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: NRafael J. Wysocki <rafael.j.wysocki@intel.com> Acked-by: NViresh Kumar <viresh.kumar@linaro.org> Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
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