linux-kernel - Re: [PATCH] x86: Run checksumming in parallel accross multiple alu's

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Date:	Mon, 14 Oct 2013 15:49:42 -0700
From:	Joe Perches <joe@...ches.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Neil Horman <nhorman@...driver.com>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	sebastien.dugue@...l.net, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Re: [PATCH] x86: Run checksumming in parallel accross multiple alu's

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.

> 5*64 seems common practice (check arch/x86/lib/copy_page_64.S)

5 cachelines for some processors seems like a lot.

Given you've got a test rig, maybe you could experiment
with 2 and increase it until it doesn't get better.

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