linux-kernel - Re: [PATCH v5 0/5] CPU hotplug, cpusets, suspend/resume: Fixes, cleanups and optimizations

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Date:	Sun, 20 May 2012 19:28:03 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	mingo@...nel.org, 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 v5 0/5] CPU hotplug, cpusets, suspend/resume: Fixes, cleanups
 and optimizations

Hi Peter,

Did you get a chance to take a look at this patchset?

(I have added a summary of the changes between the versions below.)

Thanks a lot!

On 05/17/2012 10:29 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
> (except patch 4 which is a non-critical bug fix).
>


Changelog:

v5 : Don't do explicit save/restore of cpusets' cpu masks during s/r, to avoid
     the overhead of a new per-cpuset cpu mask to help with that. Also, ensure
     that the sched domains are updated on each hotplug.
     The s/r fix (patch 1) is now distinct from the cleanups (patches 2-5).

v4 : (Never had this version. I skipped from v3 to v5 accidentally).

v3 : Explicitly save and restore cpusets' cpu masks during s/r. Don't alter
     the semantics of regular cpu hotplug.
     http://thread.gmane.org/gmane.linux.kernel/1296339

v2 : http://thread.gmane.org/gmane.linux.documentation/4805/

v1 : thread.gmane.org/gmane.linux.kernel/1250097/
 

> --
>  Srivatsa S. Bhat (5):
>       CPU hotplug, cpusets, suspend: Don't modify cpusets during suspend/resume
>       cpusets, hotplug: Implement cpuset tree traversal in a helper function
>       cpusets, hotplug: Restructure functions that are invoked during hotplug
>       cpusets: Update tasks' cpus_allowed mask upon updates to root cpuset
>       cpusets: Remove/update outdated comments
> 
> 
>   include/linux/cpuset.h |    4 +
>  kernel/cpuset.c        |  161 +++++++++++++++++++++++++++++++++++-------------
>  kernel/sched/core.c    |   44 +++++++++++--
>  3 files changed, 159 insertions(+), 50 deletions(-)


Regards,
Srivatsa S. Bhat

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