Messages in this thread | | | From | Valentin Schneider <> | Subject | Re: [PATCH v2] sched/uclamp: Avoid getting unreasonable ucalmp value when rq is idle | Date | Fri, 02 Jul 2021 13:12:41 +0100 |
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On 02/07/21 12:54, Qais Yousef wrote: > sched/uclamp: Ignore max aggregation if rq is idle > > When a task wakes up on an idle rq, uclamp_rq_util_with() would max > aggregate with rq value. But since there is no task enqueued yet, the > values are stale based on the last task that was running. When the new
Nit: those values are "intentionally stale" for UCLAMP_MAX, per
e496187da710 ("sched/uclamp: Enforce last task's UCLAMP_MAX")
for UCLAMP_MIN we'll set uclamp_none(UCLAMP_MIN) == 0 upon dequeueing the last runnable task, which DTRT.
> task actually wakes up and enqueued, then the rq uclamp values should > reflect that of the newly woken up task effective uclamp values. > > This is a problem particularly for uclamp_max because it default to ^^^^^^^^^^^^ Per the above, it's "only" a problem for UCLAMP_MAX.
> 1024. If a task p with uclamp_max = 512 wakes up, then max aggregation > would ignore the capping that should apply when this task is enqueued, > which is wrong. > > Fix that by ignoring max aggregation if the rq is idle since in that > case the effective uclamp value of the rq will be the ones of the task > that will wake up. >
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