Re: [PATCH 1/6] cpufreq: Reduce cpufreq_update_util() overhead a bit

Viresh Kumar
2016-03-03T05:48:38Z

On 02-03-16, 03:04, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> 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>
> ---
>
> Supersedes https://patchwork.kernel.org/patch/8443191/

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>

--
viresh