| Message ID | 20230703181226.19380-16-larysa.zaremba@intel.com (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | BPF |
| Headers | show |
| Series | XDP metadata via kfuncs for ice | expand |
Larysa Zaremba wrote: > From: Aleksander Lobakin <aleksander.lobakin@intel.com> > > When using XDP hints, metadata sometimes has to be much bigger > than 32 bytes. Relax the restriction, allow metadata larger than 32 bytes > and make __skb_metadata_differs() work with bigger lengths. > > Now size of metadata is only limited by the fact it is stored as u8 > in skb_shared_info, so maximum possible value is 255. Other important > conditions, such as having enough space for xdp_frame building, are already > checked in bpf_xdp_adjust_meta(). > > The requirement of having its length aligned to 4 bytes is still > valid. > > Signed-off-by: Aleksander Lobakin <aleksander.lobakin@intel.com> > Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com> > --- > include/linux/skbuff.h | 13 ++++++++----- > include/net/xdp.h | 7 ++++++- > 2 files changed, 14 insertions(+), 6 deletions(-) > > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h > index 91ed66952580..cd49cdd71019 100644 > --- a/include/linux/skbuff.h > +++ b/include/linux/skbuff.h > @@ -4209,10 +4209,13 @@ static inline bool __skb_metadata_differs(const struct sk_buff *skb_a, > { > const void *a = skb_metadata_end(skb_a); > const void *b = skb_metadata_end(skb_b); > - /* Using more efficient varaiant than plain call to memcmp(). */ > -#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) && BITS_PER_LONG == 64 Why are we removing the ifdef here? Its adding a runtime 'if' when its not necessary. I would keep the ifdef and simply add the default case in the switch.
On Mon, Jul 03, 2023 at 02:06:46PM -0700, John Fastabend wrote: > Larysa Zaremba wrote: > > From: Aleksander Lobakin <aleksander.lobakin@intel.com> > > > > When using XDP hints, metadata sometimes has to be much bigger > > than 32 bytes. Relax the restriction, allow metadata larger than 32 bytes > > and make __skb_metadata_differs() work with bigger lengths. > > > > Now size of metadata is only limited by the fact it is stored as u8 > > in skb_shared_info, so maximum possible value is 255. Other important > > conditions, such as having enough space for xdp_frame building, are already > > checked in bpf_xdp_adjust_meta(). > > > > The requirement of having its length aligned to 4 bytes is still > > valid. > > > > Signed-off-by: Aleksander Lobakin <aleksander.lobakin@intel.com> > > Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com> > > --- > > include/linux/skbuff.h | 13 ++++++++----- > > include/net/xdp.h | 7 ++++++- > > 2 files changed, 14 insertions(+), 6 deletions(-) > > > > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h > > index 91ed66952580..cd49cdd71019 100644 > > --- a/include/linux/skbuff.h > > +++ b/include/linux/skbuff.h > > @@ -4209,10 +4209,13 @@ static inline bool __skb_metadata_differs(const struct sk_buff *skb_a, > > { > > const void *a = skb_metadata_end(skb_a); > > const void *b = skb_metadata_end(skb_b); > > - /* Using more efficient varaiant than plain call to memcmp(). */ > > -#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) && BITS_PER_LONG == 64 > > Why are we removing the ifdef here? Its adding a runtime 'if' when its not > necessary. I would keep the ifdef and simply add the default case > in the switch. Seems like Alex has missed your message, but we discussed this with him before, so I know the answer: Compiler will 100% convert it into a compile-time 'if' and this looks nicer than preprocessor condition.
From: Larysa Zaremba <larysa.zaremba@intel.com> Date: Thu, 6 Jul 2023 16:51:22 +0200 > On Mon, Jul 03, 2023 at 02:06:46PM -0700, John Fastabend wrote: >> Larysa Zaremba wrote: >>> From: Aleksander Lobakin <aleksander.lobakin@intel.com> >>> >>> When using XDP hints, metadata sometimes has to be much bigger >>> than 32 bytes. Relax the restriction, allow metadata larger than 32 bytes >>> and make __skb_metadata_differs() work with bigger lengths. >>> >>> Now size of metadata is only limited by the fact it is stored as u8 >>> in skb_shared_info, so maximum possible value is 255. Other important >>> conditions, such as having enough space for xdp_frame building, are already >>> checked in bpf_xdp_adjust_meta(). >>> >>> The requirement of having its length aligned to 4 bytes is still >>> valid. >>> >>> Signed-off-by: Aleksander Lobakin <aleksander.lobakin@intel.com> >>> Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com> >>> --- >>> include/linux/skbuff.h | 13 ++++++++----- >>> include/net/xdp.h | 7 ++++++- >>> 2 files changed, 14 insertions(+), 6 deletions(-) >>> >>> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h >>> index 91ed66952580..cd49cdd71019 100644 >>> --- a/include/linux/skbuff.h >>> +++ b/include/linux/skbuff.h >>> @@ -4209,10 +4209,13 @@ static inline bool __skb_metadata_differs(const struct sk_buff *skb_a, >>> { >>> const void *a = skb_metadata_end(skb_a); >>> const void *b = skb_metadata_end(skb_b); >>> - /* Using more efficient varaiant than plain call to memcmp(). */ >>> -#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) && BITS_PER_LONG == 64 >> >> Why are we removing the ifdef here? Its adding a runtime 'if' when its not >> necessary. I would keep the ifdef and simply add the default case >> in the switch. > > Seems like Alex has missed your message, but we discussed this with him before, > so I know the answer: Compiler will 100% convert it into a compile-time 'if' and > this looks nicer than preprocessor condition. Sorry, I'm not always able to follow all the threads =\ As Larysa said, it's not a runtime `if`. Both conditions are always known at compilation time. And this looks a bit less ugly than with ifdefs to me :D Thanks, Olek
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 91ed66952580..cd49cdd71019 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -4209,10 +4209,13 @@ static inline bool __skb_metadata_differs(const struct sk_buff *skb_a, { const void *a = skb_metadata_end(skb_a); const void *b = skb_metadata_end(skb_b); - /* Using more efficient varaiant than plain call to memcmp(). */ -#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) && BITS_PER_LONG == 64 u64 diffs = 0; + if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) || + BITS_PER_LONG != 64) + goto slow; + + /* Using more efficient variant than plain call to memcmp(). */ switch (meta_len) { #define __it(x, op) (x -= sizeof(u##op)) #define __it_diff(a, b, op) (*(u##op *)__it(a, op)) ^ (*(u##op *)__it(b, op)) @@ -4232,11 +4235,11 @@ static inline bool __skb_metadata_differs(const struct sk_buff *skb_a, fallthrough; case 4: diffs |= __it_diff(a, b, 32); break; + default: +slow: + return memcmp(a - meta_len, b - meta_len, meta_len); } return diffs; -#else - return memcmp(a - meta_len, b - meta_len, meta_len); -#endif } static inline bool skb_metadata_differs(const struct sk_buff *skb_a, diff --git a/include/net/xdp.h b/include/net/xdp.h index 61ed38fa79d1..3008042a00e3 100644 --- a/include/net/xdp.h +++ b/include/net/xdp.h @@ -370,7 +370,12 @@ xdp_data_meta_unsupported(const struct xdp_buff *xdp) static inline bool xdp_metalen_invalid(unsigned long metalen) { - return (metalen & (sizeof(__u32) - 1)) || (metalen > 32); + typeof(metalen) meta_max; + + meta_max = type_max(typeof_member(struct skb_shared_info, meta_len)); + BUILD_BUG_ON(!__builtin_constant_p(meta_max)); + + return !IS_ALIGNED(metalen, sizeof(u32)) || metalen > meta_max; } struct xdp_attachment_info {