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

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Date:	Wed, 05 May 2010 11:55:11 +0400
From:	Michael Tokarev <mjt@....msk.ru>
To:	Stefan Weinhuber <wein@...ux.vnet.ibm.com>
CC:	Heiko Carstens <heiko.carstens@...ibm.com>,
	Xose Vazquez Perez <xose.vazquez@...il.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) ?

05.05.2010 11:52, Stefan Weinhuber wrote:
>> On Mon, Apr 26, 2010 at 02:34:16PM +0200, Xose Vazquez Perez wrote:
>>> hi,
>>>
>>> why is it FORCED ? bypassing a GLOBAL setting and also the kernel
>>> command line !!!
>
> 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.
> I don't know what options were considered back then, but
> I think that having the device driver set a driver specific default
> is better than forcing the whole system to use 'our' scheduler.
>
> I agree that hard coding this choice into the driver is not pretty,
> but it is pragmatic. 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 also another thread started just two days ago:

  http://lkml.org/lkml/2010/5/3/404

Just... one more data point... ;)

/mjt
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