Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752453Ab1CKQjp (ORCPT ); Fri, 11 Mar 2011 11:39:45 -0500 Received: from mx1.redhat.com ([209.132.183.28]:56078 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751298Ab1CKQjo (ORCPT ); Fri, 11 Mar 2011 11:39:44 -0500 Date: Fri, 11 Mar 2011 11:39:27 -0500 From: Vivek Goyal To: Justin TerAvest Cc: m-ikeda@ds.jp.nec.com, jaxboe@fusionio.com, linux-kernel@vger.kernel.org, ryov@valinux.co.jp, taka@valinux.co.jp, kamezawa.hiroyu@jp.fujitsu.com, righi.andrea@gmail.com, guijianfeng@cn.fujitsu.com, balbir@linux.vnet.ibm.com, ctalbott@google.com, nauman@google.com, mrubin@google.com Subject: Re: [RFC] [PATCH 0/6] Provide cgroup isolation for buffered writes. Message-ID: <20110311163927.GA4104@redhat.com> References: <1299619256-12661-1-git-send-email-teravest@google.com> <20110308224325.GK27455@redhat.com> <20110308225059.GL27455@redhat.com> <20110311024732.GB11710@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4192 Lines: 103 On Fri, Mar 11, 2011 at 08:07:17AM -0800, Justin TerAvest wrote: > On Thu, Mar 10, 2011 at 6:47 PM, Vivek Goyal wrote: > > On Wed, Mar 09, 2011 at 10:04:11AM -0800, Justin TerAvest wrote: > >> On Tue, Mar 8, 2011 at 2:50 PM, Vivek Goyal wrote: > >> > On Tue, Mar 08, 2011 at 05:43:25PM -0500, Vivek Goyal wrote: > >> >> On Tue, Mar 08, 2011 at 01:20:50PM -0800, Justin TerAvest wrote: > >> >> > This patchset adds tracking to the page_cgroup structure for which cgroup has > >> >> > dirtied a page, and uses that information to provide isolation between > >> >> > cgroups performing writeback. > >> >> > > >> >> > >> >> Justin, > >> >> > >> >> So if somebody is trying to isolate a workload which does bunch of READS > >> >> and lots of buffered WRITES, this patchset should help in the sense that > >> >> all the heavy WRITES can be put into a separate cgroup of low weight? > >> >> > >> >> Other application which are primarily doing READS, direct WRITES or little > >> >> bit of buffered WRITES should still get good latencies if heavy writer > >> >> is isolated in a separate group? > >> >> > >> >> If yes, then this piece standalone can make sense. And once the other > >> >> piece/patches of memory cgroup dirty ratio and cgroup aware buffered > >> >> writeout come in, then one will be able to differentiate buffered writes > >> >> of different groups. > >> > > >> > Thinking more about it, currently anyway SYNC preempts the ASYNC. So the > >> > question would be will it help me enable get better isolation latencies > >> > of READS agains buffered WRITES? > >> > >> Ah! Sorry, I left out a patch that disables cross-group preemption. > >> I'll add that to the patchset and email out v2 soon. > > > > Well, what I was referring to that even in current code sync preempts > > all async in CFQ. So it looks like this patchset will not help get > > better latencies in presence of WRITES? > > Hi Vivek, > > I should have been more clear. I forgot to include a patch that > changes the behavior of that preemption. I haven't mailed out v2 yet > because I was also writing a change to put the css_id in pc->flags > instead of its own field. > > The preemption change would look like: > > Previously, a sync queue in can preempt an async queue in another > cgroup. This changes that behavior to disallow such preemption. > > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c > index ab7a216..0494c0c 100644 > --- a/block/cfq-iosched.c > +++ b/block/cfq-iosched.c > @@ -3390,6 +3390,9 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue > if (!cfqq) > return false; > > + if (new_cfqq->cfqg != cfqq->cfqg) > + return false; > + > if (cfq_class_idle(new_cfqq)) > return false; > > @@ -3409,9 +3412,6 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue > if (rq_is_sync(rq) && !cfq_cfqq_sync(cfqq)) > return true; > > - if (new_cfqq->cfqg != cfqq->cfqg) > - return false; > > I will include the test results that show that isolation is also > improved between a reader and a buffered writer. > Justin, Right now all the async queues go in one cgroup and that is root cgroup. So it is perfectly fine to let sync preempt async. I will be interested in seeing the results. But do you have a theoritical explanation also that why with this patch set we will get better isolation between READS and WRITES? Especially after following patch from Shaohua Li. commit f8ae6e3eb8251be32c6e913393d9f8d9e0609489 Author: Shaohua Li Date: Fri Jan 14 08:41:02 2011 +0100 block cfq: make queue preempt work for queues from different workload This patch will make sure that sync always preempt async. So I am not able to understand that how this patch series provides better latencies for READS in presence of WRITES. Thanks Vivek -- 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/