Messages in this thread | | | From | Noah Goldstein <> | Date | Fri, 26 Nov 2021 13:14:32 -0600 | Subject | Re: [PATCH v1] x86/lib: Optimize 8x loop and memory clobbers in csum_partial.c |
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On Fri, Nov 26, 2021 at 12:50 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote: > > On Fri, Nov 26, 2021 at 12:27 PM Eric Dumazet <edumazet@google.com> wrote: > > > > On Fri, Nov 26, 2021 at 10:17 AM Noah Goldstein <goldstein.w.n@gmail.com> wrote: > > > > > > > > > > > Makes sense. Although if you inline I think you definitely will want a more > > > conservative clobber than just "memory". Also I think with 40 you also will > > > get some value from two counters. > > > > > > Did you see the number/question I posted about two accumulators for 32 > > > byte case? > > > Its a judgement call about latency vs throughput that I don't really have an > > > answer for. > > > > > > > The thing I do not know is if using more units would slow down the > > hyper thread ?
Did some quick tests with the latency/throughput benchmarks running in parallel on two hyperthreads on the same processors. The 32 byte case latency advantage goes with 2 accum and there is still a slight regression in throughput. The larger cases that hit the loop still still have improvements both in tput and latency with 2 accum.
> > There are more uops in the two accumulator version so it could be concern > iff the other hyperthread is bottlenecked on p06 throughput. My general > understanding is this is not the common case and that the very premise of > hyperthreads is that most bottlenecks are related to memory fetch or resolving > control flow. > > > > > Would using ADCX/ADOX would be better in this respect ? > > What would code using those instructions look like? Having trouble > seeing how to use them here.
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