On Fri, Dec 18, 2020 at 02:12:50PM +0100, Vincent Guittot wrote: > On Fri, 18 Dec 2020 at 10:28, Xuewen Yan <[email protected]> wrote: > > > > From: Xuewen Yan <[email protected]> > > > > CPU (root cfs_rq) estimated utilization (util_est) is currently used in > > dequeue_task_fair() to drive frequency selection before it is updated. > > > > with: > > > > CPU_util : rq->cfs.avg.util_avg > > CPU_util_est : rq->cfs.avg.util_est > > CPU_utilization : max(CPU_util, CPU_util_est) > > task_util : p->se.avg.util_avg > > task_util_est : p->se.avg.util_est > > > > dequeue_task_fair(): > > > > /* (1) CPU_util and task_util update + inform schedutil about > > CPU_utilization changes */ > > for_each_sched_entity() /* 2 loops */ > > (dequeue_entity() ->) update_load_avg() -> cfs_rq_util_change() > > -> cpufreq_update_util() ->...-> sugov_update_[shared\|single] > > -> sugov_get_util() -> cpu_util_cfs() > > > > /* (2) CPU_util_est and task_util_est update */ > > util_est_dequeue() > > > > cpu_util_cfs() uses CPU_utilization which could lead to a false (too > > high) utilization value for schedutil in task ramp-down or ramp-up > > scenarios during task dequeue. > > > > To mitigate the issue split the util_est update (2) into: > > > > (A) CPU_util_est update in util_est_dequeue() > > (B) task_util_est update in util_est_update() > > > > Place (A) before (1) and keep (B) where (2) is. The latter is necessary > > since (B) relies on task_util update in (1). > > > > maybe add a > Fixes: 7f65ea42eb00 ("sched/fair: Add util_est on top of PELT") > > > Signed-off-by: Xuewen Yan <[email protected]> > > Reviewed-by: Dietmar Eggemann <[email protected]> > > Reviewed-by: Vincent Guittot <[email protected]>
Thanks!
