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    SubjectRe: [PATCH v2 09/10] sched/fair: stop load tracking when task switched_from_fair()
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    On 13/07/2022 06:04, Chengming Zhou wrote:
    > The same reason as the previous commit, if we don't reset the
    > sched_avg last_update_time to 0, after a while in switched_to_fair():
    >
    > switched_to_fair
    > attach_task_cfs_rq
    > attach_entity_cfs_rq
    > update_load_avg
    > __update_load_avg_se(now, cfs_rq, se)
    >
    > The delta (now - sa->last_update_time) will wrongly contribute/decay
    > sched_avg depends on the task running/runnable status at that time.

    IMHO, a queued !fair task when switching back to fair will already be
    enqueued (attached) as a fair task in __sched_setscheduler() prior to
    the check_class_changed() call.

    I can't see how this will work with your proposed change in using
    last_update_time=0 for fair->!fair->fair class changes?

    > This patch reset it's sched_avg last_update_time to 0, stop load
    > tracking for !fair task, later in switched_to_fair() ->
    > update_load_avg(), we can use its saved sched_avg.
    >
    > Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
    > ---
    > kernel/sched/fair.c | 5 +++++
    > 1 file changed, 5 insertions(+)
    >
    > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    > index 50f65a2ede32..576028f5a09e 100644
    > --- a/kernel/sched/fair.c
    > +++ b/kernel/sched/fair.c
    > @@ -11552,6 +11552,11 @@ static void attach_task_cfs_rq(struct task_struct *p)
    > static void switched_from_fair(struct rq *rq, struct task_struct *p)
    > {
    > detach_task_cfs_rq(p);
    > +
    > +#ifdef CONFIG_SMP
    > + /* Stop load tracking for !fair task */
    > + p->se.avg.last_update_time = 0;
    > +#endif
    > }
    >
    > static void switched_to_fair(struct rq *rq, struct task_struct *p)

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