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

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Message-ID: <20131101173701.GC8467@hmsreliant.think-freely.org>
Date:	Fri, 1 Nov 2013 13:37:01 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	Ben Hutchings <bhutchings@...arflare.com>,
	Doug Ledford <dledford@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] x86: Run checksumming in parallel accross multiple alu's

On Fri, Nov 01, 2013 at 04:18:50PM -0000, David Laight wrote:
> > How would you suggest replacing the jumps in this case?  I agree it would be
> > faster here, but I'm not sure how I would implement an increment using a single
> > conditional move.
> 
> I think you need 3 instructions, move a 0, conditionally move a 1
> then add. I suspect it won't be a win!
> 
> If you do 'win' it is probably very dependent on how the instructions
> get scheduled onto the execution units - which will probably make
> it very cpu type dependant.
> 
> 	David
> 
I agree, that sounds interesting, but very cpu dependent.  Thanks for the
suggestion, Ben, but I think it would be better if we just did the prefetch here
and re-addressed this area when AVX (or addcx/addox) instructions were available
for testing on hardware.

Neil

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