From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758309Ab0EEHwW (ORCPT ); Wed, 5 May 2010 03:52:22 -0400 Received: from mtagate4.uk.ibm.com ([194.196.100.164]:54085 "EHLO mtagate4.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756879Ab0EEHwU (ORCPT ); Wed, 5 May 2010 03:52:20 -0400 Message-ID: <4BE123B1.1050500@linux.vnet.ibm.com> Date: Wed, 05 May 2010 09:52:17 +0200 From: Stefan Weinhuber User-Agent: Thunderbird 2.0.0.24 (X11/20100317) MIME-Version: 1.0 To: Heiko Carstens CC: Xose Vazquez Perez , Stefan Weinhuber , Horst Hummel , Stefan Haberland , 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> In-Reply-To: <20100505061620.GA2381@osiris.boeblingen.de.ibm.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Heiko Carstens 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 !!! >> > > Horst, Stefan W. or Stefan H. should be able to answer your question. 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.