cpufreq: Reduce cpufreq_update_util() overhead a bit
authorRafael J. Wysocki <rafael.j.wysocki@intel.com>
Fri, 4 Mar 2016 02:58:22 +0000 (03:58 +0100)
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>
Wed, 9 Mar 2016 14:07:58 +0000 (15:07 +0100)
commit08f511fd41c3afe303eb9b41bff0570f7c1b6937
tree719b4b878711f8c4312fccb9d479151a817fcbaf
parente6f036571e1f65021a442ec7aad087a6a239ecfb
cpufreq: Reduce cpufreq_update_util() overhead a bit

Use the observation that cpufreq_update_util() is only called
by the scheduler with rq->lock held, so the callers of
cpufreq_set_update_util_data() can use synchronize_sched()
instead of synchronize_rcu() to wait for cpufreq_update_util()
to complete.  Moreover, if they are updated to do that,
rcu_read_(un)lock() calls in cpufreq_update_util() might be
replaced with rcu_read_(un)lock_sched(), respectively, but
those aren't really necessary, because the scheduler calls
that function from RCU-sched read-side critical sections
already.

In addition to that, if cpufreq_set_update_util_data() checks
the func field in the struct update_util_data before setting
the per-CPU pointer to it, the data->func check may be dropped
from cpufreq_update_util() as well.

Make the above changes to reduce the overhead from
cpufreq_update_util() in the scheduler paths invoking it
and to make the cleanup after removing its callbacks less
heavy-weight somewhat.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
drivers/cpufreq/cpufreq.c
drivers/cpufreq/cpufreq_governor.c
drivers/cpufreq/intel_pstate.c