From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758669Ab2DJSxW (ORCPT ); Tue, 10 Apr 2012 14:53:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:17312 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758353Ab2DJSxV (ORCPT ); Tue, 10 Apr 2012 14:53:21 -0400 Date: Tue, 10 Apr 2012 14:53:18 -0400 From: Vivek Goyal To: Jens Axboe Cc: linux kernel mailing list , Moyer Jeff Moyer Subject: Re: [RFC PATCH] block: Change default IO scheduler to deadline except SATA Message-ID: <20120410185318.GL21801@redhat.com> References: <20120410133708.GE21801@redhat.com> <4F843C17.5050004@kernel.dk> <20120410142148.GG21801@redhat.com> <20120410151042.GH21801@redhat.com> <4F847EC4.7040604@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4F847EC4.7040604@kernel.dk> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 10, 2012 at 08:41:08PM +0200, Jens Axboe wrote: [..] > > So we are back to the question of can scsi devices find out if a Lun > > is backed by single disk or multiple disks. > > The cleanest would be to have the driver signal these attributes at > probe time. You could even adjust CFQ properties based on this, driving > the queue depth harder etc. Realistically, going forward, most fast > flash devices will be driven by a noop-like scheduler on multiqueue. So > CPU cost of the IO scheduler can mostly be ignored, since CFQ cost on > even big RAIDs isn't an issue due to the low IOPS rates. Agreed that on RAID CPU cost is not a problem. Just that idling and low queue depth kills the performance. So apart from "rotational" if driver can give some hints about underlying devices being RAID (or multi device), it will help. Just that it looks like scsi does not have a way to determine that. Thanks Vivek