumap even more by switching it to GRO. Now that we have checksums from NIC available... but even with no meta it gives some fair improvements. 37-43: enabling building generic metadata on Generic/skb path. Since skbs already have all those fields, it's not a problem to do this in here, plus allows to benefit from it on interfaces not supporting meta yet. 44-47: ice driver part, including enabling prog hot-swap; 48-52: adds a complex selftest to verify everything works. Can be used as a sample as well, showing how to work with metadata in BPF programs and how to configure it from the userspace. Please refer to the actual commit messages where some precise implementation details might be explained. Nearly 20 of 52 are various cleanups and prereqs, as usually. Perf figures were taken on cpumap redirect from the ice interface (driver-side XDP), redirecting the traffic within the same node. Frame size / 64/42 128/20 256/8 512/4 1024/2 1532/1 thread num meta off 30022 31350 21993 12144 6374 3610 meta on 33059 28502 21503 12146 6380 3610 GRO meta off 30020 31822 21970 12145 6384 3610 GRO meta on 34736 28848 21566 12144 6381 3610 Yes, redirect between the nodes plays awfully with the metadata composed by the driver: meta off 21449 18078 16897 11820 6383 3610 meta on 16956 19004 14337 8228 5683 2822 GRO meta off 22539 19129 16304 11659 6381 3592 GRO meta on 17047 20366 15435 8878 5600 2753 Questions still open: * the actual generic structure: it must have all the fields used oftenly and by the majority of NICs. It can always be expanded later on (note that the structure grows to the left), but the less often UAPI is modified, the better (less compat pain); * ability to specify the exact fields to fill by the driver, e.g. flags bitmap passed from the userspace. In theory it can be more optimal to not spend cycles on data we don't need, but at the same time increases the complexity of the whole concept (e.g. it will be more problematic to unify drivers' routines for collecting data from descriptors to metadata and to skbs); * there was an idea to be able to specify from the userspace the desired cacheline offset, so that [the wanted fields of] metadata and the packet headers would lay in the same CL. Can't be implemented in Generic/skb XDP and ice has some troubles with it too; * lacks AF_XDP/XSk perf numbers and different other scenarios in general, is the current implementation optimal for them? * metadata threshold and everything else present in this implementation. The RFC is also available on my open GitHub[0]. Merry and long review and discussion, enjoy! [0] https://github.com/alobakin/linux/tree/xdp_hints Alexander Lobakin (46): libbpf: add function to get the pair BTF ID + type ID for a given type net, xdp: decouple XDP code from the core networking code bpf: pass a pointer to union bpf_attr to bpf_link_ops::update_prog() net, xdp: remove redundant arguments from dev_xdp_{at,de}tach_link() net, xdp: factor out XDP install arguments to a separate structure net, xdp: add ability to specify BTF ID for XDP metadata net, xdp: add ability to specify frame size threshold for XDP metadata libbpf: factor out __bpf_set_link_xdp_fd_replace() args into a struct libbpf: add ability to set the BTF/type ID on setting XDP prog libbpf: add ability to set the meta threshold on setting XDP prog libbpf: pass &bpf_link_create_opts directly to bpf_program__attach_fd() libbpf: add bpf_program__attach_xdp_opts() selftests/bpf: expand xdp_link to check that setting meta opts works samples/bpf: pass a struct to sample_install_xdp() samples/bpf: add ability to specify metadata threshold stddef: make __struct_group() UAPI C++-friendly net, xdp: move XDP metadata helpers into new xdp_meta.h net, xdp: allow metadata > 32 net, skbuff: add ability to skip skb metadata comparison net, skbuff: constify the @skb argument of skb_hwtstamps() net, xdp: add basic generic metadata accessors bpf, btf: add a pair of function to work with the BTF ID + type ID pair net, xdp: add &sk_buff <-> &xdp_meta_generic converters net, xdp: prefetch data a bit when building an skb from an &xdp_frame net, xdp: try to fill skb fields when converting from an &xdp_frame net, gro: decouple GRO from the NAPI layer net, gro: expose some GRO API to use outside of NAPI bpf, cpumap: switch to GRO from netif_receive_skb_list() bpf, cpumap: add option to set a timeout for deferred flush samples/bpf: add 'timeout' option to xdp_redirect_cpu net, skbuff: introduce napi_skb_cache_get_bulk() bpf, cpumap: switch to napi_skb_cache_get_bulk() rcupdate: fix access helpers for incomplete struct pointers on GCC < 10 net, xdp: remove unused xdp_attachment_info::flags net, xdp: make &xdp_attachment_info a bit more useful in drivers net, xdp: add an RCU version of xdp_attachment_setup() net, xdp: replace net_device::xdp_prog pointer with &xdp_attachment_info net, xdp: shortcut skb->dev in bpf_prog_run_generic_xdp() net, xdp: build XDP generic metadata on Generic (skb) XDP path net, ice: allow XDP prog hot-swapping net, ice: consolidate all skb fields processing net, ice: use an onstack &xdp_meta_generic_rx to store HW frame info net, ice: build XDP generic metadata libbpf: compress Endianness ops with a macro selftests/bpf: fix using test_xdp_meta BPF prog via skeleton infra selftests/bpf: add XDP Generic Hints selftest Larysa Zaremba (5): libbpf: factor out BTF loading from load_module_btfs() libbpf: try to load vmlinux BTF from the kernel first libbpf: patch module BTF ID into BPF insns libbpf: add LE <--> CPU conversion helpers libbpf: introduce a couple memory access helpers Michal Swiatkowski (1): bpf, xdp: declare generic XDP metadata structure MAINTAINERS | 5 +- drivers/net/ethernet/brocade/bna/bnad.c | 1 + drivers/net/ethernet/cortina/gemini.c | 1 + drivers/net/ethernet/intel/ice/ice.h | 16 +- drivers/net/ethernet/intel/ice/ice_lib.c | 4 +- drivers/net/ethernet/intel/ice/ice_main.c | 79 +- drivers/net/ethernet/intel/ice/ice_ptp.c | 19 +- drivers/net/ethernet/intel/ice/ice_ptp.h | 17 +- drivers/net/ethernet/intel/ice/ice_txrx.c | 51 +- drivers/net/ethernet/intel/ice/ice_txrx.h | 3 +- drivers/net/ethernet/intel/ice/ice_txrx_lib.c | 154 +-- drivers/net/ethernet/intel/ice/ice_txrx_lib.h | 88 +- drivers/net/ethernet/intel/ice/ice_xsk.c | 26 +- .../ethernet/mellanox/mlx5/core/en/xsk/rx.c | 1 + drivers/net/ethernet/netronome/nfp/nfd3/xsk.c | 1 + drivers/net/tun.c | 2 +- include/linux/bpf.h | 3 +- include/linux/btf.h | 13 + include/linux/filter.h | 2 + include/linux/netdevice.h | 41 +- include/linux/rcupdate.h | 37 +- include/linux/skbuff.h | 35 +- include/net/gro.h | 53 +- include/net/xdp.h | 34 +- include/net/xdp_meta.h | 398 ++++++++ include/uapi/linux/bpf.h | 194 ++++ include/uapi/linux/if_link.h | 2 + include/uapi/linux/stddef.h | 12 +- kernel/bpf/bpf_iter.c | 1 + kernel/bpf/btf.c | 133 ++- kernel/bpf/cgroup.c | 4 +- kernel/bpf/cpumap.c | 80 +- kernel/bpf/net_namespace.c | 1 + kernel/bpf/syscall.c | 4 +- net/bpf/Makefile | 5 +- net/{core/xdp.c => bpf/core.c} | 214 +++- net/bpf/dev.c | 871 +++++++++++++++++ net/bpf/prog_ops.c | 912 ++++++++++++++++++ net/bpf/test_run.c | 2 +- net/core/Makefile | 2 +- net/core/dev.c | 869 +---------------- net/core/dev.h | 4 - net/core/filter.c | 883 +---------------- net/core/gro.c | 120 ++- net/core/rtnetlink.c | 24 +- net/core/skbuff.c | 44 + net/packet/af_packet.c | 8 +- net/xdp/xsk.c | 2 +- samples/bpf/xdp_redirect_cpu_user.c | 44 +- samples/bpf/xdp_redirect_map_multi_user.c | 26 +- samples/bpf/xdp_redirect_map_user.c | 22 +- samples/bpf/xdp_redirect_user.c | 21 +- samples/bpf/xdp_router_ipv4_user.c | 20 +- samples/bpf/xdp_sample_user.c | 38 +- samples/bpf/xdp_sample_user.h | 11 +- tools/include/uapi/linux/bpf.h | 194 ++++ tools/include/uapi/linux/if_link.h | 2 + tools/include/uapi/linux/stddef.h | 50 + tools/lib/bpf/bpf.c | 22 + tools/lib/bpf/bpf.h | 22 +- tools/lib/bpf/bpf_core_read.h | 3 +- tools/lib/bpf/bpf_endian.h | 56 +- tools/lib/bpf/bpf_helpers.h | 64 ++ tools/lib/bpf/btf.c | 142 ++- tools/lib/bpf/libbpf.c | 201 +++- tools/lib/bpf/libbpf.h | 30 +- tools/lib/bpf/libbpf.map | 2 + tools/lib/bpf/libbpf_internal.h | 7 +- tools/lib/bpf/netlink.c | 81 +- tools/lib/bpf/relo_core.c | 8 +- tools/lib/bpf/relo_core.h | 1 + tools/testing/selftests/bpf/.gitignore | 1 + tools/testing/selftests/bpf/Makefile | 4 +- .../selftests/bpf/prog_tests/xdp_link.c | 30 +- .../selftests/bpf/progs/test_xdp_meta.c | 40 +- tools/testing/selftests/bpf/test_xdp_meta.c | 294 ++++++ tools/testing/selftests/bpf/test_xdp_meta.sh | 59 +- 77 files changed, 4758 insertions(+), 2212 deletions(-) create mode 100644 include/net/xdp_meta.h rename net/{core/xdp.c => bpf/core.c} (73%) create mode 100644 net/bpf/dev.c create mode 100644 net/bpf/prog_ops.c create mode 100644 tools/include/uapi/linux/stddef.h create mode 100644 tools/testing/selftests/bpf/test_xdp_meta.c -- 2.36.1