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SubjectRe: [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@linux.vnet.ibm.com> wrote:
>
>> On 06/20/2012 05:09 PM, Ingo Molnar wrote:
>>
>>> * Srivatsa S. Bhat <srivatsa.bhat@linux.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



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