> -----Original Message----- > From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Li, Xiaoyun > Sent: Wednesday, October 18, 2017 10:22 > To: Thomas Monjalon <tho...@monjalon.net>; Ananyev, Konstantin > <konstantin.anan...@intel.com>; Richardson, Bruce > <bruce.richard...@intel.com> > Cc: dev@dpdk.org; Lu, Wenzhuo <wenzhuo...@intel.com>; Zhang, Helin > <helin.zh...@intel.com>; ophi...@mellanox.com > Subject: Re: [dpdk-dev] [PATCH v8 1/3] eal/x86: run-time dispatch over > memcpy > > Hi > > > -----Original Message----- > > From: Thomas Monjalon [mailto:tho...@monjalon.net] > > Sent: Wednesday, October 18, 2017 05:24 > > To: Li, Xiaoyun <xiaoyun...@intel.com>; Ananyev, Konstantin > > <konstantin.anan...@intel.com>; Richardson, Bruce > > <bruce.richard...@intel.com> > > Cc: dev@dpdk.org; Lu, Wenzhuo <wenzhuo...@intel.com>; Zhang, Helin > > <helin.zh...@intel.com>; ophi...@mellanox.com > > Subject: Re: [dpdk-dev] [PATCH v8 1/3] eal/x86: run-time dispatch over > > memcpy > > > > Hi, > > > > 13/10/2017 11:01, Xiaoyun Li: > > > This patch dynamically selects functions of memcpy at run-time based > > > on CPU flags that current machine supports. This patch uses function > > > pointers which are bind to the relative functions at constrctor time. > > > In addition, AVX512 instructions set would be compiled only if users > > > config it enabled and the compiler supports it. > > > > > > Signed-off-by: Xiaoyun Li <xiaoyun...@intel.com> > > > --- > > Keeping only the major changes of the patch for later discussions: > > [...] > > > static inline void * > > > rte_memcpy(void *dst, const void *src, size_t n) { > > > - if (!(((uintptr_t)dst | (uintptr_t)src) & ALIGNMENT_MASK)) > > > - return rte_memcpy_aligned(dst, src, n); > > > + if (n <= RTE_X86_MEMCPY_THRESH) > > > + return rte_memcpy_internal(dst, src, n); > > > else > > > - return rte_memcpy_generic(dst, src, n); > > > + return (*rte_memcpy_ptr)(dst, src, n); > > > } > > [...] > > > +static inline void * > > > +rte_memcpy_internal(void *dst, const void *src, size_t n) { > > > + if (!(((uintptr_t)dst | (uintptr_t)src) & ALIGNMENT_MASK)) > > > + return rte_memcpy_aligned(dst, src, n); > > > + else > > > + return rte_memcpy_generic(dst, src, n); } > > > > 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.
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?
