When a task is enqueue the estimated utilization of a CPU is updated
to better support the selection of the required frequency.
However, schedutil is (implicitly) updated by update_load_avg() which
always happens before util_est_{en,de}queue(), thus potentially
introducing a latency between estimated utilization updates and
frequency selections.Let's update util_est at the beginning of enqueue_task_fair(), which will ensure that all schedutil updates will see the most updated estimated utilization value for a CPU. Reported-by: Vincent Guittot <[email protected]> Signed-off-by: Patrick Bellasi <[email protected]> Acked-by: Viresh Kumar <[email protected]> Acked-by: Vincent Guittot <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Vincent Guittot <[email protected]> Cc: [email protected] Cc: [email protected] Fixes: 7f65ea42eb00 ("sched/fair: Add util_est on top of PELT") --- Changes in v3: - add "Acked-by" Vincent tags Changes in v2: - improve comment in enqueue_task_fair() (Peter) - add "Fixes" tag - add "Acked-by" Viresh tag --- kernel/sched/fair.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 748cb054fefd..e497c05aab7f 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5385,6 +5385,14 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) struct cfs_rq *cfs_rq; struct sched_entity *se = &p->se; + /* + * The code below (indirectly) updates schedutil which looks at + * the cfs_rq utilization to select a frequency. + * Let's add the task's estimated utilization to the cfs_rq's + * estimated utilization, before we update schedutil. + */ + util_est_enqueue(&rq->cfs, p); + /* * If in_iowait is set, the code below may not trigger any cpufreq * utilization updates, so do it here explicitly with the IOWAIT flag @@ -5426,7 +5434,6 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) if (!se) add_nr_running(rq, 1); - util_est_enqueue(&rq->cfs, p); hrtick_update(rq); } -- 2.15.1
