From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757012Ab2FTQIE (ORCPT ); Wed, 20 Jun 2012 12:08:04 -0400 Received: from e28smtp08.in.ibm.com ([122.248.162.8]:54243 "EHLO e28smtp08.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756951Ab2FTQIB (ORCPT ); Wed, 20 Jun 2012 12:08:01 -0400 Message-ID: <4FE1F4FD.3050101@linux.vnet.ibm.com> Date: Wed, 20 Jun 2012 21:36:21 +0530 From: "Srivatsa S. Bhat" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:12.0) Gecko/20120424 Thunderbird/12.0 MIME-Version: 1.0 To: Ingo Molnar CC: Peter Zijlstra , pjt@google.com, paul@paulmenage.org, akpm@linux-foundation.org, rjw@sisk.pl, nacc@us.ibm.com, rientjes@google.com, paulmck@linux.vnet.ibm.com, tglx@linutronix.de, seto.hidetoshi@jp.fujitsu.com, tj@kernel.org, mschmidt@redhat.com, berrange@redhat.com, nikunj@linux.vnet.ibm.com, vatsa@linux.vnet.ibm.com, liuj97@gmail.com, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org Subject: Re: [PATCH v6 0/4] CPU hotplug, cpusets, suspend/resume: Fixes, cleanups and optimizations References: <20120524141510.3692.64549.stgit@srivatsabhat.in.ibm.com> <4FE199B6.2050803@linux.vnet.ibm.com> <20120620113917.GA1925@gmail.com> <4FE1DB88.9060405@linux.vnet.ibm.com> <20120620144735.GA2007@gmail.com> In-Reply-To: <20120620144735.GA2007@gmail.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit x-cbid: 12062016-2000-0000-0000-000007FBDF29 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/20/2012 08:17 PM, Ingo Molnar wrote: > > * Srivatsa S. Bhat wrote: > >> On 06/20/2012 05:09 PM, Ingo Molnar wrote: >> >>> * Srivatsa S. Bhat wrote: >>> >>>> On 05/24/2012 07:46 PM, Srivatsa S. Bhat wrote: >>>> >>>>> Currently the kernel doesn't handle cpusets properly during >>>>> suspend/resume. After a resume, all non-root cpusets end up >>>>> having only 1 cpu (the boot cpu), causing massive >>>>> performance degradation of workloads. One major user of >>>>> cpusets is libvirt, which means that after a >>>>> suspend/hibernation cycle, all VMs suddenly end up running >>>>> terribly slow! >>>>> >>>>> Also, the kernel moves the tasks from one cpuset to another >>>>> during CPU hotplug in the suspend/resume path, leading to a >>>>> task-management nightmare after resume. >>>>> >>>>> Patch 1 fixes this by keeping cpusets unmodified in the >>>>> suspend/resume path. But to ensure we don't trip over, it >>>>> keeps the sched domains updated during every CPU hotplug in >>>>> the s/r path. This is a long standing issue and we need to >>>>> fix up stable kernels too. >>>>> >>>>> The rest of the patches in the series are mostly >>>>> cleanups/optimizations. >>>> >>>> Hi Peter, >>>> >>>> Would you be taking these patches through -tip for 3.6? >>> >>> They are now in tip:sched/core. >>> >>> Note that I removed the Cc:stable tag - it's not a regression >>> fix and such it is not eligible for immediate -stable backports. >>> >>> ( Once they are upstream and have been problem-free upstream for >>> several weeks then *maybe* we could forward the first commit >>> to -stable, as a super special exception. ) >>> >> >> >> OK, I get the point of allowing it to cook in the mainline for >> a while before backporting to -stable and I totally agree with >> that, but why so much of uncertainty about whether the first >> commit should (eventually) even land in -stable or not? >> Distros have been struggling to deal with this bug in >> userspace and have failed, and AFAIK they are waiting for a >> proper kernel fix for this bug. Agreed, this is not a >> regression per se, but isn't this bug critical enough to >> qualify for -stable? > > No, as a general rule only regression fixes are included in > -stable. The workflow is this: in the v3.4 -stable kernel we > included fixes that were introduced in the v3.4 merge window, > i.e. bugs that were introduced after v3.3 was released. > > Not 'fixes' in general. > > Fixes for "has been broken forever" problems (like this one) go > upstream and get released in the next stable kernel that gets > released - v3.6 in this case. > Ah, ok.. Thanks for the explanation! Regards, Srivatsa S. Bhat