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Date: Wed, 20 Jun 2012 21:36:21 +0530 From: "Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com> To: Ingo Molnar <mingo@...nel.org> CC: Peter Zijlstra <a.p.zijlstra@...llo.nl>, pjt@...gle.com, paul@...lmenage.org, akpm@...ux-foundation.org, rjw@...k.pl, nacc@...ibm.com, rientjes@...gle.com, paulmck@...ux.vnet.ibm.com, tglx@...utronix.de, seto.hidetoshi@...fujitsu.com, tj@...nel.org, mschmidt@...hat.com, berrange@...hat.com, nikunj@...ux.vnet.ibm.com, vatsa@...ux.vnet.ibm.com, liuj97@...il.com, linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org Subject: Re: [PATCH v6 0/4] CPU hotplug, cpusets, suspend/resume: Fixes, cleanups and optimizations On 06/20/2012 08:17 PM, Ingo Molnar wrote: > > * Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com> wrote: > >> On 06/20/2012 05:09 PM, Ingo Molnar wrote: >> >>> * Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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