[PATCH v5 0/2] Add cpu hotplug support for powerpc/perf/hv-24x7

[Kajol Jain]

This patchset add cpu hotplug support for hv_24x7 driver by adding
online/offline cpu hotplug function. It also add sysfs file
"cpumask" to expose current online cpu that can be used for
hv_24x7 event count.

Changelog:
v4 -> v5
- Since we are making PMU fail incase hotplug init failed, hence
  directly adding cpumask attr inside if_attrs rather then creating
  new attribute_group as suggested by Madhavan Srinivasan.

v3 -> v4
- Make PMU initialization fail incase hotplug init failed. Rather then
  just printing error msg.
- Did some nits changes like removing extra comment and initialising
  target value part as suggested by Michael Ellerman
- Retained Reviewd-by tag because the changes were fixes to some nits.

- Incase we sequentially offline multiple cpus, taking cpumask_first() may
  add some latency in that scenario.

  So, I was trying to test benchmark in power9 lpar with 16 cpu,
  by off-lining cpu 0-14

With cpumask_last: This is what I got.

real	0m2.812s
user	0m0.002s
sys	0m0.003s

With cpulast_any:
real	0m3.690s
user	0m0.002s
sys	0m0.062s

That's why I just went with cpumask_last thing.

v2 -> v3
- Corrected some of the typo mistakes and update commit message
  as suggested by Gautham R Shenoy.
- Added Reviewed-by tag for the first patch in the patchset.

v1 -> v2
- Changed function to pick active cpu incase of offline
  from "cpumask_any_but" to "cpumask_last", as
  cpumask_any_but function pick very next online cpu and incase where
  we are sequentially off-lining multiple cpus, "pmu_migrate_context"
  can add extra latency.
  - Suggested by: Gautham R Shenoy.

- Change documentation for cpumask and rather then hardcode the
  initialization for cpumask_attr_group, add loop to get very first
  NULL as suggested by Gautham R Shenoy.

Kajol Jain (2):
  powerpc/perf/hv-24x7: Add cpu hotplug support
  powerpc/hv-24x7: Add sysfs files inside hv-24x7 device to show cpumask

 .../sysfs-bus-event_source-devices-hv_24x7    |  7 +++
 arch/powerpc/perf/hv-24x7.c                   | 54 +++++++++++++++++++
 include/linux/cpuhotplug.h                    |  1 +
 3 files changed, 62 insertions(+)

-- 
2.26.2