[PATCH v6 9/9] sched/fair: don't init util/runnable_avg for !fair task

From: Chengming Zhou
Date: Thu Aug 18 2022 - 08:49:17 EST


post_init_entity_util_avg() init task util_avg according to the cpu util_avg
at the time of fork, which will decay when switched_to_fair() some time later,
we'd better to not set them at all in the case of !fair task.

Suggested-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
---
kernel/sched/fair.c | 28 ++++++++++++++--------------
1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 93d7c7b110dd..621bd19e10ae 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -833,20 +833,6 @@ void post_init_entity_util_avg(struct task_struct *p)
long cpu_scale = arch_scale_cpu_capacity(cpu_of(rq_of(cfs_rq)));
long cap = (long)(cpu_scale - cfs_rq->avg.util_avg) / 2;

- if (cap > 0) {
- if (cfs_rq->avg.util_avg != 0) {
- sa->util_avg = cfs_rq->avg.util_avg * se->load.weight;
- sa->util_avg /= (cfs_rq->avg.load_avg + 1);
-
- if (sa->util_avg > cap)
- sa->util_avg = cap;
- } else {
- sa->util_avg = cap;
- }
- }
-
- sa->runnable_avg = sa->util_avg;
-
if (p->sched_class != &fair_sched_class) {
/*
* For !fair tasks do:
@@ -861,6 +847,20 @@ void post_init_entity_util_avg(struct task_struct *p)
se->avg.last_update_time = cfs_rq_clock_pelt(cfs_rq);
return;
}
+
+ if (cap > 0) {
+ if (cfs_rq->avg.util_avg != 0) {
+ sa->util_avg = cfs_rq->avg.util_avg * se->load.weight;
+ sa->util_avg /= (cfs_rq->avg.load_avg + 1);
+
+ if (sa->util_avg > cap)
+ sa->util_avg = cap;
+ } else {
+ sa->util_avg = cap;
+ }
+ }
+
+ sa->runnable_avg = sa->util_avg;
}

#else /* !CONFIG_SMP */
--
2.37.2