From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756269AbZJCNVN (ORCPT ); Sat, 3 Oct 2009 09:21:13 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755884AbZJCNVM (ORCPT ); Sat, 3 Oct 2009 09:21:12 -0400 Received: from brick.kernel.dk ([93.163.65.50]:43608 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755858AbZJCNVM (ORCPT ); Sat, 3 Oct 2009 09:21:12 -0400 Date: Sat, 3 Oct 2009 15:21:15 +0200 From: Jens Axboe To: Vivek Goyal Cc: Mike Galbraith , Ingo Molnar , Linus Torvalds , 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: Do not overload dispatch queue (Was: Re: IO scheduler based IO controller V10) Message-ID: <20091003132115.GB31616@kernel.dk> References: <20091002172046.GA2376@elte.hu> <20091002172554.GJ31616@kernel.dk> <20091002172842.GA4884@elte.hu> <20091002173732.GK31616@kernel.dk> <1254507215.8667.7.camel@marge.simson.net> <20091002181903.GN31616@kernel.dk> <1254548931.8299.18.camel@marge.simson.net> <1254549378.8299.21.camel@marge.simson.net> <20091003112915.GA12925@redhat.com> <20091003124049.GB12925@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20091003124049.GB12925@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Oct 03 2009, Vivek Goyal wrote: > On Sat, Oct 03, 2009 at 07:29:15AM -0400, Vivek Goyal wrote: > > On Sat, Oct 03, 2009 at 07:56:18AM +0200, Mike Galbraith wrote: > > > On Sat, 2009-10-03 at 07:49 +0200, Mike Galbraith wrote: > > > > On Fri, 2009-10-02 at 20:19 +0200, Jens Axboe wrote: > > > > > > > > > If you could do a cleaned up version of your overload patch based on > > > > > this: > > > > > > > > > > http://git.kernel.dk/?p=linux-2.6-block.git;a=commit;h=1d2235152dc745c6d94bedb550fea84cffdbf768 > > > > > > > > > > then lets take it from there. > > > > > > > > Note to self: build the darn thing after last minute changes. > > > > > > Block: Delay overloading of CFQ queues to improve read latency. > > > > > > Introduce a delay maximum dispatch timestamp, and stamp it when: > > > 1. we encounter a known seeky or possibly new sync IO queue. > > > 2. the current queue may go idle and we're draining async IO. > > > 3. we have sync IO in flight and are servicing an async queue. > > > 4 we are not the sole user of disk. > > > Disallow exceeding quantum if any of these events have occurred recently. > > > > > > > So it looks like primarily the issue seems to be that we done lot of > > dispatch from async queue and if some sync queue comes in now, it will > > experience latencies. > > > > For a ongoing seeky sync queue issue will be solved up to some extent > > because previously we did not choose to idle for that queue now we will > > idle, hence async queue will not get a chance to overload the dispatch > > queue. > > > > For the sync queues where we choose not to enable idle, we still will see > > the latencies. Instead of time stamping on all the above events, can we > > just keep track of last sync request completed in the system and don't > > allow async queue to flood/overload the dispatch queue with-in certain > > time limit of that last sync request completion. This just gives a buffer > > period to that sync queue to come back and submit more requests and > > still not suffer large latencies? > > > > Thanks > > Vivek > > > > Hi Mike, > > Following is a quick hack patch for the above idea. It is just compile and > boot tested. Can you please see if it helps in your scenario. > > Thanks > Vivek > > > o Do not allow more than max_dispatch requests from an async queue, if some > sync request has finished recently. This is in the hope that sync activity > is still going on in the system and we might receive a sync request soon. > Most likely from a sync queue which finished a request and we did not enable > idling on it. This is pretty much identical to the scheme I described, except for the ramping of queue depth. I've applied it, it's nice and simple and I believe this will get rid of the worst of the problem. Things probably end up being a bit simplistic, but we can always tweak around later. -- Jens Axboe