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

["Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>]

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