Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755992AbZJBWOZ (ORCPT ); Fri, 2 Oct 2009 18:14:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755703AbZJBWOZ (ORCPT ); Fri, 2 Oct 2009 18:14:25 -0400 Received: from mail-yw0-f176.google.com ([209.85.211.176]:39461 "EHLO mail-yw0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755588AbZJBWOY convert rfc822-to-8bit (ORCPT ); Fri, 2 Oct 2009 18:14:24 -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=p8Q+V8F5rFLOqvh3oakiE+Ho6RE/tzhM7ob39dYJeZTFlZL0J1Ht6yglu4XiIYABUj i7PZ2eV/W2Dvq78a0K4TSSLd6DmOBCas9rS37H+TuPgXQ0G65/q3It1hMhEdydWz9PAC oa+8r8ohI3/3UgfDAXqdKYUyei6sLaft+txp0= MIME-Version: 1.0 In-Reply-To: <20091002195815.GE4494@redhat.com> References: <200910021255.27689.czoccolo@gmail.com> <20091002124921.GA4494@redhat.com> <4e5e476b0910020827s23e827b1n847c64e355999d4a@mail.gmail.com> <1254497520.10392.11.camel@marge.simson.net> <20091002154020.GC4494@redhat.com> <12774.1254502217@turing-police.cc.vt.edu> <20091002195815.GE4494@redhat.com> Date: Sat, 3 Oct 2009 00:14:28 +0200 Message-ID: <4e5e476b0910021514i1b461229t667bed94fd67f140@mail.gmail.com> Subject: Re: IO scheduler based IO controller V10 From: Corrado Zoccolo To: Vivek Goyal Cc: Valdis.Kletnieks@vt.edu, Mike Galbraith , Jens Axboe , Ingo Molnar , Ulrich Lukas , linux-kernel@vger.kernel.org, containers@lists.linux-foundation.org, dm-devel@redhat.com, nauman@google.com, dpshah@google.com, lizf@cn.fujitsu.com, mikew@google.com, fchecconi@gmail.com, paolo.valente@unimore.it, ryov@valinux.co.jp, fernando@oss.ntt.co.jp, jmoyer@redhat.com, dhaval@linux.vnet.ibm.com, balbir@linux.vnet.ibm.com, righi.andrea@gmail.com, m-ikeda@ds.jp.nec.com, agk@redhat.com, akpm@linux-foundation.org, peterz@infradead.org, jmarchan@redhat.com, torvalds@linux-foundation.org, riel@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: 2282 Lines: 53 On Fri, Oct 2, 2009 at 9:58 PM, Vivek Goyal wrote: > On Fri, Oct 02, 2009 at 12:50:17PM -0400, Valdis.Kletnieks@vt.edu wrote: >> On Fri, 02 Oct 2009 11:40:20 EDT, Vivek Goyal said: >> >> Umm... I got petabytes of hardware RAID across the hall that very definitely >> *is* rotating.  Did you mean "SSD and disk systems with big honking caches >> that cover up the rotation"?  Because "RAID" and "big honking caches" are >> not *quite* the same thing, and I can just see that corner case coming out >> to bite somebody on the ass... >> > > I guess both. The systems which have big caches and cover up for rotation, > we probably need not idle for seeky process. An in case of big hardware > RAID, having multiple rotating disks, instead of idling and keeping rest > of the disks free, we probably are better off dispatching requests from > next queue (hoping it is going to a different disk altogether). In fact I think that the 'rotating' flag name is misleading. All the checks we are doing are actually checking if the device truly supports multiple parallel operations, and this feature is shared by hardware raids and NCQ enabled SSDs, but not by cheap SSDs or single NCQ-enabled SATA disk. If we really wanted a "seek is cheap" flag, we could measure seek time in the io-scheduler itself, but in the current code base we don't have it used in this meaning anywhere. Thanks, Corrado > > Thanks > 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/