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

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Message-ID: <1381790278.16896.2.camel@joe-AO722>
Date:	Mon, 14 Oct 2013 15:37:58 -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 15:18 -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?

0x140 is pretty big and is always multiple cachelines no?

> +				    "addq 0*8(%[src]),%[res]\n\t"
>  				    "adcq 1*8(%[src]),%[res]\n\t"
>  				    "adcq 2*8(%[src]),%[res]\n\t"
>  				    "adcq 3*8(%[src]),%[res]\n\t"



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