netdev - Re: [RFC] csum experts, csum_replace2() is too expensive

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Message-ID: <20140321001303.GB20397@gondor.apana.org.au>
Date:	Fri, 21 Mar 2014 08:13:03 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Patrick McHardy <kaber@...sh.net>,
	"H.K. Jerry Chu" <hkchu@...gle.com>,
	Michael Dalton <mwdalton@...gle.com>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [RFC] csum experts, csum_replace2() is too expensive

On Thu, Mar 20, 2014 at 11:49:01AM -0700, Eric Dumazet wrote:
> csum_replace2() uses about 29 cycles, while a plain ip_send_check() is
> way faster (16 cycles)
> 
> csum_partial() is not really meant for doing checksums over 8 bytes !
> 
> Any idea how to make the thing really fast as intended ?
> 
> I saw csum_partial() consuming 1% of cpu cycles in a GRO workload, that
> is insane...
> 
> Following patch might be the fastest thing ?

Your patch makes sense to me.  However does it actually help
your 1% in the GRO profile?

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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