linux-kernel - Re: Is splice() useful without page stealing?

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Message-ID: <20091218063454.GD32739@1wt.eu>
Date:	Fri, 18 Dec 2009 07:34:54 +0100
From:	Willy Tarreau <w@....eu>
To:	"Patrick J. LoPresti" <lopresti@...il.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Is splice() useful without page stealing?

On Thu, Dec 17, 2009 at 06:47:19PM -0800, Patrick J. LoPresti wrote:
(...)
> Now, if splice() actually let you do things like flip pages from the
> network stack into the page cache with zero copies, then I could see
> the point.  As it is, I am curious to know:
> 
> 1) Does anybody have any actual benchmarks showing performance
> advantages for splice() over read()/write()?   If so, can I obtain the
> benchmark code?

I did this for TCP->TCP sockets, and the gain is huge at high
bit rates (10 Gbps). Basically, 10 Gbps at 20% CPU with splice,
100% CPU with recv/send. You can find the test results here :

   http://haproxy.1wt.eu/10g.html

I'm not using splice for disk-to-net nor net-to-disk transfers though.

Willy

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