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    SubjectRe: [RFC PATCH v4 4/6] sched/cpufreq: Introduce sugov_cpu_ramp_boost
    On Thu, Jan 23, 2020 at 6:21 PM Douglas Raillard
    <douglas.raillard@arm.com> wrote:
    >
    >
    >
    > On 1/23/20 3:55 PM, Rafael J. Wysocki wrote:
    > > On Wed, Jan 22, 2020 at 6:36 PM Douglas RAILLARD
    > > <douglas.raillard@arm.com> wrote:
    > >>
    > >> Use the utilization signals dynamic to detect when the utilization of a
    > >> set of tasks starts increasing because of a change in tasks' behavior.
    > >> This allows detecting when spending extra power for faster frequency
    > >> ramp up response would be beneficial to the reactivity of the system.
    > >>
    > >> This ramp boost is computed as the difference between util_avg and
    > >> util_est_enqueued. This number somehow represents a lower bound of how
    > >> much extra utilization this tasks is actually using, compared to our
    > >> best current stable knowledge of it (which is util_est_enqueued).
    > >>
    > >> When the set of runnable tasks changes, the boost is disabled as the
    > >> impact of blocked utilization on util_avg will make the delta with
    > >> util_est_enqueued not very informative.
    > >>
    > >> Signed-off-by: Douglas RAILLARD <douglas.raillard@arm.com>
    > >> ---
    > >> kernel/sched/cpufreq_schedutil.c | 43 ++++++++++++++++++++++++++++++++
    > >> 1 file changed, 43 insertions(+)
    > >>
    > >> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
    > >> index 608963da4916..25a410a1ff6a 100644
    > >> --- a/kernel/sched/cpufreq_schedutil.c
    > >> +++ b/kernel/sched/cpufreq_schedutil.c
    > >> @@ -61,6 +61,10 @@ struct sugov_cpu {
    > >> unsigned long bw_dl;
    > >> unsigned long max;
    > >>
    > >> + unsigned long ramp_boost;
    > >> + unsigned long util_est_enqueued;
    > >> + unsigned long util_avg;
    > >> +
    > >> /* The field below is for single-CPU policies only: */
    > >> #ifdef CONFIG_NO_HZ_COMMON
    > >> unsigned long saved_idle_calls;
    > >> @@ -183,6 +187,42 @@ static void sugov_deferred_update(struct sugov_policy *sg_policy, u64 time,
    > >> }
    > >> }
    > >>
    > >> +static unsigned long sugov_cpu_ramp_boost(struct sugov_cpu *sg_cpu)
    > >> +{
    > >> + return READ_ONCE(sg_cpu->ramp_boost);
    > >> +}
    > >
    > > Where exactly is this function used?
    >
    > In the next commit where the boost value is actually used to do
    > something. The function is introduced here to keep the
    > WRITE_ONCE/READ_ONCE pair together.

    But ramp_boost itself is not really used in this patch too AFAICS.

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