Hi Yan,
On 09/12/2020 11:44, Xuewen Yan wrote:
> when a task dequeued, it will update it's util, and cfs_rq_util_change
> would check rq's util, if the cfs_rq->avg.util_est.enqueued is bigger
> than cfs_rq->avg.util_avg, but because the cfs_rq->avg.util_est.enqueued
> didn't be decreased, this would cause bigger cfs_rq_util by mistake,
> as a result, cfs_rq_util_change may change freq unreasonablely.
>
> separate the util_est_dequeue() into util_est_dequeue() and
> util_est_update(), and dequeue the _task_util_est(p) before update util.
The issue is that sugov_update_[shared\|single] -> sugov_get_util() ->
cpu_util_cfs() operates on an old cfs_rq->avg.util_est.enqueued value?
cpu_util_cfs()
if (sched_feat(UTIL_EST))
util = max_t(util, READ_ONCE(rq->cfs.avg.util_est.enqueued))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
dequeue_task_fair() (w/ your patch, moving (1) before (2))
/* (1) update cfs_rq->avg.util_est.enqueued */
util_est_dequeue()
/* (2) potential p->se.avg.util_avg update */
/* 2 for loops */
for_each_sched_entity()
/* this can only lead to a freq change for a root cfs_rq */
(dequeue_entity() ->) update_load_avg() -> cfs_rq_util_change()
-> cpufreq_update_util() ->...-> sugov_update_[shared\|single]
/* (3) potential update p->se.avg.util_est */
util_est_update()
We do need (3) after (2) because of:
util_est_update()
...
ue.enqueued = (task_util(p) | UTIL_AVG_UNCHANGED); task_util
... ^^^^^^^^^^^^^
p->se.avg.util_avg
Did I get this right?
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