[PATCH V5 0/2] sched: cpufreq: Allow remote callbacks

[Viresh Kumar]

With Android UI and benchmarks the latency of cpufreq response to
certain scheduling events can become very critical. Currently, callbacks
into cpufreq governors are only made from the scheduler if the target
CPU of the event is the same as the current CPU. This means there are
certain situations where a target CPU may not run the cpufreq governor
for some time.

One testcase [1] to show this behavior is where a task starts running on
CPU0, then a new task is also spawned on CPU0 by a task on CPU1. If the
system is configured such that the new tasks should receive maximum
demand initially, this should result in CPU0 increasing frequency
immediately. But because of the above mentioned limitation though, this
does not occur.

This series updates the scheduler core to call the cpufreq callbacks for
remote CPUs as well and updates the registered hooks to handle that.

This is tested with couple of usecases (Android: hackbench, recentfling,
galleryfling, vellamo, Ubuntu: hackbench) on ARM hikey board (64 bit
octa-core, single policy). Only galleryfling showed minor improvements,
while others didn't had much deviation.

The reason being that this patch only targets a corner case, where
following are required to be true to improve performance and that
doesn't happen too often with these tests:

- Task is migrated to another CPU.
- The task has high demand, and should take the target CPU to higher
  OPPs.
- And the target CPU doesn't call into the cpufreq governor until the
  next tick.

Rebased over: pm/linux-next

V4->V5:
- Drop cpu field from "struct update_util_data" and add it in "struct
  sugov_cpu" instead.
- Can't have separate patches now because of the above change and so
  merged all the patches from V4 into a single patch.
- Add a comment suggested by PeterZ.
- Commit log of 1/2 is improved to contain more details.
- A new patch (which was posted during V1) is also added to take care of
  platforms where any CPU can do DVFS on behalf of any other CPU, even
  if they are part of different cpufreq policies. This has been
  requested by Saravana several times already and as the series is quite
  straight forward now, I decided to include it in.

V3->V4:
- Respect iowait boost flag and util updates for the all remote
  callbacks.
- Minor updates in commit log of 2/3.

V2->V3:
- Rearranged/merged patches as suggested by Rafael (looks much better
  now)
- Also handle new hook added to intel-pstate driver.
- The final code remains the same as V2, except for the above hook.

V1->V2:
- Don't support remote callbacks for unshared cpufreq policies.
- Don't support remote callbacks where local CPU isn't part of the
  target CPU's cpufreq policy.
- Dropped dvfs_possible_from_any_cpu flag.

--
viresh

[1] http://pastebin.com/7LkMSRxE

Viresh Kumar (2):
  sched: cpufreq: Allow remote cpufreq callbacks
  cpufreq: Process remote callbacks from any CPU if the platform permits

 drivers/cpufreq/cpufreq-dt.c       |  1 +
 drivers/cpufreq/cpufreq_governor.c |  3 +++
 drivers/cpufreq/intel_pstate.c     |  8 ++++++++
 include/linux/cpufreq.h            | 23 +++++++++++++++++++++++
 kernel/sched/cpufreq_schedutil.c   | 31 ++++++++++++++++++++++++++-----
 kernel/sched/deadline.c            |  2 +-
 kernel/sched/fair.c                |  8 +++++---
 kernel/sched/rt.c                  |  2 +-
 kernel/sched/sched.h               | 10 ++--------
 9 files changed, 70 insertions(+), 18 deletions(-)

-- 
2.13.0.71.gd7076ec9c9cb