25/10/2017 09:25, Thomas Monjalon: > 25/10/2017 08:55, Li, Xiaoyun: > > From: Li, Xiaoyun > > > From: Richardson, Bruce > > > > On Thu, Oct 19, 2017 at 11:00:33AM +0200, Thomas Monjalon wrote: > > > > > 19/10/2017 10:50, Li, Xiaoyun: > > > > > > From: Thomas Monjalon > > > > > > > 19/10/2017 09:51, Li, Xiaoyun: > > > > > > > > From: Thomas Monjalon [mailto:tho...@monjalon.net] > > > > > > > > > 19/10/2017 04:45, Li, Xiaoyun: > > > > > > > > > > Hi > > > > > > > > > > > > > > > > > > > > > > > > > > The significant change of this patch is to call a > > > > > > > > > > > > > function pointer for packet size > 128 > > > > (RTE_X86_MEMCPY_THRESH). > > > > > > > > > > > > The perf drop is due to function call replacing inline. > > > > > > > > > > > > > > > > > > > > > > > > > Please could you provide some benchmark numbers? > > > > > > > > > > > > I ran memcpy_perf_test which would show the time cost > > > > > > > > > > > > of memcpy. I ran it on broadwell with sse and avx2. > > > > > > > > > > > > But I just draw pictures and looked at the trend not > > > > > > > > > > > > computed the exact percentage. Sorry about that. > > > > > > > > > > > > The picture shows results of copy size of 2, 4, 6, 8, > > > > > > > > > > > > 9, 12, 16, 32, 64, 128, 192, 256, 320, 384, 448, 512, > > > > > > > > > > > > 768, 1024, 1518, 1522, 1536, 1600, 2048, 2560, 3072, > > > > > > > > > > > > 3584, 4096, 4608, 5120, 5632, 6144, 6656, 7168, > > > > > > > > > > > 7680, 8192. > > > > > > > > > > > > In my test, the size grows, the drop degrades. (Using > > > > > > > > > > > > copy time indicates the > > > > > > > > > > > > perf.) From the trend picture, when the size is > > > > > > > > > > > > smaller than > > > > > > > > > > > > 128 bytes, the perf drops a lot, almost 50%. And above > > > > > > > > > > > > 128 bytes, it approaches the original dpdk. > > > > > > > > > > > > I computed it right now, it shows that when greater > > > > > > > > > > > > than > > > > > > > > > > > > 128 bytes and smaller than 1024 bytes, the perf drops > > > > > > > > > > > > about > > > > 15%. > > > > > > > > > > > > When above > > > > > > > > > > > > 1024 bytes, the perf drops about 4%. > > > > > > > > > > > > > > > > > > > > > > > > > From a test done at Mellanox, there might be a > > > > > > > > > > > > > performance degradation of about 15% in testpmd > > > > > > > > > > > > > txonly > > > > with AVX2. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I did tests on X710, XXV710, X540 and MT27710 but didn't > > > > > > > > > > see > > > > > > > > > performance degradation. > > > > > > > > > > > > > > > > > > > > I used command "./x86_64-native-linuxapp-gcc/app/testpmd > > > > > > > > > > -c 0xf -n > > > > > > > > > > 4 -- - > > > > > > > > > I" and set fwd txonly. > > > > > > > > > > I tested it on v17.11-rc1, then revert my patch and tested > > > > > > > > > > it > > > again. > > > > > > > > > > Show port stats all and see the throughput pps. But the > > > > > > > > > > results are similar > > > > > > > > > and no drop. > > > > > > > > > > > > > > > > > > > > Did I miss something? > > > > > > > > > > > > > > > > > > I do not understand. Yesterday you confirmed a 15% drop with > > > > > > > > > buffers between > > > > > > > > > 128 and 1024 bytes. > > > > > > > > > But you do not see this drop in your txonly tests, right? > > > > > > > > > > > > > > > > > Yes. The drop is using test. > > > > > > > > Using command "make test -j" and then " ./build/app/test -c f > > > > > > > > -n 4 " > > > > > > > > Then run "memcpy_perf_autotest" > > > > > > > > The results are the cycles that memory copy costs. > > > > > > > > But I just use it to show the trend because I heard that it's > > > > > > > > not > > > > > > > recommended to use micro benchmarks like test_memcpy_perf for > > > > > > > memcpy performance report as they aren't likely able to reflect > > > > > > > performance of real world applications. > > > > > > > > > > > > > > Yes real applications can hide the memcpy cost. > > > > > > > Sometimes, the cost appear for real :) > > > > > > > > > > > > > > > Details can be seen at > > > > > > > > https://software.intel.com/en-us/articles/performance-optimiza > > > > > > > > ti > > > > > > > > on-of- > > > > > > > > memcpy-in-dpdk > > > > > > > > > > > > > > > > And I didn't see drop in testpmd txonly test. Maybe it's > > > > > > > > because not a lot > > > > > > > memcpy calls. > > > > > > > > > > > > > > It has been seen in a mlx4 use-case using more memcpy. > > > > > > > I think 15% in micro-benchmark is too much. > > > > > > > What can we do? Raise the threshold? > > > > > > > > > > > > > I think so. If there is big drop, can try raise the threshold. > > > > > > Maybe 1024? > > > > but not sure. > > > > > > But I didn't reproduce the 15% drop on mellanox and not sure how > > > > > > to > > > > verify it. > > > > > > > > > > I think we should focus on micro-benchmark and find a reasonnable > > > > > threshold for a reasonnable drop tradeoff. > > > > > > > > > Sadly, it may not be that simple. What shows best performance for > > > > micro- benchmarks may not show the same effect in a real application. > > > > > > > > /Bruce > > > > > > Then how to measure the performance? > > > > > > And I cannot reproduce 15% drop on mellanox. > > > Could the person who tested 15% drop help to do test again with 1024 > > > threshold and see if there is any improvement? > > > > As Bruce said, best performance on micro-benchmark may not show the same > > effect in real applications. > > Yes real applications may hide the impact. > You keep saying that it is a reason to allow degrading memcpy raw perf. > But can you see better performance with buffers of 256 bytes with > any application thanks to your patch? > I am not sure whether there is a benefit keeping a code which imply > a signicative drop in micro-benchmarks. > > > And I cannot reproduce the 15% drop. > > And I don't know if raising the threshold can improve the perf or not. > > Could the person who tested 15% drop help to do test again with 1024 > > threshold and see if there is any improvement? > > We will test a increased threshold today.
Sorry, I forgot to update. It seems that increasing the threshold from 128 to 1024 has no impact. We can recover the 15% drop only by reverting the patch. I don't know what is creating this drop exactly. When doing different tests on different environments, we do not see this drop. If nobody else can see such issue, I guess we can ignore it.
