On Fri, Aug 01, 2014 at 01:56:24PM +0000, Ananyev, Konstantin wrote: > > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Neil Horman > > Sent: Friday, August 01, 2014 2:37 PM > > To: Richardson, Bruce > > Cc: dev at dpdk.org > > Subject: Re: [dpdk-dev] [PATCH 0/2] dpdk: Allow for dynamic enablement of > > some isolated features > > > > On Thu, Jul 31, 2014 at 01:19:50PM -0700, Bruce Richardson wrote: > > > 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. :-) > > > > > > > > > Wait a moment, I'm not entirely sure what you did here. I understand that > > you > > replaced the _mm_popcnt_u64 call in the ixgbe pmd vector receive path with > > __builtin_popcnt, which is good, but ixgbe also uses the __mm_shuffle_epi8 > > intrinsic which is only available with sse4.2 from what I can see. did you > > replace those calls with a __builtin_shuffle variant? Otherwise, how did > > you > > get the pmd to build? I'm asking because this is what I tried in the first > > pass > > and Konstantin gave some pretty convicing evidence that this was an > > unworkable > > solution: > > http://dpdk.org/ml/archives/dev/2014-July/004443.html > > > > I think that _mm_shuffle_epi8 (PSHUFB) is available starting from SSE3. > So I presume, there is no need for replacement. Ah, I see, its just because we're using the nmmintrinsic.h header. We need to replace the popcount instruction and change the include header to tmmintrins.h to avoid the #error from the failed sse4.2 check
Thanks! Neil > Konstantin >
