From: "Alan D. Brunelle" <Alan.Brunelle@hp.com>
To: john smith <whalajam@yahoo.com>
Cc: fio@vger.kernel.org
Subject: Re: io scheduler merges control
Date: Mon, 04 Jan 2010 09:34:07 -0500 [thread overview]
Message-ID: <1262615647.3908.3.camel@cail> (raw)
In-Reply-To: <328428.66762.qm@web55006.mail.re4.yahoo.com>
On Thu, 2009-12-24 at 11:12 -0800, john smith wrote:
> IOPS-reported numbers for a test vary (more than 30% in my case) from one run to another depending on kernel io scheduler merges (reported in "Disk stats/merges=reads/writes") making it hard to measure/compare performance of block drivers, for instance.
>
> I don't see any way to turn off kernel io scheduler merges (cfq or others)
> and I'd ask if you would consider adding support for it, disabling the merges per individual device, using sys-fs maybe?
>
> If you do, adding an option to fio for controlling the merges would be useful too,
>
> thanks,
> John
Hi John -
FYI: there is /sys/block/*/queue/nomerges - when set to one ('echo 1
> /sys/block/<dsf>/queue/nomerges) - a lot of the merging attempts are
not performed. [Note, _some_ simple merge attempts _are_ still attempted
regardless of its setting...]
Regards,
Alan
next prev parent reply other threads:[~2010-01-04 14:34 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-12-24 19:12 io scheduler merges control john smith
2010-01-04 14:34 ` Alan D. Brunelle [this message]
2010-01-05 1:53 ` john smith
2010-01-05 16:32 ` Alan D. Brunelle
2010-01-11 13:54 ` Jens Axboe
2010-01-14 18:37 ` john smith
2010-01-20 16:18 ` Alan D. Brunelle
2010-01-20 23:57 ` john smith
2010-01-11 6:15 ` Gurudas Pai
2010-01-11 13:52 ` Jens Axboe
2010-01-04 14:52 ` Chris Worley
2010-01-05 0:27 ` john smith
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