Messages in this thread | | | Subject | Re: [PATCH v2] sched/pelt: sync util/runnable_sum with PELT window when propagating | From | Dietmar Eggemann <> | Date | Wed, 20 May 2020 12:29:57 +0200 |
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On 19/05/2020 17:41, Vincent Guittot wrote: > On Tue, 19 May 2020 at 12:28, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote: >> >> On 06/05/2020 17:53, Vincent Guittot wrote:
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>>> diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c >>> index b647d04d9c8b..1feff80e7e45 100644 >>> --- a/kernel/sched/pelt.c >>> +++ b/kernel/sched/pelt.c >>> @@ -237,6 +237,30 @@ ___update_load_sum(u64 now, struct sched_avg *sa, >>> return 1; >>> } >>> >>> +/* >>> + * When syncing *_avg with *_sum, we must take into account the current >>> + * position in the PELT segment otherwise the remaining part of the segment >>> + * will be considered as idle time whereas it's not yet elapsed and this will >>> + * generate unwanted oscillation in the range [1002..1024[. >>> + * >>> + * The max value of *_sum varies with the position in the time segment and is >>> + * equals to : >>> + * >>> + * LOAD_AVG_MAX*y + sa->period_contrib >>> + * >>> + * which can be simplified into: >>> + * >>> + * LOAD_AVG_MAX - 1024 + sa->period_contrib >>> + * >>> + * because LOAD_AVG_MAX*y == LOAD_AVG_MAX-1024 >> >> Isn't this rather '~' instead of '==', even for y^32 = 0.5 ? >> >> 47742 * 0.5^(1/32) ~ 47742 - 1024 > > With integer precision and the runnable_avg_yN_inv array, you've got > exactly 1024
Ah, OK, I forgot about this and that this is related to commit 625ed2bf049d ("sched/cfs: Make util/load_avg more stable").
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