Messages in this thread | | | Date | Sat, 16 Jul 2022 00:35:30 +0800 | Subject | Re: [External] Re: [PATCH v2 09/10] sched/fair: stop load tracking when task switched_from_fair() | From | Chengming Zhou <> |
| |
On 2022/7/15 19:15, Dietmar Eggemann wrote: > On 14/07/2022 15:43, Chengming Zhou wrote: >> On 2022/7/14 20:33, Dietmar Eggemann wrote: >>> On 13/07/2022 06:04, Chengming Zhou wrote: > > [...] > >>> 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. >> >> Right, this is true for a queued !fair task, it will enqueued (attached) before >> check_class_changed(). >> >> enqueue_task_fair() >> enqueue_entity() >> update_load_avg(cfs_rq, se, UPDATE_TG | DO_ATTACH) >> if (se->avg.last_update_time && !(flags & SKIP_AGE_LOAD)) --> true >> __update_load_avg_se(now, cfs_rq, se) --> (1) >> check_class_changed() >> switched_to_fair() >> attach_task_cfs_rq() >> attach_entity_cfs_rq() >> update_load_avg(cfs_rq, se, sched_feat(ATTACH_AGE_LOAD) ? 0 : SKIP_AGE_LOAD) >> if (se->avg.last_update_time && !(flags & SKIP_AGE_LOAD)) --> true >> __update_load_avg_se(now, cfs_rq, se) --> (2) >> >> >> 1. for queued !fair: (1) delta = (now - last_update_time), last_update_time is the time >> when switched_from_fair(). >> >> 2. for !queued !fair: (2) delta = (now - last_update_time), last_update_time is the time >> when switched_from_fair(). >> >> The scenario in the commit message only cover !queued !fair case, I forget the queued !fair >> case, their problem is the same. > > OK, that makes sense to me then. > >>> I can't see how this will work with your proposed change in using >>> last_update_time=0 for fair->!fair->fair class changes? >> If we reset last_update_time=0 for !fair task, then: >> >> 1. for queued !fair: will not do (1) since the if condition is false. >> >> 2. for !queued !fair: will not do (2) since the if condition is false. > OK. > > [...] > >>>> 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 */ > > You're not really stopping p->se load tracking by doing this. We don't > do this outside fair anyway. IMHO, you freeze p->se's PELT _avg/_sum > values to be used as initial values when re-entering fair. >
Yes, you are right, this comment is misleading and wrong, will delete it.
Thanks very much for your review!
>>>> + p->se.avg.last_update_time = 0; >>>> +#endif >>>> } >>>> >>>> static void switched_to_fair(struct rq *rq, struct task_struct *p) >
| |