Messages in this thread | | | Date | Thu, 14 Jul 2022 14:33:21 +0200 | Subject | Re: [PATCH v2 09/10] sched/fair: stop load tracking when task switched_from_fair() | From | Dietmar Eggemann <> |
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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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