> -----Original Message----- > From: Thomas Monjalon [mailto:tho...@monjalon.net] > Sent: Wednesday, October 25, 2017 17:00 > To: Li, Xiaoyun <xiaoyun...@intel.com> > Cc: Ananyev, Konstantin <konstantin.anan...@intel.com>; Richardson, > Bruce <bruce.richard...@intel.com>; 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 > > 25/10/2017 10:54, Li, Xiaoyun: > > > > > > > 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. > > > > 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? > > > > > > As I already asked before - why not to make that threshold dynamic? > > > Konstantin > > > > > I want to confirm that raising threshold is useful. Then can make it dynamic > and set it very large as default. > > You can confirm it with micro-benchmarks.
I did tests on memcpy_perf_test. Set threshold to 1024. But when smaller than 1024 bytes, it costs 2~4 cycles more than the original. Such as original is 10, right now is 12. Then the drop is 2/12=16%. I don't know this kind of drop matters a lot or not. And above 1024 bytes, the drop is almost 4% as I said before. /Xiaoyun
