Re: [PATCH V2] cpufreq: schedutil: Redefine the rate_limit_us tunable

From: Rafael J. Wysocki
Date: Thu Feb 23 2017 - 18:37:13 EST


On Tue, Feb 21, 2017 at 5:45 AM, Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
> The rate_limit_us tunable is intended to reduce the possible overhead
> from running the schedutil governor. However, that overhead can be
> divided into two separate parts: the governor computations and the
> invocation of the scaling driver to set the CPU frequency. The latter
> is where the real overhead comes from. The former is much less
> expensive in terms of execution time and running it every time the
> governor callback is invoked by the scheduler, after rate_limit_us
> interval has passed since the last frequency update, would not be a
> problem.
>
> For this reason, redefine the rate_limit_us tunable so that it means the
> minimum time that has to pass between two consecutive invocations of the
> scaling driver by the schedutil governor (to set the CPU frequency).
>
> Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>

I'd prefer this to spend some time in linux-next before it goes into
the mainline, so I will queue it up for 4.12 if no one objects by the
end of the next week.

Thanks,
Rafael


> ---
> V1->V2: Update $subject and commit log (Rafael)
>
> kernel/sched/cpufreq_schedutil.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index fd4659313640..306d97e7b57c 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -92,14 +92,13 @@ static void sugov_update_commit(struct sugov_policy *sg_policy, u64 time,
> {
> struct cpufreq_policy *policy = sg_policy->policy;
>
> - sg_policy->last_freq_update_time = time;
> -
> if (policy->fast_switch_enabled) {
> if (sg_policy->next_freq == next_freq) {
> trace_cpu_frequency(policy->cur, smp_processor_id());
> return;
> }
> sg_policy->next_freq = next_freq;
> + sg_policy->last_freq_update_time = time;
> next_freq = cpufreq_driver_fast_switch(policy, next_freq);
> if (next_freq == CPUFREQ_ENTRY_INVALID)
> return;
> @@ -108,6 +107,7 @@ static void sugov_update_commit(struct sugov_policy *sg_policy, u64 time,
> trace_cpu_frequency(next_freq, smp_processor_id());
> } else if (sg_policy->next_freq != next_freq) {
> sg_policy->next_freq = next_freq;
> + sg_policy->last_freq_update_time = time;
> sg_policy->work_in_progress = true;
> irq_work_queue(&sg_policy->irq_work);
> }
> --
> 2.7.1.410.g6faf27b
>