From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bruce Richardson Subject: Re: [PATCH 0/2] dpdk: Allow for dynamic enablement of some isolated features Date: Thu, 31 Jul 2014 13:19:50 -0700 Message-ID: <20140731201949.GA28495@localhost.localdomain> References: <1406665466-29654-1-git-send-email-nhorman@tuxdriver.com> <20140730210920.GB6420@localhost.localdomain> <20140731131351.GA20718@hmsreliant.think-freely.org> <5766264.li3nkTmgY6@xps13> <20140731143228.GB20718@hmsreliant.think-freely.org> <20140731181032.GC20718@hmsreliant.think-freely.org> <20140731183631.GC6420@localhost.localdomain> <20140731190117.GD20718@hmsreliant.think-freely.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: dev-VfR2kkLFssw@public.gmane.org To: Neil Horman Return-path: Content-Disposition: inline In-Reply-To: <20140731190117.GD20718-B26myB8xz7F8NnZeBjwnZQMhkBWG/bsMQH7oEaQurus@public.gmane.org> List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces-VfR2kkLFssw@public.gmane.org Sender: "dev" On Thu, Jul 31, 2014 at 03:01:17PM -0400, Neil Horman wrote: > On Thu, Jul 31, 2014 at 11:36:32AM -0700, Bruce Richardson wrote: > > > > I think a good first step here that I can't see anyone objecting to is > > to enable the ixgbe driver to use the vector code path for a generic > > x86_64 build. I've run a quick test here, and changing "_mm_popcnt_u64" > > to "__builtin_popcountll" [and the include from nmmintrin to tmmintrin] > > allows a compile for machine type default, and testpmd can still forward > > packets at a good rate (roughly perf down about 10% vs native compile on > > SNB). > > The ACL is a tougher nut to crack, but anyone see any issues with that > > two-line change to ixgbe_rxtx_vec.c? [Neil, since you started the patch > > set thread, do you want to submit an official patch here, or would you prefer I > > do so?] > > > > I'm happy to do so, Though 10% performance degradation vs. using the sse4.2 > instructions in that path seems significant, isn't it? Given that performance > delta, it seems like it would still be preferable to have a path that used the > sse4.2 instructions when they're available. Or am I misreading what you mean > when you say down 10% > > Neil > Ok, I did a little bit more testing here. Using the vector pmd compiled for generic x86_64 and using __builtin_popcountll is approx 35% faster for packet IO than the existing fast-path functions. It is also 7% (a bit lower than ~10% as I originally stated) slower than the existing native-compiled vpmd on a Sandy Bridge platform. I then ran an extra test, using EXTRA_CFLAGS='-msse4.2' to turn on the extra instructions. The ~7% performance drop went to ~3%, so we would gain a little more with using SSE4.2, but compared to the gain from having the vector driver at all, it's not that much. [I don't have a system handy with AVX2 support to see what boosts might come from compiling with that instruction set enabled.] Because of this, I'd take the ~35% speed boost for now, and try and find what would be the best general way to solve this problem across all libraries. Also, I think that anyone who needs that extra 4% performance probably wants the other 3% too, and so will compile up the code from source using the "native" compilation target. :-) /Bruce