linux-kernel - Re: io-scheduler tuning for better read/write ratio

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Date:	Thu, 25 Jun 2009 16:45:40 +0300
From:	Al Boldi <a1426z@...ab.com>
To:	Ralf Gross <Ralf-Lists@...fgross.de>
Cc:	linux-kernel@...r.kernel.org, fengguang.wu@...el.com
Subject: Re: io-scheduler tuning for better read/write ratio

Ralf Gross wrote:
> Al Boldi schrieb:
> > Try changing /proc/sys/vm/dirty_ratio = 1
>
> $cat /proc/sys/vm/dirty_ratio
> 1
>
>
> $dstat -D md1 -d 5
> --dsk/md1--
> _read _writ
>   18M   18M
>    0     0
>  820k  101M
>   18M  113M
>   26M   73M
>   26M  110M
>   32M  100M
>   19M  111M
>   13M  117M
>   13M  142M
>   32M   88M
>   26M   99M
>   38M   58M
>
> No change. Even setting dirty_ratio to 100 didn't show any difference.

What's your readahead?  Do a blockdev --getra /dev/sdX and /dev/mdX.
Try increasing it, while keeping dirty_ratio low.


Thanks!

--
Al


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