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SubjectRe: [PATCH] x86: Run checksumming in parallel accross multiple alu's

* Joe Perches <joe@perches.com> wrote:

> On Mon, 2013-10-14 at 15:44 -0700, Eric Dumazet wrote:
> > On Mon, 2013-10-14 at 15:37 -0700, Joe Perches wrote:
> > > On Mon, 2013-10-14 at 15:18 -0700, Eric Dumazet wrote:
> > > > attached patch brings much better results
> > > >
> > > > lpq83:~# ./netperf -H 7.7.8.84 -l 10 -Cc
> > > > MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 7.7.8.84 () port 0 AF_INET
> > > > Recv Send Send Utilization Service Demand
> > > > Socket Socket Message Elapsed Send Recv Send Recv
> > > > Size Size Size Time Throughput local remote local remote
> > > > bytes bytes bytes secs. 10^6bits/s % S % S us/KB us/KB
> > > >
> > > > 87380 16384 16384 10.00 8043.82 2.32 5.34 0.566 1.304
> > > >
> > > > diff --git a/arch/x86/lib/csum-partial_64.c b/arch/x86/lib/csum-partial_64.c
> > > []
> > > > @@ -68,7 +68,8 @@ static unsigned do_csum(const unsigned char *buff, unsigned len)
> > > > zero = 0;
> > > > count64 = count >> 3;
> > > > while (count64) {
> > > > - asm("addq 0*8(%[src]),%[res]\n\t"
> > > > + asm("prefetch 5*64(%[src])\n\t"
> > >
> > > Might the prefetch size be too big here?
> >
> > To be effective, you need to prefetch well ahead of time.
>
> No doubt.

So why did you ask then?

> > 5*64 seems common practice (check arch/x86/lib/copy_page_64.S)
>
> 5 cachelines for some processors seems like a lot.

What processors would that be?

Most processors have hundreds of cachelines even in their L1 cache.
Thousands in the L2 cache, up to hundreds of thousands.

Thanks,

Ingo


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