linux-kernel - [PATCH v3 0/5] CPU hotplug, cpusets: Fix issues with cpusets handling during suspend/resume

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Date:	Mon, 14 May 2012 04:44:31 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	a.p.zijlstra@...llo.nl, mingo@...nel.org, pjt@...gle.com,
	paul@...lmenage.org, akpm@...ux-foundation.org
Cc:	rjw@...k.pl, nacc@...ibm.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, srivatsa.bhat@...ux.vnet.ibm.com
Subject: [PATCH v3 0/5] CPU hotplug,
 cpusets: Fix issues with cpusets handling during suspend/resume

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.

This patchset solves these problems by reworking the way cpusets are handled
during CPU hotplug in the suspend/resume path. This doesn't involve any
change in semantics as to how cpusets are handled during regular CPU hotplug
because it is correct as it is.

Patches 1 & 2 are cleanups that separate out hotplug handling so that we can
implement different logic for different hotplug events (CPU/Mem
online/offline). This also leads to some optimizations and more importantly
prepares the ground for any further work dealing with cpusets during hotplug.

Patch 3 is a bug fix - it ensures that the tasks attached to the root cpuset
see the updated cpus_allowed mask upon CPU hotplug.

Patches 4 and 5 implement the fix for cpusets handling during suspend/resume.

--
 Srivatsa S. Bhat (5):
      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: Add provisions for distinguishing CPU Hotplug in suspend/resume path
      cpusets, suspend: Save and restore cpusets during suspend/resume

  include/linux/cpuset.h |    4 -
 kernel/cpuset.c        |  235 +++++++++++++++++++++++++++++++++++++++---------
 kernel/sched/core.c    |   29 +++++-
 3 files changed, 218 insertions(+), 50 deletions(-)

Thanks,
Srivatsa S. Bhat
IBM Linux Technology Center

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