Re: [PATCH v8 1/3] eal/x86: run-time dispatch over memcpy

[Thomas Monjalon <thomas@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?

> > 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?