linux-kernel - Re: [PATCH v2 2/2] x86: add prefetching to do

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Message-ID: <20131106153429.GA26336@redhat.com>
Date:	Wed, 6 Nov 2013 10:34:29 -0500
From:	Dave Jones <davej@...hat.com>
To:	Neil Horman <nhorman@...driver.com>
Cc:	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 v2 2/2] x86: add prefetching to do_csum

On Wed, Nov 06, 2013 at 10:23:19AM -0500, Neil Horman wrote:
 > do_csum was identified via perf recently as a hot spot when doing
 > receive on ip over infiniband workloads.  After alot of testing and
 > ideas, we found the best optimization available to us currently is to
 > prefetch the entire data buffer prior to doing the checksum
 > 
 > diff --git a/arch/x86/lib/csum-partial_64.c b/arch/x86/lib/csum-partial_64.c
 > index 9845371..9f2d3ee 100644
 > --- a/arch/x86/lib/csum-partial_64.c
 > +++ b/arch/x86/lib/csum-partial_64.c
 > @@ -29,8 +29,15 @@ static inline unsigned short from32to16(unsigned a)
 >   * Things tried and found to not make it faster:
 >   * Manual Prefetching
 >   * Unrolling to an 128 bytes inner loop.
 > - * Using interleaving with more registers to break the carry chains.
 
Did you mean perhaps to remove the "Manual Prefetching" line instead ?
(Curious, what was tried before that made it not worthwhile?)
 
	Dave
 
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