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    SubjectRe: [PATCH v3 1/3] sched/fair: add util_est on top of PELT
    On Tue, Jan 23, 2018 at 10:08 AM, Patrick Bellasi
    <patrick.bellasi@arm.com> wrote:
    > The util_avg signal computed by PELT is too variable for some use-cases.
    > For example, a big task waking up after a long sleep period will have its
    > utilization almost completely decayed. This introduces some latency before
    > schedutil will be able to pick the best frequency to run a task.
    [...]
    > -static inline unsigned long task_util(struct task_struct *p);
    > static unsigned long cpu_util_wake(int cpu, struct task_struct *p);
    >
    > static unsigned long capacity_spare_wake(int cpu, struct task_struct *p)
    > @@ -6262,6 +6337,11 @@ static inline unsigned long task_util(struct task_struct *p)
    > return p->se.avg.util_avg;
    > }
    >
    > +static inline unsigned long task_util_est(struct task_struct *p)
    > +{
    > + return max(p->se.avg.util_est.ewma, p->se.avg.util_est.last);
    > +}
    > +
    > /*
    > * cpu_util_wake: Compute cpu utilization with any contributions from
    > * the waking task p removed.
    > diff --git a/kernel/sched/features.h b/kernel/sched/features.h
    > index 9552fd5854bf..c459a4b61544 100644
    > --- a/kernel/sched/features.h
    > +++ b/kernel/sched/features.h
    > @@ -85,3 +85,8 @@ SCHED_FEAT(ATTACH_AGE_LOAD, true)
    > SCHED_FEAT(WA_IDLE, true)
    > SCHED_FEAT(WA_WEIGHT, true)
    > SCHED_FEAT(WA_BIAS, true)
    > +
    > +/*
    > + * UtilEstimation. Use estimated CPU utilization.
    > + */
    > +SCHED_FEAT(UTIL_EST, false)
    > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
    > index 2e95505e23c6..0b4d9750a927 100644
    > --- a/kernel/sched/sched.h
    > +++ b/kernel/sched/sched.h
    > @@ -470,6 +470,7 @@ struct cfs_rq {
    > * CFS load tracking
    > */
    > struct sched_avg avg;
    > + unsigned long util_est_runnable;

    Since struct sched_avg would now have util_est, cfs_rq gets it too.
    Then can we not try to reuse that struct and avoid having to expand
    cfs_rq more than needed?

    I went through previous conversations and couldn't find a reason, if I
    missed something I appreciate if you can explain the rationale.

    thanks,

    - Joel

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