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

[Li, Xiaoyun]

> -----Original Message-----
> From: Thomas Monjalon [mailto:thomas at monjalon.net]
> Sent: Thursday, October 19, 2017 14:59
> To: Li, Xiaoyun <xiaoyun.li at intel.com>
> Cc: Ananyev, Konstantin <konstantin.ananyev at intel.com>; Richardson,
> Bruce <bruce.richardson at intel.com>; dev at dpdk.org; Lu, Wenzhuo
> <wenzhuo.lu at intel.com>; Zhang, Helin <helin.zhang at intel.com>;
> ophirmu at mellanox.com
> Subject: Re: [dpdk-dev] [PATCH v8 1/3] eal/x86: run-time dispatch over
> memcpy
> 
> 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.
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.

> > > 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?
> 
>