Messages in this thread | | | Subject | Re: [PATCH] sched/pelt: sync util/runnable_sum with PELT window when propagating | From | Dietmar Eggemann <> | Date | Fri, 24 Apr 2020 14:07:35 +0200 |
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On 23/04/2020 18:17, Vincent Guittot wrote: > On Thu, 23 Apr 2020 at 16:30, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote: >> >> On 22/04/2020 17:14, Vincent Guittot wrote:
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>> gcfs --> tg --> gse >> ________________| >> | >> V >> >> cfs ---> tg (root) >> >> | >> V >> >> rq >> > > child cfs_rq aka gcfs_rq > | > gse: group entity that represents child cfs_rq in parent cfs_rq > | > v > parent cfs_rq aka cfs_rq
OK, I see. Maybe it's clearer to refer to child cfs_rq as gcfs_rq in this context.
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>>> /* Set new sched_entity's utilization */ >>> se->avg.util_avg = gcfs_rq->avg.util_avg; >>> - se->avg.util_sum = se->avg.util_avg * LOAD_AVG_MAX; >>> + se->avg.util_sum = se->avg.util_avg * divider; >> >> divider uses cfs_rq but we sync se->avg.util_avg with gcfs_rq here. > > we sync the util_avg of gse with the new util_avg of gcfs_rq but gse > is attached to cfs_rq and as a result we have to use cfs_rq's > period_contrib
I agree.
But the decay windows (avg.last_update_time, avg.period_contrib) of cfs_rq and gcfs_rq are not always aligned, I guess?
I see they are not after the online_fair_sched_group() -> attach_entity_cfs_rq() but later the are in sync as well.
I ran a couple of different rt-app taskgroup tests and try to
BUG_ON(se->avg.period_contrib != gcfs_rq->avg.period_contrib); BUG_ON(se->avg.last_update_time != gcfs_rq->avg.last_update_time)
in update_tg_cfs_util() but they didn't trigger so far.
Both, cfs_rq and gcfs_rq are in sync in update_tg_cfs_util() before and during a task runs in gcfs_rq.
Are there cases where this wouldn't necessary happen in update_tg_cfs_util(), maybe a more complicated testcase?
>> But since avg.period_contrib of cfs_rq and gcfs_rq are the same this >> should work. >> >>> /* Update parent cfs_rq utilization */ >>> add_positive(&cfs_rq->avg.util_avg, delta); >>> - cfs_rq->avg.util_sum = cfs_rq->avg.util_avg * LOAD_AVG_MAX; >>> + cfs_rq->avg.util_sum = cfs_rq->avg.util_avg * divider; >> >> Looks like that avg.last_update_time of se (group entity), it's gcfs_rq >> and cfs_rq is always the same in update_tg_cfs_[util\|runnable]. >> >> So that means the PELT windows are aligned for cfs_rqs and group se's? > > We want to align util_avg with util_sum and period_contrib otherwise > we might have some unalignment. It's quite similarly to what is done > in attach_entity_load_avg()
I agree.
>> And if we want to enforce this for cfs_rq and task, we have >> sync_entity_load_avg(). > > It's not a matter of syncing the last_update_time
I agree, this is not what you want to achieve here. But syncing 'last_update_time' and 'period_contrib' is what I understand as aligning the decay window (like in attach_entity_load_avg()).
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