netdev - RE: Splice status

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Message-ID: <EE71107DF0D1F24FA2D95041E64AB9E8ED254E7BAB@IL-MB01.marvell.com>
Date:	Tue, 13 Jul 2010 15:42:25 +0300
From:	Ofer Heifetz <oferh@...vell.com>
To:	Changli Gao <xiaosuo@...il.com>
CC:	Eric Dumazet <eric.dumazet@...il.com>,
	Jens Axboe <axboe@...nel.dk>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: Splice status

Write and re-write numbers are in MBps.
Iozone performs re-write meaning reads a chunk of data and writes it back, so basically the performance for this operation should be quiet high since kernel caches usage.

I forgot to mention that I used EXT4 fs.

-Ofer

-----Original Message-----
From: Changli Gao [mailto:xiaosuo@...il.com] 
Sent: Tuesday, July 13, 2010 3:32 PM
To: Ofer Heifetz
Cc: Eric Dumazet; Jens Axboe; netdev@...r.kernel.org
Subject: Re: Splice status

On Tue, Jul 13, 2010 at 7:41 PM, Ofer Heifetz <oferh@...vell.com> wrote:
> Hi,
>
> I wanted to let you know that I have been testing Samba splice on Marvell 6282 SoC on 2.6.35_rc3 and noticed that it gave worst performance than not using it and also noticed that on re-writing file the iowait is high.
>
> iometer using 2G file (file is created before test)
>
> Splice  write cpu% iow%
> -----------------------
>  No     58    98    0
> Yes     14   100   48
>
> iozone using 2G file (file created during test)
>
> Splice  write cpu% iow%  re-write cpu% iow%
> -------------------------------------------
>  No     35    85    4    58.2     70    0
> Yes     33    85    4    15.7    100   58
>
> Any clue why splice introduces a high iowait?
> I noticed samba uses up to 16K per splice syscall, changing the samba to try more did not help, so I guess it is a kernel limitation.
>
> -Ofer
>

What does the column write means? And what do you mean by saying
re-write? Thanks.

-- 
Regards,
Changli Gao(xiaosuo@...il.com)
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