linux-kernel - Re: question about splice performance

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Message-ID: <alpine.LNX.1.10.0805251736400.19084@fbirervta.pbzchgretzou.qr>
Date:	Sun, 25 May 2008 17:40:42 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	Francis Moreau <francis.moro@...il.com>
cc:	linux-kernel@...r.kernel.org, jens.axboe@...cle.com
Subject: Re: question about splice performance


On Sunday 2008-05-25 17:12, Francis Moreau wrote:

>Hi,
>
>I did a really basic benchmark and was suprise about the results.
>
>$ echo 3 > /proc/sys/vm/drop_caches
>$ time  splice-cp  vmlinux /tmp/vmlinux
>
>real    0m10.158s
>user    0m0.002s
>sys     0m0.401s
>
>$ echo 3 > /proc/sys/vm/drop_caches
>$ time  cp  vmlinux /tmp/vmlinux
>
>real    0m10.590s
>user    0m0.017s
>sys     0m0.459s
>
>
>I was expecting splice-cp case to be faster.
>
>Could someone enlight me ?

Slow disk outweighs memory copying overhead. And 300 MB is quickly
transferred in idle systems.
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