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-optimization-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? > > > > Another thing, I will test testpmd txonly with intel nics and > > > > mellanox these days. > > > > And try adjusting the RTE_X86_MEMCPY_THRESH to see if there is any > > > > improvement. > > > > > > > > > > Is there someone else seeing a performance degradation?
