netdev - Re: [PATCH v2 net-next] net: Implement fast csum_partial for x86

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Date:	Tue, 05 Jan 2016 19:21:11 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Tom Herbert <tom@...bertland.com>, davem@...emloft.net,
	netdev@...r.kernel.org, kernel-team@...com, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, x86@...nel.org
Subject: Re: [PATCH v2 net-next] net: Implement fast csum_partial for x86_64

On Wed, 2016-01-06 at 00:35 +0100, Hannes Frederic Sowa wrote:

> 
> Tom, did you have a look if it makes sense to add a second carry 
> addition train with the adcx instruction, which does not signal carry 
> via the carry flag but with the overflow flag? This instruction should 
> not have any dependencies with  the adc instructions and could help the 
> CPU to parallelize the code even more (increased instructions per cycle).

I guess adcx would (possibly) bring improvements for large areas, but
for this case the bottleneck is to bring data from memory.

Note this topic was discussed 2 years ago and no conclusive action was
taken.

https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg529610.html





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