Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758168Ab0G2T5w (ORCPT ); Thu, 29 Jul 2010 15:57:52 -0400 Received: from mail-ww0-f44.google.com ([74.125.82.44]:58253 "EHLO mail-ww0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757894Ab0G2T5t convert rfc822-to-8bit (ORCPT ); Thu, 29 Jul 2010 15:57:49 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=PVezscbelB+e4HWUvYzz3Were2M+JbXAbhTrcyiMS5Xe6j5wlmD66PuHIyW6zkfp2g Ckf4WfDDAyi70V5Sc5NXeQ/6pSJ4DEvEDsUq36skqDS/ErUoH7zTrGhgYgvPtoEfb1rI jruYfSHiotFNNCJ6tJFiJfM+PkWxiFcJgCtkA= MIME-Version: 1.0 In-Reply-To: <20100726143300.GG12449@redhat.com> References: <1279739181-24482-1-git-send-email-vgoyal@redhat.com> <20100722055602.GA18566@infradead.org> <20100722140044.GA28684@redhat.com> <20100724085135.GB32006@infradead.org> <20100726143300.GG12449@redhat.com> Date: Thu, 29 Jul 2010 21:57:43 +0200 Message-ID: Subject: Re: [RFC PATCH] cfq-iosced: Implement IOPS mode and group_idle tunable V3 From: Corrado Zoccolo To: Vivek Goyal Cc: Christoph Hellwig , linux-kernel@vger.kernel.org, axboe@kernel.dk, nauman@google.com, dpshah@google.com, guijianfeng@cn.fujitsu.com, jmoyer@redhat.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2144 Lines: 47 On Mon, Jul 26, 2010 at 4:33 PM, Vivek Goyal wrote: > On Sat, Jul 24, 2010 at 11:07:07AM +0200, Corrado Zoccolo wrote: >> On Sat, Jul 24, 2010 at 10:51 AM, Christoph Hellwig wrote: >> > To me this sounds like slice_idle=0 is the right default then, as it >> > gives useful behaviour for all systems linux runs on. >> No, it will give bad performance on single disks, possibly worse than >> deadline (deadline at least sorts the requests between different >> queues, while CFQ with slice_idle=0 doesn't even do this for readers). > > Not sure if CFQ will be worse than deadline with slice_idle=0. CFQ has > some inbuilt things which should help. > > - Readers preempt Writers > - All writers go in one single queue (at one prio level), readers get >  their individual queues and can outnumber writers. > > So I guess CFQ with slice_idle=0 should not be worse than deadline in terms > of read latencies. I was thinking more to the fact that read requests are not sorted: they will basically be serviced in FIFO order, while deadline will sort them and possibly increase locality. In the reader vs writer case, cfq may have a small edge. Basically, they will severely underperform vs. cfq with slice != 0, though. > > Vivek > -- __________________________________________________________________________ dott. Corrado Zoccolo                          mailto:czoccolo@gmail.com PhD - Department of Computer Science - University of Pisa, Italy -------------------------------------------------------------------------- The self-confidence of a warrior is not the self-confidence of the average man. The average man seeks certainty in the eyes of the onlooker and calls that self-confidence. The warrior seeks impeccability in his own eyes and calls that humbleness.                                Tales of Power - C. Castaneda -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/