On 15/12/2020 13:56, Xuewen Yan wrote: > On Tue, Dec 15, 2020 at 5:39 PM Vincent Guittot > <vincent.guit...@linaro.org> wrote: >> >> On Mon, 14 Dec 2020 at 19:46, Dietmar Eggemann <dietmar.eggem...@arm.com> >> wrote: >>> >>> On 11/12/2020 13:03, Ryan Y wrote:
[...] >>> It's true that 'sugov_get_util() -> cpu_util_cfs()' can use >>> rq->cfs.avg.util_est.enqueued before _task_util_est(p) is subtracted >>> from it. >>> >>> But isn't rq->cfs.avg.util_est.enqueued (in this case 601) always close >>> to rq->cfs.avg.util_avg (597) since the task was just running? >>> The cfs_rq utilization contains a blocked (sleeping) task. >> >> There will be a difference if the task alternates long and short runs >> in which case util_avg is lower than util_est. But even in this case, >> the freq will be update at next enqueue/dequeue/tick. >> The only real case could be when cpu goes idle in shallow state (WFI) >> which is impacted by the freq/voltage. But even in this case, the >> situation should not be long >> >> That being said, I agree that the value used by schedutil is not >> correct at dequeue Ok, makes sense. > Hi Dietmar, > > as Vincent said, like the following scenario: > running sleep > running sleep > |---------------------------------------| > |--------| > > ^^ > at the ^^ time, the util_avg is lower than util_est. > we hope that the CPU frequency would be reduced as soon as possible after > the task is dequeued. But the issue affects the sensitivity of cpu > frequency reduce. > worse, since the time, if there is no task enqueue or other scenarios where > the > load is updated, the cpu may always maintain a high frequency. > > if keep the util_est_dequeue as it is, are there other concerns, > or this patch would affect other places of system? I see. So essentially this could have an effect in task ramp-down and ramp-up scenarios. periodic ramp-down task [8/16 -> 4/16 -> 1/16ms], 3 consecutive dequeue_task_fair(): task0-0-1690 [000] 43.677788: sched_pelt_se: cpu=0 path=(null) comm=task0-0 pid=1690 load=283 runnable=283 util=283 update_time=43333963776 task0-0-1690 [000] 43.677792: sched_pelt_cfs: cpu=0 path=/ load=283 runnable=283 util=283 update_time=43333963776 task0-0-1690 [000] 43.677798: bprint: sugov_get_util: CPU0 rq->cfs.avg.util_avg=283 rq->cfs.avg.util_est.enqueued=249 task0-0-1690 [000] 43.677803: sched_util_est_cfs: cpu=0 path=/ enqueued=0 ewma=0 util=283 task0-0-1690 [000] 43.677805: sched_util_est_se: cpu=0 path=(null) comm=task0-0 pid=1690 enqueued=283 ewma=283 util=283 task0-0-1690 [000] 43.677810: bprint: dequeue_task_fair: CPU0 [task0-0 1690] rq->cfs.avg.util_avg=[270->283] rq->cfs.avg.util_est.enqueued=[249->0] task0-0-1690 [000] 43.698764: sched_pelt_se: cpu=0 path=(null) comm=task0-0 pid=1690 load=247 runnable=248 util=248 update_time=43363011584 task0-0-1690 [000] 43.698768: sched_pelt_cfs: cpu=0 path=/ load=248 runnable=248 util=248 update_time=43363011584 --> task0-0-1690 [000] 43.698774: bprint: sugov_get_util: CPU0 rq->cfs.avg.util_avg=248 rq->cfs.avg.util_est.enqueued=283 <-- !!! task0-0-1690 [000] 43.698778: sched_util_est_cfs: cpu=0 path=/ enqueued=0 ewma=0 util=248 task0-0-1690 [000] 43.698780: sched_util_est_se: cpu=0 path=(null) comm=task0-0 pid=1690 enqueued=249 ewma=274 util=248 task0-0-1690 [000] 43.698785: bprint: dequeue_task_fair: CPU0 [task0-0 1690] rq->cfs.avg.util_avg=[228->248] rq->cfs.avg.util_est.enqueued=[283->0] task0-0-1690 [000] 43.714120: sched_pelt_se: cpu=0 path=(null) comm=task0-0 pid=1690 load=183 runnable=183 util=183 update_time=43384443904 task0-0-1690 [000] 43.714125: sched_pelt_cfs: cpu=0 path=/ load=183 runnable=183 util=183 update_time=43384443904 --> task0-0-1690 [000] 43.714131: bprint: sugov_get_util: CPU0 rq->cfs.avg.util_avg=183 rq->cfs.avg.util_est.enqueued=275 <-- !!! task0-0-1690 [000] 43.714135: sched_util_est_cfs: cpu=0 path=/ enqueued=0 ewma=0 util=183 task0-0-1690 [000] 43.714138: sched_util_est_se: cpu=0 path=(null) comm=task0-0 pid=1690 enqueued=183 ewma=251 util=183 task0-0-1690 [000] 43.714142: bprint: dequeue_task_fair: CPU0 [task0-0 1690] rq->cfs.avg.util_avg=[163->183] rq->cfs.avg.util_est.enqueued=[275->0]
