Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757556AbZJBRVZ (ORCPT ); Fri, 2 Oct 2009 13:21:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755559AbZJBRVY (ORCPT ); Fri, 2 Oct 2009 13:21:24 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:34735 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753769AbZJBRVX (ORCPT ); Fri, 2 Oct 2009 13:21:23 -0400 Date: Fri, 2 Oct 2009 19:20:46 +0200 From: Ingo Molnar To: Jens Axboe Cc: Linus Torvalds , Mike Galbraith , Vivek Goyal , 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, riel@redhat.com Subject: Re: IO scheduler based IO controller V10 Message-ID: <20091002172046.GA2376@elte.hu> References: <1254382405.7595.9.camel@marge.simson.net> <20091001185816.GU14918@kernel.dk> <1254464628.7158.101.camel@marge.simson.net> <20091002080417.GG14918@kernel.dk> <20091002092409.GA19529@elte.hu> <20091002092839.GA26962@kernel.dk> <20091002145610.GD31616@kernel.dk> <20091002171129.GG31616@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20091002171129.GG31616@kernel.dk> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1776 Lines: 38 * Jens Axboe wrote: > It's not _that_ easy, it depends a lot on the access patterns. A good > example of that is actually the idling that we already do. Say you > have two applications, each starting up. If you start them both at the > same time and just care for the dumb low latency, then you'll do one > IO from each of them in turn. Latency will be good, but throughput > will be aweful. And this means that in 20s they are both started, > while with the slice idling and priority disk access that CFQ does, > you'd hopefully have both up and running in 2s. > > So latency is good, definitely, but sometimes you have to worry about > the bigger picture too. Latency is more than single IOs, it's often > for complete operation which may involve lots of IOs. Single IO > latency is a benchmark thing, it's not a real life issue. And that's > where it becomes complex and not so black and white. Mike's test is a > really good example of that. To the extent of you arguing that Mike's test is artificial (i'm not sure you are arguing that) - Mike certainly did not do an artificial test - he tested 'konsole' cache-cold startup latency, such as: sh -c "perf stat -- konsole -e exit" 2>&1|tee -a $LOGFILE against a streaming dd. That is a _very_ relevant benchmark IMHO and konsole's cache footprint is far from trivial. (In fact i'd argue it's one of the most important IO benchmarks on a desktop system - how does your desktop hold up to something doing streaming IO.) Ingo -- 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/