| Message ID | 20181105085820.6341-1-aaron.lu@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/2] mm/page_alloc: free order-0 pages through PCP in page_frag_free() | expand |
On 11/5/18 9:58 AM, Aaron Lu wrote: > page_frag_free() calls __free_pages_ok() to free the page back to > Buddy. This is OK for high order page, but for order-0 pages, it > misses the optimization opportunity of using Per-Cpu-Pages and can > cause zone lock contention when called frequently. > > Paweł Staszewski recently shared his result of 'how Linux kernel > handles normal traffic'[1] and from perf data, Jesper Dangaard Brouer > found the lock contention comes from page allocator: > > mlx5e_poll_tx_cq > | > --16.34%--napi_consume_skb > | > |--12.65%--__free_pages_ok > | | > | --11.86%--free_one_page > | | > | |--10.10%--queued_spin_lock_slowpath > | | > | --0.65%--_raw_spin_lock > | > |--1.55%--page_frag_free > | > --1.44%--skb_release_data > > Jesper explained how it happened: mlx5 driver RX-page recycle > mechanism is not effective in this workload and pages have to go > through the page allocator. The lock contention happens during > mlx5 DMA TX completion cycle. And the page allocator cannot keep > up at these speeds.[2] > > I thought that __free_pages_ok() are mostly freeing high order > pages and thought this is an lock contention for high order pages > but Jesper explained in detail that __free_pages_ok() here are > actually freeing order-0 pages because mlx5 is using order-0 pages > to satisfy its page pool allocation request.[3] > > The free path as pointed out by Jesper is: > skb_free_head() > -> skb_free_frag() > -> skb_free_frag() > -> page_frag_free() > And the pages being freed on this path are order-0 pages. > > Fix this by doing similar things as in __page_frag_cache_drain() - > send the being freed page to PCP if it's an order-0 page, or > directly to Buddy if it is a high order page. > > With this change, Paweł hasn't noticed lock contention yet in > his workload and Jesper has noticed a 7% performance improvement > using a micro benchmark and lock contention is gone. > > [1]: https://www.spinics.net/lists/netdev/msg531362.html > [2]: https://www.spinics.net/lists/netdev/msg531421.html > [3]: https://www.spinics.net/lists/netdev/msg531556.html > Reported-by: Paweł Staszewski <pstaszewski@itcare.pl> > Analysed-by: Jesper Dangaard Brouer <brouer@redhat.com> > Signed-off-by: Aaron Lu <aaron.lu@intel.com> Yeah looks like an obvious thing to do. Acked-by: Vlastimil Babka <vbabka@suse.cz> > --- > mm/page_alloc.c | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index ae31839874b8..91a9a6af41a2 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4555,8 +4555,14 @@ void page_frag_free(void *addr) > { > struct page *page = virt_to_head_page(addr); > > - if (unlikely(put_page_testzero(page))) > - __free_pages_ok(page, compound_order(page)); > + if (unlikely(put_page_testzero(page))) { > + unsigned int order = compound_order(page); > + > + if (order == 0) > + free_unref_page(page); > + else > + __free_pages_ok(page, order); > + } > } > EXPORT_SYMBOL(page_frag_free); > >
On Mon, Nov 05, 2018 at 04:58:19PM +0800, Aaron Lu wrote: > page_frag_free() calls __free_pages_ok() to free the page back to > Buddy. This is OK for high order page, but for order-0 pages, it > misses the optimization opportunity of using Per-Cpu-Pages and can > cause zone lock contention when called frequently. > > [1]: https://www.spinics.net/lists/netdev/msg531362.html > [2]: https://www.spinics.net/lists/netdev/msg531421.html > [3]: https://www.spinics.net/lists/netdev/msg531556.html > Reported-by: PaweÅ Staszewski <pstaszewski@itcare.pl> > Analysed-by: Jesper Dangaard Brouer <brouer@redhat.com> > Signed-off-by: Aaron Lu <aaron.lu@intel.com> Well spotted, Acked-by: Mel Gorman <mgorman@techsingularity.net>
On Mon, 5 Nov 2018 16:58:19 +0800 Aaron Lu <aaron.lu@intel.com> wrote: > page_frag_free() calls __free_pages_ok() to free the page back to > Buddy. This is OK for high order page, but for order-0 pages, it > misses the optimization opportunity of using Per-Cpu-Pages and can > cause zone lock contention when called frequently. > > Paweł Staszewski recently shared his result of 'how Linux kernel > handles normal traffic'[1] and from perf data, Jesper Dangaard Brouer > found the lock contention comes from page allocator: > > mlx5e_poll_tx_cq > | > --16.34%--napi_consume_skb > | > |--12.65%--__free_pages_ok > | | > | --11.86%--free_one_page > | | > | |--10.10%--queued_spin_lock_slowpath > | | > | --0.65%--_raw_spin_lock > | > |--1.55%--page_frag_free > | > --1.44%--skb_release_data > > Jesper explained how it happened: mlx5 driver RX-page recycle > mechanism is not effective in this workload and pages have to go > through the page allocator. The lock contention happens during > mlx5 DMA TX completion cycle. And the page allocator cannot keep > up at these speeds.[2] > > I thought that __free_pages_ok() are mostly freeing high order > pages and thought this is an lock contention for high order pages > but Jesper explained in detail that __free_pages_ok() here are > actually freeing order-0 pages because mlx5 is using order-0 pages > to satisfy its page pool allocation request.[3] > > The free path as pointed out by Jesper is: > skb_free_head() > -> skb_free_frag() > -> skb_free_frag() Nitpick: you added skb_free_frag() two times, else correct. (All this stuff gets inlined by the compiler, which makes it hard to spot with perf report). > -> page_frag_free() > And the pages being freed on this path are order-0 pages. > > Fix this by doing similar things as in __page_frag_cache_drain() - > send the being freed page to PCP if it's an order-0 page, or > directly to Buddy if it is a high order page. > > With this change, Paweł hasn't noticed lock contention yet in > his workload and Jesper has noticed a 7% performance improvement > using a micro benchmark and lock contention is gone. > > [1]: https://www.spinics.net/lists/netdev/msg531362.html > [2]: https://www.spinics.net/lists/netdev/msg531421.html > [3]: https://www.spinics.net/lists/netdev/msg531556.html > Reported-by: Paweł Staszewski <pstaszewski@itcare.pl> > Analysed-by: Jesper Dangaard Brouer <brouer@redhat.com> > Signed-off-by: Aaron Lu <aaron.lu@intel.com> > --- It is REALLY great that Aaron spotted this! (based on my analysis). This have likely been causing scalability issues on real-life network traffic, but have been hiding behind the driver level recycle tricks for micro-benchmarking. Acked-by: Jesper Dangaard Brouer <brouer@redhat.com> > mm/page_alloc.c | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index ae31839874b8..91a9a6af41a2 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4555,8 +4555,14 @@ void page_frag_free(void *addr) > { > struct page *page = virt_to_head_page(addr); > > - if (unlikely(put_page_testzero(page))) > - __free_pages_ok(page, compound_order(page)); > + if (unlikely(put_page_testzero(page))) { > + unsigned int order = compound_order(page); > + > + if (order == 0) > + free_unref_page(page); > + else > + __free_pages_ok(page, order); > + } > } > EXPORT_SYMBOL(page_frag_free); >
Hi Aaron, > page_frag_free() calls __free_pages_ok() to free the page back to > Buddy. This is OK for high order page, but for order-0 pages, it > misses the optimization opportunity of using Per-Cpu-Pages and can > cause zone lock contention when called frequently. > > Paweł Staszewski recently shared his result of 'how Linux kernel > handles normal traffic'[1] and from perf data, Jesper Dangaard Brouer > found the lock contention comes from page allocator: > > mlx5e_poll_tx_cq > | > --16.34%--napi_consume_skb > | > |--12.65%--__free_pages_ok > | | > | --11.86%--free_one_page > | | > | |--10.10%--queued_spin_lock_slowpath > | | > | --0.65%--_raw_spin_lock > | > |--1.55%--page_frag_free > | > --1.44%--skb_release_data > > Jesper explained how it happened: mlx5 driver RX-page recycle > mechanism is not effective in this workload and pages have to go > through the page allocator. The lock contention happens during > mlx5 DMA TX completion cycle. And the page allocator cannot keep > up at these speeds.[2] > > I thought that __free_pages_ok() are mostly freeing high order > pages and thought this is an lock contention for high order pages > but Jesper explained in detail that __free_pages_ok() here are > actually freeing order-0 pages because mlx5 is using order-0 pages > to satisfy its page pool allocation request.[3] > > The free path as pointed out by Jesper is: > skb_free_head() > -> skb_free_frag() > -> skb_free_frag() > -> page_frag_free() > And the pages being freed on this path are order-0 pages. > > Fix this by doing similar things as in __page_frag_cache_drain() - > send the being freed page to PCP if it's an order-0 page, or > directly to Buddy if it is a high order page. > > With this change, Paweł hasn't noticed lock contention yet in > his workload and Jesper has noticed a 7% performance improvement > using a micro benchmark and lock contention is gone. I did the same tests on a 'low' speed 1Gbit interface on an cortex-a53. I used socionext's netsec driver and switched buffer allocation from the current scheme to using page_pool API (which by default allocates order0 pages). Running 'perf top' pre and post patch got me the same results. __free_pages_ok() disappeared from perf top and i got an ~11% performance boost testing with 64byte packets. Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org> Tested-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
On Mon, Nov 5, 2018 at 12:58 AM Aaron Lu <aaron.lu@intel.com> wrote: > > page_frag_free() calls __free_pages_ok() to free the page back to > Buddy. This is OK for high order page, but for order-0 pages, it > misses the optimization opportunity of using Per-Cpu-Pages and can > cause zone lock contention when called frequently. > > Paweł Staszewski recently shared his result of 'how Linux kernel > handles normal traffic'[1] and from perf data, Jesper Dangaard Brouer > found the lock contention comes from page allocator: > > mlx5e_poll_tx_cq > | > --16.34%--napi_consume_skb > | > |--12.65%--__free_pages_ok > | | > | --11.86%--free_one_page > | | > | |--10.10%--queued_spin_lock_slowpath > | | > | --0.65%--_raw_spin_lock > | > |--1.55%--page_frag_free > | > --1.44%--skb_release_data > > Jesper explained how it happened: mlx5 driver RX-page recycle > mechanism is not effective in this workload and pages have to go > through the page allocator. The lock contention happens during > mlx5 DMA TX completion cycle. And the page allocator cannot keep > up at these speeds.[2] > > I thought that __free_pages_ok() are mostly freeing high order > pages and thought this is an lock contention for high order pages > but Jesper explained in detail that __free_pages_ok() here are > actually freeing order-0 pages because mlx5 is using order-0 pages > to satisfy its page pool allocation request.[3] > > The free path as pointed out by Jesper is: > skb_free_head() > -> skb_free_frag() > -> skb_free_frag() > -> page_frag_free() > And the pages being freed on this path are order-0 pages. > > Fix this by doing similar things as in __page_frag_cache_drain() - > send the being freed page to PCP if it's an order-0 page, or > directly to Buddy if it is a high order page. > > With this change, Paweł hasn't noticed lock contention yet in > his workload and Jesper has noticed a 7% performance improvement > using a micro benchmark and lock contention is gone. > > [1]: https://www.spinics.net/lists/netdev/msg531362.html > [2]: https://www.spinics.net/lists/netdev/msg531421.html > [3]: https://www.spinics.net/lists/netdev/msg531556.html > Reported-by: Paweł Staszewski <pstaszewski@itcare.pl> > Analysed-by: Jesper Dangaard Brouer <brouer@redhat.com> > Signed-off-by: Aaron Lu <aaron.lu@intel.com> > --- > mm/page_alloc.c | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index ae31839874b8..91a9a6af41a2 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4555,8 +4555,14 @@ void page_frag_free(void *addr) > { > struct page *page = virt_to_head_page(addr); > > - if (unlikely(put_page_testzero(page))) > - __free_pages_ok(page, compound_order(page)); > + if (unlikely(put_page_testzero(page))) { > + unsigned int order = compound_order(page); > + > + if (order == 0) > + free_unref_page(page); > + else > + __free_pages_ok(page, order); > + } > } > EXPORT_SYMBOL(page_frag_free); > One thing I would suggest for Pawel to try would be to reduce the Tx qdisc size on his transmitting interfaces, Reduce the Tx ring size, and possibly increase the Tx interrupt rate. Ideally we shouldn't have too many packets in-flight and I suspect that is the issue that Pawel is seeing that is leading to the page pool allocator freeing up the memory. I know we like to try to batch things but the issue is processing too many Tx buffers in one batch leads to us eating up too much memory and causing evictions from the cache. Ideally the Rx and Tx rings and queues should be sized as small as possible while still allowing us to process up to our NAPI budget. Usually I run things with a 128 Rx / 128 Tx setup and then reduce the Tx queue length so we don't have more buffers stored there than we can place in the Tx ring. Then we can avoid the extra thrash of having to pull/push memory into and out of the freelists. Essentially the issue here ends up being another form of buffer bloat. With that said this change should be mostly harmless and does address the fact that we can have both regular order 0 pages and page frags used for skb->head. Acked-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
On 11/5/18 12:58 AM, Aaron Lu wrote: > - if (unlikely(put_page_testzero(page))) > - __free_pages_ok(page, compound_order(page)); > + if (unlikely(put_page_testzero(page))) { > + unsigned int order = compound_order(page); > + > + if (order == 0) > + free_unref_page(page); > + else > + __free_pages_ok(page, order); > + } > } This little hunk seems repeated in __free_pages() and __page_frag_cache_drain(). Do we need a common helper?
W dniu 05.11.2018 o 16:44, Alexander Duyck pisze: > On Mon, Nov 5, 2018 at 12:58 AM Aaron Lu <aaron.lu@intel.com> wrote: >> page_frag_free() calls __free_pages_ok() to free the page back to >> Buddy. This is OK for high order page, but for order-0 pages, it >> misses the optimization opportunity of using Per-Cpu-Pages and can >> cause zone lock contention when called frequently. >> >> Paweł Staszewski recently shared his result of 'how Linux kernel >> handles normal traffic'[1] and from perf data, Jesper Dangaard Brouer >> found the lock contention comes from page allocator: >> >> mlx5e_poll_tx_cq >> | >> --16.34%--napi_consume_skb >> | >> |--12.65%--__free_pages_ok >> | | >> | --11.86%--free_one_page >> | | >> | |--10.10%--queued_spin_lock_slowpath >> | | >> | --0.65%--_raw_spin_lock >> | >> |--1.55%--page_frag_free >> | >> --1.44%--skb_release_data >> >> Jesper explained how it happened: mlx5 driver RX-page recycle >> mechanism is not effective in this workload and pages have to go >> through the page allocator. The lock contention happens during >> mlx5 DMA TX completion cycle. And the page allocator cannot keep >> up at these speeds.[2] >> >> I thought that __free_pages_ok() are mostly freeing high order >> pages and thought this is an lock contention for high order pages >> but Jesper explained in detail that __free_pages_ok() here are >> actually freeing order-0 pages because mlx5 is using order-0 pages >> to satisfy its page pool allocation request.[3] >> >> The free path as pointed out by Jesper is: >> skb_free_head() >> -> skb_free_frag() >> -> skb_free_frag() >> -> page_frag_free() >> And the pages being freed on this path are order-0 pages. >> >> Fix this by doing similar things as in __page_frag_cache_drain() - >> send the being freed page to PCP if it's an order-0 page, or >> directly to Buddy if it is a high order page. >> >> With this change, Paweł hasn't noticed lock contention yet in >> his workload and Jesper has noticed a 7% performance improvement >> using a micro benchmark and lock contention is gone. >> >> [1]: https://www.spinics.net/lists/netdev/msg531362.html >> [2]: https://www.spinics.net/lists/netdev/msg531421.html >> [3]: https://www.spinics.net/lists/netdev/msg531556.html >> Reported-by: Paweł Staszewski <pstaszewski@itcare.pl> >> Analysed-by: Jesper Dangaard Brouer <brouer@redhat.com> >> Signed-off-by: Aaron Lu <aaron.lu@intel.com> >> --- >> mm/page_alloc.c | 10 ++++++++-- >> 1 file changed, 8 insertions(+), 2 deletions(-) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index ae31839874b8..91a9a6af41a2 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -4555,8 +4555,14 @@ void page_frag_free(void *addr) >> { >> struct page *page = virt_to_head_page(addr); >> >> - if (unlikely(put_page_testzero(page))) >> - __free_pages_ok(page, compound_order(page)); >> + if (unlikely(put_page_testzero(page))) { >> + unsigned int order = compound_order(page); >> + >> + if (order == 0) >> + free_unref_page(page); >> + else >> + __free_pages_ok(page, order); >> + } >> } >> EXPORT_SYMBOL(page_frag_free); >> > One thing I would suggest for Pawel to try would be to reduce the Tx > qdisc size on his transmitting interfaces, Reduce the Tx ring size, > and possibly increase the Tx interrupt rate. Ideally we shouldn't have > too many packets in-flight and I suspect that is the issue that Pawel > is seeing that is leading to the page pool allocator freeing up the > memory. I know we like to try to batch things but the issue is > processing too many Tx buffers in one batch leads to us eating up too > much memory and causing evictions from the cache. Ideally the Rx and > Tx rings and queues should be sized as small as possible while still > allowing us to process up to our NAPI budget. Usually I run things > with a 128 Rx / 128 Tx setup and then reduce the Tx queue length so we > don't have more buffers stored there than we can place in the Tx ring. > Then we can avoid the extra thrash of having to pull/push memory into > and out of the freelists. Essentially the issue here ends up being > another form of buffer bloat. Thanks Aleksandar - yes it can be - but in my scenario setting RX buffer <4096 producing more interface rx drops - and no_rx_buffer on network controller that is receiving more packets So i need to stick with 3000-4000 on RX - and yes i was trying to lower the TX buff on connectx4 - but that changed nothing before Aaron patch After Aaron patch - decreasing TX buffer influencing total bandwidth that can be handled by the router/server Dono why before this patch there was no difference there no matter what i set there there was always page_alloc/slowpath on top in perf Currently testing RX4096/TX256 - this helps with bandwidth like +10% more bandwidth with less interrupts... > > With that said this change should be mostly harmless and does address > the fact that we can have both regular order 0 pages and page frags > used for skb->head. > > Acked-by: Alexander Duyck <alexander.h.duyck@linux.intel.com> >
On Sat, Nov 10, 2018 at 3:54 PM Paweł Staszewski <pstaszewski@itcare.pl> wrote: > > > > W dniu 05.11.2018 o 16:44, Alexander Duyck pisze: > > On Mon, Nov 5, 2018 at 12:58 AM Aaron Lu <aaron.lu@intel.com> wrote: > >> page_frag_free() calls __free_pages_ok() to free the page back to > >> Buddy. This is OK for high order page, but for order-0 pages, it > >> misses the optimization opportunity of using Per-Cpu-Pages and can > >> cause zone lock contention when called frequently. > >> > >> Paweł Staszewski recently shared his result of 'how Linux kernel > >> handles normal traffic'[1] and from perf data, Jesper Dangaard Brouer > >> found the lock contention comes from page allocator: > >> > >> mlx5e_poll_tx_cq > >> | > >> --16.34%--napi_consume_skb > >> | > >> |--12.65%--__free_pages_ok > >> | | > >> | --11.86%--free_one_page > >> | | > >> | |--10.10%--queued_spin_lock_slowpath > >> | | > >> | --0.65%--_raw_spin_lock > >> | > >> |--1.55%--page_frag_free > >> | > >> --1.44%--skb_release_data > >> > >> Jesper explained how it happened: mlx5 driver RX-page recycle > >> mechanism is not effective in this workload and pages have to go > >> through the page allocator. The lock contention happens during > >> mlx5 DMA TX completion cycle. And the page allocator cannot keep > >> up at these speeds.[2] > >> > >> I thought that __free_pages_ok() are mostly freeing high order > >> pages and thought this is an lock contention for high order pages > >> but Jesper explained in detail that __free_pages_ok() here are > >> actually freeing order-0 pages because mlx5 is using order-0 pages > >> to satisfy its page pool allocation request.[3] > >> > >> The free path as pointed out by Jesper is: > >> skb_free_head() > >> -> skb_free_frag() > >> -> skb_free_frag() > >> -> page_frag_free() > >> And the pages being freed on this path are order-0 pages. > >> > >> Fix this by doing similar things as in __page_frag_cache_drain() - > >> send the being freed page to PCP if it's an order-0 page, or > >> directly to Buddy if it is a high order page. > >> > >> With this change, Paweł hasn't noticed lock contention yet in > >> his workload and Jesper has noticed a 7% performance improvement > >> using a micro benchmark and lock contention is gone. > >> > >> [1]: https://www.spinics.net/lists/netdev/msg531362.html > >> [2]: https://www.spinics.net/lists/netdev/msg531421.html > >> [3]: https://www.spinics.net/lists/netdev/msg531556.html > >> Reported-by: Paweł Staszewski <pstaszewski@itcare.pl> > >> Analysed-by: Jesper Dangaard Brouer <brouer@redhat.com> > >> Signed-off-by: Aaron Lu <aaron.lu@intel.com> > >> --- > >> mm/page_alloc.c | 10 ++++++++-- > >> 1 file changed, 8 insertions(+), 2 deletions(-) > >> > >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c > >> index ae31839874b8..91a9a6af41a2 100644 > >> --- a/mm/page_alloc.c > >> +++ b/mm/page_alloc.c > >> @@ -4555,8 +4555,14 @@ void page_frag_free(void *addr) > >> { > >> struct page *page = virt_to_head_page(addr); > >> > >> - if (unlikely(put_page_testzero(page))) > >> - __free_pages_ok(page, compound_order(page)); > >> + if (unlikely(put_page_testzero(page))) { > >> + unsigned int order = compound_order(page); > >> + > >> + if (order == 0) > >> + free_unref_page(page); > >> + else > >> + __free_pages_ok(page, order); > >> + } > >> } > >> EXPORT_SYMBOL(page_frag_free); > >> > > One thing I would suggest for Pawel to try would be to reduce the Tx > > qdisc size on his transmitting interfaces, Reduce the Tx ring size, > > and possibly increase the Tx interrupt rate. Ideally we shouldn't have > > too many packets in-flight and I suspect that is the issue that Pawel > > is seeing that is leading to the page pool allocator freeing up the > > memory. I know we like to try to batch things but the issue is > > processing too many Tx buffers in one batch leads to us eating up too > > much memory and causing evictions from the cache. Ideally the Rx and > > Tx rings and queues should be sized as small as possible while still > > allowing us to process up to our NAPI budget. Usually I run things > > with a 128 Rx / 128 Tx setup and then reduce the Tx queue length so we > > don't have more buffers stored there than we can place in the Tx ring. > > Then we can avoid the extra thrash of having to pull/push memory into > > and out of the freelists. Essentially the issue here ends up being > > another form of buffer bloat. > Thanks Aleksandar - yes it can be - but in my scenario setting RX buffer > <4096 producing more interface rx drops - and no_rx_buffer on network > controller that is receiving more packets > So i need to stick with 3000-4000 on RX - and yes i was trying to lower > the TX buff on connectx4 - but that changed nothing before Aaron patch > > After Aaron patch - decreasing TX buffer influencing total bandwidth > that can be handled by the router/server > Dono why before this patch there was no difference there no matter what > i set there there was always page_alloc/slowpath on top in perf > > > Currently testing RX4096/TX256 - this helps with bandwidth like +10% > more bandwidth with less interrupts... The problem is if you are going for less interrupts you are setting yourself up for buffer bloat. Basically you are going to use much more cache and much more memory then you actually need and if things are properly configured NAPI should take care of the interrupts anyway since under maximum load you shouldn't stop polling normally. One issue I have seen is people delay interrupts for as long as possible which isn't really a good thing since most network controllers will use NAPI which will disable the interrupts and leave them disabled whenever the system is under heavy stress so you should be able to get the maximum performance by configuring an adapter with small ring sizes and for high interrupt rates. It is easiest to think of it this way. Your total packet rate is equal to your interrupt rate times the number of buffers you will store in the ring. So if you have some fixed rate "X" for packets and an interrupt rate of "i" then your optimal ring size should be "X/i". So if you lower the interrupt rate you end up hurting the throughput unless you increase the buffer size. However at a certain point the buffer size starts becoming an issue. For example with UDP flows I often see massive packet drops if you tune the interrupt rate too low and then put the system under heavy stress. - Alex
W dniu 12.11.2018 o 00:05, Alexander Duyck pisze: > On Sat, Nov 10, 2018 at 3:54 PM Paweł Staszewski <pstaszewski@itcare.pl> wrote: >> >> >> W dniu 05.11.2018 o 16:44, Alexander Duyck pisze: >>> On Mon, Nov 5, 2018 at 12:58 AM Aaron Lu <aaron.lu@intel.com> wrote: >>>> page_frag_free() calls __free_pages_ok() to free the page back to >>>> Buddy. This is OK for high order page, but for order-0 pages, it >>>> misses the optimization opportunity of using Per-Cpu-Pages and can >>>> cause zone lock contention when called frequently. >>>> >>>> Paweł Staszewski recently shared his result of 'how Linux kernel >>>> handles normal traffic'[1] and from perf data, Jesper Dangaard Brouer >>>> found the lock contention comes from page allocator: >>>> >>>> mlx5e_poll_tx_cq >>>> | >>>> --16.34%--napi_consume_skb >>>> | >>>> |--12.65%--__free_pages_ok >>>> | | >>>> | --11.86%--free_one_page >>>> | | >>>> | |--10.10%--queued_spin_lock_slowpath >>>> | | >>>> | --0.65%--_raw_spin_lock >>>> | >>>> |--1.55%--page_frag_free >>>> | >>>> --1.44%--skb_release_data >>>> >>>> Jesper explained how it happened: mlx5 driver RX-page recycle >>>> mechanism is not effective in this workload and pages have to go >>>> through the page allocator. The lock contention happens during >>>> mlx5 DMA TX completion cycle. And the page allocator cannot keep >>>> up at these speeds.[2] >>>> >>>> I thought that __free_pages_ok() are mostly freeing high order >>>> pages and thought this is an lock contention for high order pages >>>> but Jesper explained in detail that __free_pages_ok() here are >>>> actually freeing order-0 pages because mlx5 is using order-0 pages >>>> to satisfy its page pool allocation request.[3] >>>> >>>> The free path as pointed out by Jesper is: >>>> skb_free_head() >>>> -> skb_free_frag() >>>> -> skb_free_frag() >>>> -> page_frag_free() >>>> And the pages being freed on this path are order-0 pages. >>>> >>>> Fix this by doing similar things as in __page_frag_cache_drain() - >>>> send the being freed page to PCP if it's an order-0 page, or >>>> directly to Buddy if it is a high order page. >>>> >>>> With this change, Paweł hasn't noticed lock contention yet in >>>> his workload and Jesper has noticed a 7% performance improvement >>>> using a micro benchmark and lock contention is gone. >>>> >>>> [1]: https://www.spinics.net/lists/netdev/msg531362.html >>>> [2]: https://www.spinics.net/lists/netdev/msg531421.html >>>> [3]: https://www.spinics.net/lists/netdev/msg531556.html >>>> Reported-by: Paweł Staszewski <pstaszewski@itcare.pl> >>>> Analysed-by: Jesper Dangaard Brouer <brouer@redhat.com> >>>> Signed-off-by: Aaron Lu <aaron.lu@intel.com> >>>> --- >>>> mm/page_alloc.c | 10 ++++++++-- >>>> 1 file changed, 8 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>>> index ae31839874b8..91a9a6af41a2 100644 >>>> --- a/mm/page_alloc.c >>>> +++ b/mm/page_alloc.c >>>> @@ -4555,8 +4555,14 @@ void page_frag_free(void *addr) >>>> { >>>> struct page *page = virt_to_head_page(addr); >>>> >>>> - if (unlikely(put_page_testzero(page))) >>>> - __free_pages_ok(page, compound_order(page)); >>>> + if (unlikely(put_page_testzero(page))) { >>>> + unsigned int order = compound_order(page); >>>> + >>>> + if (order == 0) >>>> + free_unref_page(page); >>>> + else >>>> + __free_pages_ok(page, order); >>>> + } >>>> } >>>> EXPORT_SYMBOL(page_frag_free); >>>> >>> One thing I would suggest for Pawel to try would be to reduce the Tx >>> qdisc size on his transmitting interfaces, Reduce the Tx ring size, >>> and possibly increase the Tx interrupt rate. Ideally we shouldn't have >>> too many packets in-flight and I suspect that is the issue that Pawel >>> is seeing that is leading to the page pool allocator freeing up the >>> memory. I know we like to try to batch things but the issue is >>> processing too many Tx buffers in one batch leads to us eating up too >>> much memory and causing evictions from the cache. Ideally the Rx and >>> Tx rings and queues should be sized as small as possible while still >>> allowing us to process up to our NAPI budget. Usually I run things >>> with a 128 Rx / 128 Tx setup and then reduce the Tx queue length so we >>> don't have more buffers stored there than we can place in the Tx ring. >>> Then we can avoid the extra thrash of having to pull/push memory into >>> and out of the freelists. Essentially the issue here ends up being >>> another form of buffer bloat. >> Thanks Aleksandar - yes it can be - but in my scenario setting RX buffer >> <4096 producing more interface rx drops - and no_rx_buffer on network >> controller that is receiving more packets >> So i need to stick with 3000-4000 on RX - and yes i was trying to lower >> the TX buff on connectx4 - but that changed nothing before Aaron patch >> >> After Aaron patch - decreasing TX buffer influencing total bandwidth >> that can be handled by the router/server >> Dono why before this patch there was no difference there no matter what >> i set there there was always page_alloc/slowpath on top in perf >> >> >> Currently testing RX4096/TX256 - this helps with bandwidth like +10% >> more bandwidth with less interrupts... > The problem is if you are going for less interrupts you are setting > yourself up for buffer bloat. Basically you are going to use much more > cache and much more memory then you actually need and if things are > properly configured NAPI should take care of the interrupts anyway > since under maximum load you shouldn't stop polling normally. Im trying to balance here - there is problem cause server is forwarding all kingd of protocols packets/different size etc The problem is im trying to go in high interrupt rate - but Setting coalescence to adaptative for rx killing cpu's at 22Gbit/s RX and 22Gbit with rly high interrupt rate So adding a little more latency i can turn off adaptative rx and setup rx-usecs from range 16-64 - and this gives me more or less interrupts - but the problem is - always same bandwidth as maximum > > One issue I have seen is people delay interrupts for as long as > possible which isn't really a good thing since most network > controllers will use NAPI which will disable the interrupts and leave > them disabled whenever the system is under heavy stress so you should > be able to get the maximum performance by configuring an adapter with > small ring sizes and for high interrupt rates. Sure this is bad to setup rx-usec for high values - cause at some point this will add high latency for packet traversing both sides - and start to hurt buffers But my problem is a little different now i have no problems with RX side - cause i can setup anything like: coalescence from 16 to 64 rx ring from 3000 to max 8192 And it does not change my max bw - only produces less or more interrupts. So I start to change params for TX side - and for now i know that the best for me is coalescence adaptative on TX buffer 128 This helps with max BW that for now is close to 70Gbit/s RX and 70Gbit TX but after this change i have increasing DROPS on TX side for vlan interfaces. And only 50% cpu (max was 50% for 70Gbit/s) > It is easiest to think of it this way. Your total packet rate is equal > to your interrupt rate times the number of buffers you will store in > the ring. So if you have some fixed rate "X" for packets and an > interrupt rate of "i" then your optimal ring size should be "X/i". So > if you lower the interrupt rate you end up hurting the throughput > unless you increase the buffer size. However at a certain point the > buffer size starts becoming an issue. For example with UDP flows I > often see massive packet drops if you tune the interrupt rate too low > and then put the system under heavy stress. Yes - in normal life traffic - most of ddos'es are like this many pps with small frames. > - Alex >
On Sun, Nov 11, 2018 at 4:39 PM Paweł Staszewski <pstaszewski@itcare.pl> wrote: > > > W dniu 12.11.2018 o 00:05, Alexander Duyck pisze: > > On Sat, Nov 10, 2018 at 3:54 PM Paweł Staszewski <pstaszewski@itcare.pl> wrote: > >> > >> > >> W dniu 05.11.2018 o 16:44, Alexander Duyck pisze: > >>> On Mon, Nov 5, 2018 at 12:58 AM Aaron Lu <aaron.lu@intel.com> wrote: > >>>> page_frag_free() calls __free_pages_ok() to free the page back to > >>>> Buddy. This is OK for high order page, but for order-0 pages, it > >>>> misses the optimization opportunity of using Per-Cpu-Pages and can > >>>> cause zone lock contention when called frequently. > >>>> > >>>> Paweł Staszewski recently shared his result of 'how Linux kernel > >>>> handles normal traffic'[1] and from perf data, Jesper Dangaard Brouer > >>>> found the lock contention comes from page allocator: > >>>> > >>>> mlx5e_poll_tx_cq > >>>> | > >>>> --16.34%--napi_consume_skb > >>>> | > >>>> |--12.65%--__free_pages_ok > >>>> | | > >>>> | --11.86%--free_one_page > >>>> | | > >>>> | |--10.10%--queued_spin_lock_slowpath > >>>> | | > >>>> | --0.65%--_raw_spin_lock > >>>> | > >>>> |--1.55%--page_frag_free > >>>> | > >>>> --1.44%--skb_release_data > >>>> > >>>> Jesper explained how it happened: mlx5 driver RX-page recycle > >>>> mechanism is not effective in this workload and pages have to go > >>>> through the page allocator. The lock contention happens during > >>>> mlx5 DMA TX completion cycle. And the page allocator cannot keep > >>>> up at these speeds.[2] > >>>> > >>>> I thought that __free_pages_ok() are mostly freeing high order > >>>> pages and thought this is an lock contention for high order pages > >>>> but Jesper explained in detail that __free_pages_ok() here are > >>>> actually freeing order-0 pages because mlx5 is using order-0 pages > >>>> to satisfy its page pool allocation request.[3] > >>>> > >>>> The free path as pointed out by Jesper is: > >>>> skb_free_head() > >>>> -> skb_free_frag() > >>>> -> skb_free_frag() > >>>> -> page_frag_free() > >>>> And the pages being freed on this path are order-0 pages. > >>>> > >>>> Fix this by doing similar things as in __page_frag_cache_drain() - > >>>> send the being freed page to PCP if it's an order-0 page, or > >>>> directly to Buddy if it is a high order page. > >>>> > >>>> With this change, Paweł hasn't noticed lock contention yet in > >>>> his workload and Jesper has noticed a 7% performance improvement > >>>> using a micro benchmark and lock contention is gone. > >>>> > >>>> [1]: https://www.spinics.net/lists/netdev/msg531362.html > >>>> [2]: https://www.spinics.net/lists/netdev/msg531421.html > >>>> [3]: https://www.spinics.net/lists/netdev/msg531556.html > >>>> Reported-by: Paweł Staszewski <pstaszewski@itcare.pl> > >>>> Analysed-by: Jesper Dangaard Brouer <brouer@redhat.com> > >>>> Signed-off-by: Aaron Lu <aaron.lu@intel.com> > >>>> --- > >>>> mm/page_alloc.c | 10 ++++++++-- > >>>> 1 file changed, 8 insertions(+), 2 deletions(-) > >>>> > >>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c > >>>> index ae31839874b8..91a9a6af41a2 100644 > >>>> --- a/mm/page_alloc.c > >>>> +++ b/mm/page_alloc.c > >>>> @@ -4555,8 +4555,14 @@ void page_frag_free(void *addr) > >>>> { > >>>> struct page *page = virt_to_head_page(addr); > >>>> > >>>> - if (unlikely(put_page_testzero(page))) > >>>> - __free_pages_ok(page, compound_order(page)); > >>>> + if (unlikely(put_page_testzero(page))) { > >>>> + unsigned int order = compound_order(page); > >>>> + > >>>> + if (order == 0) > >>>> + free_unref_page(page); > >>>> + else > >>>> + __free_pages_ok(page, order); > >>>> + } > >>>> } > >>>> EXPORT_SYMBOL(page_frag_free); > >>>> > >>> One thing I would suggest for Pawel to try would be to reduce the Tx > >>> qdisc size on his transmitting interfaces, Reduce the Tx ring size, > >>> and possibly increase the Tx interrupt rate. Ideally we shouldn't have > >>> too many packets in-flight and I suspect that is the issue that Pawel > >>> is seeing that is leading to the page pool allocator freeing up the > >>> memory. I know we like to try to batch things but the issue is > >>> processing too many Tx buffers in one batch leads to us eating up too > >>> much memory and causing evictions from the cache. Ideally the Rx and > >>> Tx rings and queues should be sized as small as possible while still > >>> allowing us to process up to our NAPI budget. Usually I run things > >>> with a 128 Rx / 128 Tx setup and then reduce the Tx queue length so we > >>> don't have more buffers stored there than we can place in the Tx ring. > >>> Then we can avoid the extra thrash of having to pull/push memory into > >>> and out of the freelists. Essentially the issue here ends up being > >>> another form of buffer bloat. > >> Thanks Aleksandar - yes it can be - but in my scenario setting RX buffer > >> <4096 producing more interface rx drops - and no_rx_buffer on network > >> controller that is receiving more packets > >> So i need to stick with 3000-4000 on RX - and yes i was trying to lower > >> the TX buff on connectx4 - but that changed nothing before Aaron patch > >> > >> After Aaron patch - decreasing TX buffer influencing total bandwidth > >> that can be handled by the router/server > >> Dono why before this patch there was no difference there no matter what > >> i set there there was always page_alloc/slowpath on top in perf > >> > >> > >> Currently testing RX4096/TX256 - this helps with bandwidth like +10% > >> more bandwidth with less interrupts... > > The problem is if you are going for less interrupts you are setting > > yourself up for buffer bloat. Basically you are going to use much more > > cache and much more memory then you actually need and if things are > > properly configured NAPI should take care of the interrupts anyway > > since under maximum load you shouldn't stop polling normally. > > Im trying to balance here - there is problem cause server is forwarding > all kingd of protocols packets/different size etc > > The problem is im trying to go in high interrupt rate - but > > Setting coalescence to adaptative for rx killing cpu's at 22Gbit/s RX > and 22Gbit with rly high interrupt rate I wouldn't recommend adaptive just because the behavior would be hard to predict. > So adding a little more latency i can turn off adaptative rx and setup > rx-usecs from range 16-64 - and this gives me more or less interrupts - > but the problem is - always same bandwidth as maximum What about the tx-usecs, is that a functional thing for the adapter you are using? The Rx side logic should be pretty easy to figure out. Essentially you want to keep the Rx ring size as small as possible while at the same time avoiding storming the system with interrupts. I know for 10Gb/s I have used a value of 25us in the past. What you want to watch for is if you are dropping packets on the Rx side or not. Ideally you want enough buffers that you can capture any burst while you wait for the interrupt routine to catch up. > > > > One issue I have seen is people delay interrupts for as long as > > possible which isn't really a good thing since most network > > controllers will use NAPI which will disable the interrupts and leave > > them disabled whenever the system is under heavy stress so you should > > be able to get the maximum performance by configuring an adapter with > > small ring sizes and for high interrupt rates. > > Sure this is bad to setup rx-usec for high values - cause at some point > this will add high latency for packet traversing both sides - and start > to hurt buffers > > But my problem is a little different now i have no problems with RX side > - cause i can setup anything like: > > coalescence from 16 to 64 > > rx ring from 3000 to max 8192 > > And it does not change my max bw - only produces less or more interrupts. Right so the issue itself isn't Rx, you aren't throttled there. We are probably looking at an issue of PCIe bandwidth or Tx slowing things down. The fact that you are still filing interrupts is a bit surprising though. Are the Tx and Rx interrupts linked for the device you are using or are they firing them seperately? Normally Rx traffic won't generate many interrupts under a stress test as NAPI will leave the interrupts disabled unless it can keep up. Anyway, my suggestion would be to look at tuning things for as small a ring size as possible. > So I start to change params for TX side - and for now i know that the > best for me is > > coalescence adaptative on > > TX buffer 128 > > This helps with max BW that for now is close to 70Gbit/s RX and 70Gbit > TX but after this change i have increasing DROPS on TX side for vlan > interfaces. So this sounds like you are likely bottlenecked due to either PCIe bandwidth or latency. When you start putting back-pressure on the Tx like you have described it starts pushing packets onto the Qdisc layer. One thing that happens when packets are on the qdisc layer is that they can start to perform a bulk dequeue. The side effect of this is that you write multiple packets to the descriptor ring and then update the hardware doorbell only once for the entire group of packets instead of once per packet. > And only 50% cpu (max was 50% for 70Gbit/s) > > > > It is easiest to think of it this way. Your total packet rate is equal > > to your interrupt rate times the number of buffers you will store in > > the ring. So if you have some fixed rate "X" for packets and an > > interrupt rate of "i" then your optimal ring size should be "X/i". So > > if you lower the interrupt rate you end up hurting the throughput > > unless you increase the buffer size. However at a certain point the > > buffer size starts becoming an issue. For example with UDP flows I > > often see massive packet drops if you tune the interrupt rate too low > > and then put the system under heavy stress. > > Yes - in normal life traffic - most of ddos'es are like this many pps > with small frames. It sounds to me like XDP would probably be your best bet. With that you could probably get away with smaller ring sizes, higher interrupt rates, and get the advantage of it batching the Tx without having to drop packets.
On 11/12/2018 07:30 AM, Alexander Duyck wrote: > It sounds to me like XDP would probably be your best bet. With that > you could probably get away with smaller ring sizes, higher interrupt > rates, and get the advantage of it batching the Tx without having to > drop packets. Add to this that with XDP (or anything lowering per packet processing costs) you can reduce number of cpus/queues, get better latencies, and bigger TX batches.
W dniu 12.11.2018 o 16:30, Alexander Duyck pisze: > On Sun, Nov 11, 2018 at 4:39 PM Paweł Staszewski <pstaszewski@itcare.pl> wrote: >> >> W dniu 12.11.2018 o 00:05, Alexander Duyck pisze: >>> On Sat, Nov 10, 2018 at 3:54 PM Paweł Staszewski <pstaszewski@itcare.pl> wrote: >>>> >>>> W dniu 05.11.2018 o 16:44, Alexander Duyck pisze: >>>>> On Mon, Nov 5, 2018 at 12:58 AM Aaron Lu <aaron.lu@intel.com> wrote: >>>>>> page_frag_free() calls __free_pages_ok() to free the page back to >>>>>> Buddy. This is OK for high order page, but for order-0 pages, it >>>>>> misses the optimization opportunity of using Per-Cpu-Pages and can >>>>>> cause zone lock contention when called frequently. >>>>>> >>>>>> Paweł Staszewski recently shared his result of 'how Linux kernel >>>>>> handles normal traffic'[1] and from perf data, Jesper Dangaard Brouer >>>>>> found the lock contention comes from page allocator: >>>>>> >>>>>> mlx5e_poll_tx_cq >>>>>> | >>>>>> --16.34%--napi_consume_skb >>>>>> | >>>>>> |--12.65%--__free_pages_ok >>>>>> | | >>>>>> | --11.86%--free_one_page >>>>>> | | >>>>>> | |--10.10%--queued_spin_lock_slowpath >>>>>> | | >>>>>> | --0.65%--_raw_spin_lock >>>>>> | >>>>>> |--1.55%--page_frag_free >>>>>> | >>>>>> --1.44%--skb_release_data >>>>>> >>>>>> Jesper explained how it happened: mlx5 driver RX-page recycle >>>>>> mechanism is not effective in this workload and pages have to go >>>>>> through the page allocator. The lock contention happens during >>>>>> mlx5 DMA TX completion cycle. And the page allocator cannot keep >>>>>> up at these speeds.[2] >>>>>> >>>>>> I thought that __free_pages_ok() are mostly freeing high order >>>>>> pages and thought this is an lock contention for high order pages >>>>>> but Jesper explained in detail that __free_pages_ok() here are >>>>>> actually freeing order-0 pages because mlx5 is using order-0 pages >>>>>> to satisfy its page pool allocation request.[3] >>>>>> >>>>>> The free path as pointed out by Jesper is: >>>>>> skb_free_head() >>>>>> -> skb_free_frag() >>>>>> -> skb_free_frag() >>>>>> -> page_frag_free() >>>>>> And the pages being freed on this path are order-0 pages. >>>>>> >>>>>> Fix this by doing similar things as in __page_frag_cache_drain() - >>>>>> send the being freed page to PCP if it's an order-0 page, or >>>>>> directly to Buddy if it is a high order page. >>>>>> >>>>>> With this change, Paweł hasn't noticed lock contention yet in >>>>>> his workload and Jesper has noticed a 7% performance improvement >>>>>> using a micro benchmark and lock contention is gone. >>>>>> >>>>>> [1]: https://www.spinics.net/lists/netdev/msg531362.html >>>>>> [2]: https://www.spinics.net/lists/netdev/msg531421.html >>>>>> [3]: https://www.spinics.net/lists/netdev/msg531556.html >>>>>> Reported-by: Paweł Staszewski <pstaszewski@itcare.pl> >>>>>> Analysed-by: Jesper Dangaard Brouer <brouer@redhat.com> >>>>>> Signed-off-by: Aaron Lu <aaron.lu@intel.com> >>>>>> --- >>>>>> mm/page_alloc.c | 10 ++++++++-- >>>>>> 1 file changed, 8 insertions(+), 2 deletions(-) >>>>>> >>>>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>>>>> index ae31839874b8..91a9a6af41a2 100644 >>>>>> --- a/mm/page_alloc.c >>>>>> +++ b/mm/page_alloc.c >>>>>> @@ -4555,8 +4555,14 @@ void page_frag_free(void *addr) >>>>>> { >>>>>> struct page *page = virt_to_head_page(addr); >>>>>> >>>>>> - if (unlikely(put_page_testzero(page))) >>>>>> - __free_pages_ok(page, compound_order(page)); >>>>>> + if (unlikely(put_page_testzero(page))) { >>>>>> + unsigned int order = compound_order(page); >>>>>> + >>>>>> + if (order == 0) >>>>>> + free_unref_page(page); >>>>>> + else >>>>>> + __free_pages_ok(page, order); >>>>>> + } >>>>>> } >>>>>> EXPORT_SYMBOL(page_frag_free); >>>>>> >>>>> One thing I would suggest for Pawel to try would be to reduce the Tx >>>>> qdisc size on his transmitting interfaces, Reduce the Tx ring size, >>>>> and possibly increase the Tx interrupt rate. Ideally we shouldn't have >>>>> too many packets in-flight and I suspect that is the issue that Pawel >>>>> is seeing that is leading to the page pool allocator freeing up the >>>>> memory. I know we like to try to batch things but the issue is >>>>> processing too many Tx buffers in one batch leads to us eating up too >>>>> much memory and causing evictions from the cache. Ideally the Rx and >>>>> Tx rings and queues should be sized as small as possible while still >>>>> allowing us to process up to our NAPI budget. Usually I run things >>>>> with a 128 Rx / 128 Tx setup and then reduce the Tx queue length so we >>>>> don't have more buffers stored there than we can place in the Tx ring. >>>>> Then we can avoid the extra thrash of having to pull/push memory into >>>>> and out of the freelists. Essentially the issue here ends up being >>>>> another form of buffer bloat. >>>> Thanks Aleksandar - yes it can be - but in my scenario setting RX buffer >>>> <4096 producing more interface rx drops - and no_rx_buffer on network >>>> controller that is receiving more packets >>>> So i need to stick with 3000-4000 on RX - and yes i was trying to lower >>>> the TX buff on connectx4 - but that changed nothing before Aaron patch >>>> >>>> After Aaron patch - decreasing TX buffer influencing total bandwidth >>>> that can be handled by the router/server >>>> Dono why before this patch there was no difference there no matter what >>>> i set there there was always page_alloc/slowpath on top in perf >>>> >>>> >>>> Currently testing RX4096/TX256 - this helps with bandwidth like +10% >>>> more bandwidth with less interrupts... >>> The problem is if you are going for less interrupts you are setting >>> yourself up for buffer bloat. Basically you are going to use much more >>> cache and much more memory then you actually need and if things are >>> properly configured NAPI should take care of the interrupts anyway >>> since under maximum load you shouldn't stop polling normally. >> Im trying to balance here - there is problem cause server is forwarding >> all kingd of protocols packets/different size etc >> >> The problem is im trying to go in high interrupt rate - but >> >> Setting coalescence to adaptative for rx killing cpu's at 22Gbit/s RX >> and 22Gbit with rly high interrupt rate > I wouldn't recommend adaptive just because the behavior would be hard > to predict. > >> So adding a little more latency i can turn off adaptative rx and setup >> rx-usecs from range 16-64 - and this gives me more or less interrupts - >> but the problem is - always same bandwidth as maximum > What about the tx-usecs, is that a functional thing for the adapter > you are using? Yes tx-usecs is not used now cause of adaptative mode on tx side: ethtool -c enp175s0 Coalesce parameters for enp175s0: Adaptive RX: off TX: on stats-block-usecs: 0 sample-interval: 0 pkt-rate-low: 0 pkt-rate-high: 0 dmac: 32551 rx-usecs: 64 rx-frames: 128 rx-usecs-irq: 0 rx-frames-irq: 0 tx-usecs: 8 tx-frames: 64 tx-usecs-irq: 0 tx-frames-irq: 0 rx-usecs-low: 0 rx-frame-low: 0 tx-usecs-low: 0 tx-frame-low: 0 rx-usecs-high: 0 rx-frame-high: 0 tx-usecs-high: 0 tx-frame-high: 0 > > The Rx side logic should be pretty easy to figure out. Essentially you > want to keep the Rx ring size as small as possible while at the same > time avoiding storming the system with interrupts. I know for 10Gb/s I > have used a value of 25us in the past. What you want to watch for is > if you are dropping packets on the Rx side or not. Ideally you want > enough buffers that you can capture any burst while you wait for the > interrupt routine to catch up. > >>> One issue I have seen is people delay interrupts for as long as >>> possible which isn't really a good thing since most network >>> controllers will use NAPI which will disable the interrupts and leave >>> them disabled whenever the system is under heavy stress so you should >>> be able to get the maximum performance by configuring an adapter with >>> small ring sizes and for high interrupt rates. >> Sure this is bad to setup rx-usec for high values - cause at some point >> this will add high latency for packet traversing both sides - and start >> to hurt buffers >> >> But my problem is a little different now i have no problems with RX side >> - cause i can setup anything like: >> >> coalescence from 16 to 64 >> >> rx ring from 3000 to max 8192 >> >> And it does not change my max bw - only produces less or more interrupts. > Right so the issue itself isn't Rx, you aren't throttled there. We are > probably looking at an issue of PCIe bandwidth or Tx slowing things > down. The fact that you are still filing interrupts is a bit > surprising though. Are the Tx and Rx interrupts linked for the device > you are using or are they firing them seperately? Normally Rx traffic > won't generate many interrupts under a stress test as NAPI will leave > the interrupts disabled unless it can keep up. Anyway, my suggestion > would be to look at tuning things for as small a ring size as > possible. PCIe bw was eliminated - previously there was one 2 port 100G card installed in one pciex16 (max bw for pcie x16 gen3 is 32GB/s 16/16GB bidirectional) Currently there are two separate nic's installed in two separate x16 slots - so can't be problem with pcie bandwidth But i think I reach memory bandwidth limit now for 70Gbit/70Gbit :) But wondering if there is any counter that can help me to diagnose problems with memory bandwidth ? stream app tests gives me results like: ./stream_c.exe ------------------------------------------------------------- STREAM version $Revision: 5.10 $ ------------------------------------------------------------- This system uses 8 bytes per array element. ------------------------------------------------------------- Array size = 10000000 (elements), Offset = 0 (elements) Memory per array = 76.3 MiB (= 0.1 GiB). Total memory required = 228.9 MiB (= 0.2 GiB). Each kernel will be executed 10 times. The *best* time for each kernel (excluding the first iteration) will be used to compute the reported bandwidth. ------------------------------------------------------------- Number of Threads requested = 56 Number of Threads counted = 56 ------------------------------------------------------------- Your clock granularity/precision appears to be 1 microseconds. Each test below will take on the order of 4081 microseconds. (= 4081 clock ticks) Increase the size of the arrays if this shows that you are not getting at least 20 clock ticks per test. ------------------------------------------------------------- WARNING -- The above is only a rough guideline. For best results, please be sure you know the precision of your system timer. ------------------------------------------------------------- Function Best Rate MB/s Avg time Min time Max time Copy: 29907.2 0.005382 0.005350 0.005405 Scale: 28787.3 0.005611 0.005558 0.005650 Add: 34153.3 0.007037 0.007027 0.007055 Triad: 34944.0 0.006880 0.006868 0.006887 ------------------------------------------------------------- Solution Validates: avg error less than 1.000000e-13 on all three arrays But this is for node 0+1 When limiting test to one node and cores used by network controllers: ------------------------------------------------------------- STREAM version $Revision: 5.10 $ ------------------------------------------------------------- This system uses 8 bytes per array element. ------------------------------------------------------------- Array size = 10000000 (elements), Offset = 0 (elements) Memory per array = 76.3 MiB (= 0.1 GiB). Total memory required = 228.9 MiB (= 0.2 GiB). Each kernel will be executed 10 times. The *best* time for each kernel (excluding the first iteration) will be used to compute the reported bandwidth. ------------------------------------------------------------- Number of Threads requested = 28 Number of Threads counted = 28 ------------------------------------------------------------- Your clock granularity/precision appears to be 1 microseconds. Each test below will take on the order of 6107 microseconds. (= 6107 clock ticks) Increase the size of the arrays if this shows that you are not getting at least 20 clock ticks per test. ------------------------------------------------------------- WARNING -- The above is only a rough guideline. For best results, please be sure you know the precision of your system timer. ------------------------------------------------------------- Function Best Rate MB/s Avg time Min time Max time Copy: 20156.4 0.007946 0.007938 0.007958 Scale: 19436.1 0.008237 0.008232 0.008243 Add: 20184.7 0.011896 0.011890 0.011904 Triad: 20687.9 0.011607 0.011601 0.011613 ------------------------------------------------------------- Solution Validates: avg error less than 1.000000e-13 on all three arrays ------------------------------------------------------------- Close to the limit but still some place - there can be some doubled operations like for RX/TX side and network controllers can use more bandwidth or just can't do this more optimally - cause of bulking/buffers etc. So currently there are only four from six channels used - i will upgrade also memory and populate all six channels left/right side for two memory controllers that cpu have. >> So I start to change params for TX side - and for now i know that the >> best for me is >> >> coalescence adaptative on >> >> TX buffer 128 >> >> This helps with max BW that for now is close to 70Gbit/s RX and 70Gbit >> TX but after this change i have increasing DROPS on TX side for vlan >> interfaces. > So this sounds like you are likely bottlenecked due to either PCIe > bandwidth or latency. When you start putting back-pressure on the Tx > like you have described it starts pushing packets onto the Qdisc > layer. One thing that happens when packets are on the qdisc layer is > that they can start to perform a bulk dequeue. The side effect of this > is that you write multiple packets to the descriptor ring and then > update the hardware doorbell only once for the entire group of packets > instead of once per packet. yes the problem is i just can't find any place where counters will shows me why nic's start to drop packets it does not reflect in cpu load or any other counter besides rx_phy drops and tx_vlan drop packets >> And only 50% cpu (max was 50% for 70Gbit/s) >> >> >>> It is easiest to think of it this way. Your total packet rate is equal >>> to your interrupt rate times the number of buffers you will store in >>> the ring. So if you have some fixed rate "X" for packets and an >>> interrupt rate of "i" then your optimal ring size should be "X/i". So >>> if you lower the interrupt rate you end up hurting the throughput >>> unless you increase the buffer size. However at a certain point the >>> buffer size starts becoming an issue. For example with UDP flows I >>> often see massive packet drops if you tune the interrupt rate too low >>> and then put the system under heavy stress. >> Yes - in normal life traffic - most of ddos'es are like this many pps >> with small frames. > It sounds to me like XDP would probably be your best bet. With that > you could probably get away with smaller ring sizes, higher interrupt > rates, and get the advantage of it batching the Tx without having to > drop packets. Yes im testing in lab xdp_fwd currently - but have some problems with random drops that occuring randomly where server forwards only 1/10 packet and after some time it starts to work normally. Currently trying to eliminate nic's offloading that can cause this - so turning off one by one and running tests.
W dniu 12.11.2018 o 16:44, Eric Dumazet pisze: > > On 11/12/2018 07:30 AM, Alexander Duyck wrote: > >> It sounds to me like XDP would probably be your best bet. With that >> you could probably get away with smaller ring sizes, higher interrupt >> rates, and get the advantage of it batching the Tx without having to >> drop packets. > Add to this that with XDP (or anything lowering per packet processing costs) > you can reduce number of cpus/queues, get better latencies, and bigger TX batches. Yes for sure - the best for my use case will be to implement XDP :) But for real life not test lab use programs like xdp_fwd need to be extended for minimal information needed from IP router - like counters and some aditional debug for traffic like sniffing / sampling for ddos detection. And that is rly minimum needed - for routing IP traffic with XDP
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index ae31839874b8..91a9a6af41a2 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -4555,8 +4555,14 @@ void page_frag_free(void *addr) { struct page *page = virt_to_head_page(addr); - if (unlikely(put_page_testzero(page))) - __free_pages_ok(page, compound_order(page)); + if (unlikely(put_page_testzero(page))) { + unsigned int order = compound_order(page); + + if (order == 0) + free_unref_page(page); + else + __free_pages_ok(page, order); + } } EXPORT_SYMBOL(page_frag_free);
page_frag_free() calls __free_pages_ok() to free the page back to Buddy. This is OK for high order page, but for order-0 pages, it misses the optimization opportunity of using Per-Cpu-Pages and can cause zone lock contention when called frequently. Paweł Staszewski recently shared his result of 'how Linux kernel handles normal traffic'[1] and from perf data, Jesper Dangaard Brouer found the lock contention comes from page allocator: mlx5e_poll_tx_cq | --16.34%--napi_consume_skb | |--12.65%--__free_pages_ok | | | --11.86%--free_one_page | | | |--10.10%--queued_spin_lock_slowpath | | | --0.65%--_raw_spin_lock | |--1.55%--page_frag_free | --1.44%--skb_release_data Jesper explained how it happened: mlx5 driver RX-page recycle mechanism is not effective in this workload and pages have to go through the page allocator. The lock contention happens during mlx5 DMA TX completion cycle. And the page allocator cannot keep up at these speeds.[2] I thought that __free_pages_ok() are mostly freeing high order pages and thought this is an lock contention for high order pages but Jesper explained in detail that __free_pages_ok() here are actually freeing order-0 pages because mlx5 is using order-0 pages to satisfy its page pool allocation request.[3] The free path as pointed out by Jesper is: skb_free_head() -> skb_free_frag() -> skb_free_frag() -> page_frag_free() And the pages being freed on this path are order-0 pages. Fix this by doing similar things as in __page_frag_cache_drain() - send the being freed page to PCP if it's an order-0 page, or directly to Buddy if it is a high order page. With this change, Paweł hasn't noticed lock contention yet in his workload and Jesper has noticed a 7% performance improvement using a micro benchmark and lock contention is gone. [1]: https://www.spinics.net/lists/netdev/msg531362.html [2]: https://www.spinics.net/lists/netdev/msg531421.html [3]: https://www.spinics.net/lists/netdev/msg531556.html Reported-by: Paweł Staszewski <pstaszewski@itcare.pl> Analysed-by: Jesper Dangaard Brouer <brouer@redhat.com> Signed-off-by: Aaron Lu <aaron.lu@intel.com> --- mm/page_alloc.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)