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    SubjectRe: [PATCH] sched/fair: remove redundant call to cpufreq_update_util
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    On Wednesday, January 15, 2020 11:20:20 AM CET Vincent Guittot wrote:
    > With commit bef69dd87828 ("sched/cpufreq: Move the cfs_rq_util_change() call to cpufreq_update_util()")
    > update_load_avg() has become the central point for calling cpufreq (not
    > including the update of blocked load). This change helps to simplify
    > further the number of call to cpufreq_update_util() and to remove last

    s/call/calls/

    And the patch looks reasonable to me.

    > redundant ones. With update_load_avg(), we are now sure that
    > cpufreq_update_util() will be called after every task attachment to a
    > cfs_rq and especially after propagating this event down to the util_avg of
    > the root cfs_rq, which is the level that is used by cpufreq governors like
    > schedutil to set the frequency of a CPU.
    >
    > The SCHED_CPUFREQ_MIGRATION flag forces an early call to cpufreq when the
    > migration happens in a cgroup whereas util_avg of root cfs_rq is not yet
    > updated and this call is duplicated with the one that happens immediately
    > after when the migration event reaches the root cfs_rq. The dedicated flag
    > SCHED_CPUFREQ_MIGRATION is now useless and can be removed. The interface of
    > attach_entity_load_avg() can also be simplified accordingly.
    >
    > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>

    Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

    > ---
    > include/linux/sched/cpufreq.h | 1 -
    > kernel/sched/fair.c | 14 +++++++-------
    > 2 files changed, 7 insertions(+), 8 deletions(-)
    >
    > diff --git a/include/linux/sched/cpufreq.h b/include/linux/sched/cpufreq.h
    > index cc6bcc1e96bc..3ed5aa18593f 100644
    > --- a/include/linux/sched/cpufreq.h
    > +++ b/include/linux/sched/cpufreq.h
    > @@ -9,7 +9,6 @@
    > */
    >
    > #define SCHED_CPUFREQ_IOWAIT (1U << 0)
    > -#define SCHED_CPUFREQ_MIGRATION (1U << 1)
    >
    > #ifdef CONFIG_CPU_FREQ
    > struct cpufreq_policy;
    > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    > index 2d170b5da0e3..023aa42aaac7 100644
    > --- a/kernel/sched/fair.c
    > +++ b/kernel/sched/fair.c
    > @@ -801,7 +801,7 @@ void post_init_entity_util_avg(struct task_struct *p)
    > * For !fair tasks do:
    > *
    > update_cfs_rq_load_avg(now, cfs_rq);
    > - attach_entity_load_avg(cfs_rq, se, 0);
    > + attach_entity_load_avg(cfs_rq, se);
    > switched_from_fair(rq, p);
    > *
    > * such that the next switched_to_fair() has the
    > @@ -3114,7 +3114,7 @@ static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq, int flags)
    > {
    > struct rq *rq = rq_of(cfs_rq);
    >
    > - if (&rq->cfs == cfs_rq || (flags & SCHED_CPUFREQ_MIGRATION)) {
    > + if (&rq->cfs == cfs_rq) {
    > /*
    > * There are a few boundary cases this might miss but it should
    > * get called often enough that that should (hopefully) not be
    > @@ -3520,7 +3520,7 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
    > * Must call update_cfs_rq_load_avg() before this, since we rely on
    > * cfs_rq->avg.last_update_time being current.
    > */
    > -static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
    > +static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
    > {
    > u32 divider = LOAD_AVG_MAX - 1024 + cfs_rq->avg.period_contrib;
    >
    > @@ -3556,7 +3556,7 @@ static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
    >
    > add_tg_cfs_propagate(cfs_rq, se->avg.load_sum);
    >
    > - cfs_rq_util_change(cfs_rq, flags);
    > + cfs_rq_util_change(cfs_rq, 0);
    >
    > trace_pelt_cfs_tp(cfs_rq);
    > }
    > @@ -3614,7 +3614,7 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
    > *
    > * IOW we're enqueueing a task on a new CPU.
    > */
    > - attach_entity_load_avg(cfs_rq, se, SCHED_CPUFREQ_MIGRATION);
    > + attach_entity_load_avg(cfs_rq, se);
    > update_tg_load_avg(cfs_rq, 0);
    >
    > } else if (decayed) {
    > @@ -3871,7 +3871,7 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
    > static inline void remove_entity_load_avg(struct sched_entity *se) {}
    >
    > static inline void
    > -attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) {}
    > +attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}
    > static inline void
    > detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}
    >
    > @@ -10439,7 +10439,7 @@ static void attach_entity_cfs_rq(struct sched_entity *se)
    >
    > /* Synchronize entity with its cfs_rq */
    > update_load_avg(cfs_rq, se, sched_feat(ATTACH_AGE_LOAD) ? 0 : SKIP_AGE_LOAD);
    > - attach_entity_load_avg(cfs_rq, se, 0);
    > + attach_entity_load_avg(cfs_rq, se);
    > update_tg_load_avg(cfs_rq, false);
    > propagate_entity_cfs_rq(se);
    > }
    >




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