From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755323Ab0ITXzk (ORCPT ); Mon, 20 Sep 2010 19:55:40 -0400 Received: from mga02.intel.com ([134.134.136.20]:56801 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754531Ab0ITXz3 (ORCPT ); Mon, 20 Sep 2010 19:55:29 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.56,396,1280732400"; d="scan'208";a="556449477" Subject: Re: [patch]cfq-iosched: don't idle if a deep seek queue is slow From: Shaohua Li To: Vivek Goyal Cc: lkml , "jaxboe@fusionio.com" , "czoccolo@gmail.com" In-Reply-To: <20100920141541.GE6138@redhat.com> References: <1284972814.6598.18.camel@sli10-conroe.sh.intel.com> <20100920141541.GE6138@redhat.com> Content-Type: text/plain; charset="UTF-8" Date: Tue, 21 Sep 2010 07:55:07 +0800 Message-ID: <1285026907.1668.6.camel@shli-laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2010-09-20 at 22:15 +0800, Vivek Goyal wrote: > On Mon, Sep 20, 2010 at 04:53:34PM +0800, Shaohua Li wrote: > > If a deep seek queue slowly deliver requests but disk is much faster, idle > > for the queue just wastes disk throughput. If the queue delevers all requests > > before half its slice is used, the patch disable idle for it. > > In my test, application delivers 32 requests one time, the disk can accept > > 128 requests at maxium and disk is fast. without the patch, the throughput > > is just around 30m/s, while with it, the speed is about 80m/s. The disk is > > a SSD, but is detected as a rotational disk. I can configure it as SSD, but > > I thought the deep seek queue logic should be fixed too, for example, > > considering a fast raid. > > > > Hi Shaohua, > > So you seem to be addressing the issue of storage being fast enough and > a single queue not being able to keep the storage busy. > > But we have the same issue for non-deep queues for a fast storage. This > patch will not solve that. right. > I think CFQ idling in general is a problem on faster storage. For SSDs we > can statically detect non-rotational media and disable idling. For faster > RAIDs we need to find an intellligent way of detection and disable idling. > > One of the suggestions at this year's LSF was to keep idling on only for > SATA disks and for any SCSI disks we can think of disabling idling by > default. May be with the help of udev rule. That makes sense, but shouldn't kernel has some reasonable setting? completely depending on userspace isn't reliable. Thanks, Shaohua