Messages in this thread | | | Subject | Re: ARM router NAT performance affected by random/unrelated commits | From | Rafał Miłecki <> | Date | Wed, 22 May 2019 23:12:12 +0200 |
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On 22.05.2019 14:17, Russell King - ARM Linux admin wrote: > On Wed, May 22, 2019 at 01:51:01PM +0200, Rafał Miłecki wrote: >> On 21.05.2019 12:45, Russell King - ARM Linux admin wrote:> On Tue, May 21, 2019 at 12:28:48PM +0200, Rafał Miłecki wrote: >>>> I work on home routers based on Broadcom's Northstar SoCs. Those devices >>>> have ARM Cortex-A9 and most of them are dual-core. >>>> >>>> As for home routers, my main concern is network performance. That CPU >>>> isn't powerful enough to handle gigabit traffic so all kind of >>>> optimizations do matter. I noticed some unexpected changes in NAT >>>> performance when switching between kernels. >>>> >>>> My hardware is BCM47094 SoC (dual core ARM) with integrated network >>>> controller and external BCM53012 switch. >>> >>> Guessing, I'd say it's to do with the placement of code wrt cachelines. >>> You could try aligning some of the cache flushing code to a cache line >>> and see what effect that has. >> >> Is System.map a good place to check for functions code alignment? >> >> With Linux 4.19 + OpenWrt mtd patches I have: >> (...) >> c010ea94 t v7_dma_inv_range >> c010eae0 t v7_dma_clean_range >> (...) >> c02ca3d0 T blk_mq_update_nr_hw_queues >> c02ca69c T blk_mq_alloc_tag_set >> c02ca94c T blk_mq_release >> c02ca9b4 T blk_mq_free_queue >> c02caa88 T blk_mq_update_nr_requests >> c02cab50 T blk_mq_unique_tag >> (...) >> >> After cherry-picking 9316a9ed6895 ("blk-mq: provide helper for setting >> up an SQ queue and tag set"): >> (...) >> c010ea94 t v7_dma_inv_range >> c010eae0 t v7_dma_clean_range >> (...) >> c02ca3d0 T blk_mq_update_nr_hw_queues >> c02ca69c T blk_mq_alloc_tag_set >> c02ca94c T blk_mq_init_sq_queue <-- NEW >> c02ca9c0 T blk_mq_release <-- Different address of this & all below >> c02caa28 T blk_mq_free_queue >> c02caafc T blk_mq_update_nr_requests >> c02cabc4 T blk_mq_unique_tag >> (...) >> >> As you can see blk_mq_init_sq_queue has appeared in the System.map and >> it affected addresses of ~30000 symbols. I can believe some frequently >> used symbols got luckily aligned and that improved overall performance. >> >> Interestingly v7_dma_inv_range() and v7_dma_clean_range() were not >> relocated. >> >> ***** >> >> I followed Russell's suggestion and added .align 5 to cache-v7.S (see >> two attached diffs). >> >> 1) v4.19 + OpenWrt mtd patches >>> egrep -B 1 -A 1 "v7_dma_(inv|clean)_range" System.map >> c010ea58 T v7_flush_kern_dcache_area >> c010ea94 t v7_dma_inv_range >> c010eae0 t v7_dma_clean_range >> c010eb18 T b15_dma_flush_range >> >> 2) v4.19 + OpenWrt mtd patches + two .align 5 in cache-v7.S >> c010ea6c T v7_flush_kern_dcache_area >> c010eac0 t v7_dma_inv_range >> c010eb20 t v7_dma_clean_range >> c010eb58 T b15_dma_flush_range >> (actually 15 symbols above v7_dma_inv_range were replaced) >> >> This method seems to be somehow working (at least affects addresses in >> System.map). >> >> ***** >> >> I run 2 tests for each combination of changes. Each test consisted of >> 10 sequences of: 30 seconds iperf session + reboot. >> >> >>> git reset --hard v4.19 >>> git am OpenWrt-mtd-chages.patch >> Test #1: 738 Mb/s >> Test #2: 737 Mb/s >> >>> git reset --hard v4.19 >>> git am OpenWrt-mtd-chages.patch >> patch -p1 < v7_dma_clean_range-align.diff >> Test #1: 746 Mb/s >> Test #2: 747 Mb/s >> >>> git reset --hard v4.19 >>> git am OpenWrt-mtd-chages.patch >>> patch -p1 < v7_dma_inv_range-align.diff >> Test #1: 745 Mb/s >> Test #2: 746 Mb/s >> >>> git reset --hard v4.19 >>> git am OpenWrt-mtd-chages.patch >>> patch -p1 < v7_dma_clean_range-align.diff >>> patch -p1 < v7_dma_inv_range-align.diff >> Test #1: 762 Mb/s >> Test #2: 761 Mb/s >> >> As you can see I got a quite nice performance improvement after aligning >> both: v7_dma_clean_range() and v7_dma_inv_range(). > > This is an improvement of about 3.3%. > >> It still wasn't as good as with 9316a9ed6895 cherry-picked but pretty >> close. >> >> >>> git reset --hard v4.19 >>> git am OpenWrt-mtd-chages.patch >>> git cherry-pick -x 9316a9ed6895 >> Test #1: 770 Mb/s >> Test #2: 766 Mb/s >> >>> git reset --hard v4.19 >>> git am OpenWrt-mtd-chages.patch >>> git cherry-pick -x 9316a9ed6895 >>> patch -p1 < v7_dma_clean_range-align.diff >> Test #1: 756 Mb/s >> Test #2: 759 Mb/s >> >>> git reset --hard v4.19 >>> git am OpenWrt-mtd-chages.patch >>> git cherry-pick -x 9316a9ed6895 >>> patch -p1 < v7_dma_inv_range-align.diff >> Test #1: 758 Mb/s >> Test #2: 759 Mb/s >> >>> git reset --hard v4.19 >>> git am OpenWrt-mtd-chages.patch >>> git cherry-pick -x 9316a9ed6895 >>> patch -p1 < v7_dma_clean_range-align.diff >>> patch -p1 < v7_dma_inv_range-align.diff >> Test #1: 767 Mb/s >> Test #2: 763 Mb/s >> >> Now you can see how unpredictable it is. If I cherry-pick 9316a9ed6895 >> and do an extra alignment of v7_dma_clean_range() and v7_dma_inv_range() >> that extra alignment can actually *hurt* NAT performance. > > You have a maximum variance of 4Mb/s in your tests which is around > 0.5%, and this shows a reduction of 3Mb/s, or 0.4%. > > If we look at it a different way: > - Without the alignment patches, there is a difference of 4% in > performance depending on whether 9316a9ed6895 is applied. > - With the alignment patches, there is a difference of 0.4% in > performance depending on whether 9316a9ed6895 is applied. > > How can this not be beneficial?
Aligning v7_dma_clean_range() and v7_dma_inv_range() is definitely beneficial! I'm sorry I wasn't clear enough.
I redid testing of 2 most important setups with few more iterations.
> git reset --hard v4.19 > git am OpenWrt-mtd-chages.patch > git cherry-pick -x 9316a9ed6895 [ 3] 0.0-30.0 sec 2.71 GBytes 776 Mbits/sec [ 3] 0.0-30.0 sec 2.71 GBytes 775 Mbits/sec [ 3] 0.0-30.0 sec 2.70 GBytes 774 Mbits/sec [ 3] 0.0-30.0 sec 2.70 GBytes 774 Mbits/sec [ 3] 0.0-30.0 sec 2.70 GBytes 773 Mbits/sec [ 3] 0.0-30.0 sec 2.70 GBytes 773 Mbits/sec [ 3] 0.0-30.0 sec 2.70 GBytes 773 Mbits/sec [ 3] 0.0-30.0 sec 2.69 GBytes 771 Mbits/sec [ 3] 0.0-30.0 sec 2.69 GBytes 771 Mbits/sec [ 3] 0.0-30.0 sec 2.69 GBytes 771 Mbits/sec [ 3] 0.0-30.0 sec 2.69 GBytes 771 Mbits/sec [ 3] 0.0-30.0 sec 2.69 GBytes 770 Mbits/sec [ 3] 0.0-30.0 sec 2.69 GBytes 770 Mbits/sec [ 3] 0.0-30.0 sec 2.69 GBytes 770 Mbits/sec [ 3] 0.0-30.0 sec 2.69 GBytes 770 Mbits/sec [ 3] 0.0-30.0 sec 2.69 GBytes 769 Mbits/sec [ 3] 0.0-30.0 sec 2.69 GBytes 769 Mbits/sec [ 3] 0.0-30.0 sec 2.68 GBytes 768 Mbits/sec [ 3] 0.0-30.0 sec 2.68 GBytes 768 Mbits/sec [ 3] 0.0-30.0 sec 2.68 GBytes 767 Mbits/sec [ 3] 0.0-30.0 sec 2.68 GBytes 767 Mbits/sec [ 3] 0.0-30.0 sec 2.68 GBytes 767 Mbits/sec [ 3] 0.0-30.0 sec 2.67 GBytes 765 Mbits/sec [ 3] 0.0-30.0 sec 2.67 GBytes 765 Mbits/sec [ 3] 0.0-30.0 sec 2.67 GBytes 764 Mbits/sec [ 3] 0.0-30.0 sec 2.67 GBytes 763 Mbits/sec [ 3] 0.0-30.0 sec 2.67 GBytes 763 Mbits/sec [ 3] 0.0-30.0 sec 2.66 GBytes 762 Mbits/sec [ 3] 0.0-30.0 sec 2.66 GBytes 760 Mbits/sec [ 3] 0.0-30.0 sec 2.66 GBytes 760 Mbits/sec Average: 769 Mb/s (+4,10%) Previous results: 773 Mb/s, 770 Mb/s, 766 Mb/s
> git reset --hard v4.19 > git am OpenWrt-mtd-chages.patch > patch -p1 < v7_dma_clean_range-align.diff > patch -p1 < v7_dma_inv_range-align.diff [ 3] 0.0-30.0 sec 2.69 GBytes 769 Mbits/sec [ 3] 0.0-30.0 sec 2.69 GBytes 769 Mbits/sec [ 3] 0.0-30.0 sec 2.68 GBytes 767 Mbits/sec [ 3] 0.0-30.0 sec 2.68 GBytes 766 Mbits/sec [ 3] 0.0-30.0 sec 2.67 GBytes 766 Mbits/sec [ 3] 0.0-30.0 sec 2.67 GBytes 765 Mbits/sec [ 3] 0.0-30.0 sec 2.67 GBytes 765 Mbits/sec [ 3] 0.0-30.0 sec 2.67 GBytes 765 Mbits/sec [ 3] 0.0-30.0 sec 2.67 GBytes 764 Mbits/sec [ 3] 0.0-30.0 sec 2.67 GBytes 763 Mbits/sec [ 3] 0.0-30.0 sec 2.67 GBytes 763 Mbits/sec [ 3] 0.0-30.0 sec 2.66 GBytes 762 Mbits/sec [ 3] 0.0-30.0 sec 2.66 GBytes 762 Mbits/sec [ 3] 0.0-30.0 sec 2.66 GBytes 762 Mbits/sec [ 3] 0.0-30.0 sec 2.66 GBytes 762 Mbits/sec [ 3] 0.0-30.0 sec 2.66 GBytes 761 Mbits/sec [ 3] 0.0-30.0 sec 2.66 GBytes 761 Mbits/sec [ 3] 0.0-30.0 sec 2.66 GBytes 760 Mbits/sec [ 3] 0.0-30.0 sec 2.66 GBytes 760 Mbits/sec [ 3] 0.0-30.0 sec 2.66 GBytes 760 Mbits/sec [ 3] 0.0-30.0 sec 2.65 GBytes 760 Mbits/sec [ 3] 0.0-30.0 sec 2.65 GBytes 759 Mbits/sec [ 3] 0.0-30.0 sec 2.65 GBytes 759 Mbits/sec [ 3] 0.0-30.0 sec 2.65 GBytes 758 Mbits/sec [ 3] 0.0-30.0 sec 2.65 GBytes 758 Mbits/sec [ 3] 0.0-30.0 sec 2.65 GBytes 757 Mbits/sec [ 3] 0.0-30.0 sec 2.65 GBytes 757 Mbits/sec [ 3] 0.0-30.0 sec 2.65 GBytes 757 Mbits/sec [ 3] 0.0-30.0 sec 2.64 GBytes 757 Mbits/sec [ 3] 0.0-30.0 sec 2.64 GBytes 756 Mbits/sec Average: 762 Mb/s (+3,16%) Previous results: 767 Mb/s, 763 Mb/s
So let me explain why I keep researching on this. There are two reasons:
1) Realignment done by cherry-picking 9316a9ed6895 was providing a *marginally* better performance than aligning v7_dma_clean_range() and v7_dma_inv_range(). It's a *very* minimal difference but I can't stop thinking I can still do better.
2) Cherry-picking 9316a9ed6895 doesn't change v7_dma_clean_range or v7_dma_inv_range addresses at all. Yet it still improves NAT performance. That makes me believe there are more functions that (if properly aligned) can bump NAT performance. I hope that aligning all: * v7_dma_clean_range * v7_dma_inv_range * [some unrevealed functions] could result in even better NAT performance.
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