linux-kernel - Re: deadline ALWAYS default for dasd devices(s390) ?

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Date:	Thu, 06 May 2010 09:34:59 +0200
From:	Xose Vazquez Perez <xose.vazquez@...il.com>
To:	Stefan Weinhuber <wein@...ux.vnet.ibm.com>
CC:	Heiko Carstens <heiko.carstens@...ibm.com>,
	Stefan Weinhuber <wein@...ibm.com>,
	Horst Hummel <Horst.Hummel@...ibm.com>,
	Stefan Haberland <stefan.haberland@...ibm.com>,
	linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: deadline ALWAYS default for dasd devices(s390) ?

On 05/05/2010 09:52 AM, Stefan Weinhuber wrote:

hi,

> At the time this change was made we had the problem that the
> default scheduler chosen by the distributions resulted in
> bad performance for DASD devices.

Have you done recently new cfq vs. deadline tests, in z/VM
and LPAR ?

> I agree that hard coding this choice into the driver is not pretty,
> but it is pragmatic. 

It's awful. Easier and simpler from user space: /sys/block/dasdX/queue/scheduler

> Some generic mechanism for setting driver specific
> defaults would be nicer, but I doubt that many other drivers would
> actually benefit from such an interface.

see s390-tools-1.8.4/etc/udev/rules.d/60-readahead.rules
That's the way to do it.

-thanks-

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