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Date: Wed, 05 May 2010 11:55:11 +0400
From: Michael Tokarev <mjt@tls.msk.ru>
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To: Stefan Weinhuber <wein@linux.vnet.ibm.com>
CC: Heiko Carstens <heiko.carstens@de.ibm.com>,
       Xose Vazquez Perez <xose.vazquez@gmail.com>,
       Stefan Weinhuber <wein@de.ibm.com>,
       Horst Hummel <Horst.Hummel@de.ibm.com>,
       Stefan Haberland <stefan.haberland@de.ibm.com>,
       linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: deadline ALWAYS default for dasd devices(s390) ?
References: <4BD58848.8090205@gmail.com> <20100505061620.GA2381@osiris.boeblingen.de.ibm.com> <4BE123B1.1050500@linux.vnet.ibm.com>
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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