[PATCH 5.7 181/265] sched/cfs: change initial value of runnable_avg

Sasha Levin
2020-06-29T22:06:00Z

From: Vincent Guittot <vincent.guittot@linaro.org>

[ Upstream commit e21cf43406a190adfcc4bfe592768066fb3aaa9b ]

Some performance regression on reaim benchmark have been raised with
commit 070f5e860ee2 ("sched/fair: Take into account runnable_avg to classify group")

The problem comes from the init value of runnable_avg which is initialized
with max value. This can be a problem if the newly forked task is finally
a short task because the group of CPUs is wrongly set to overloaded and
tasks are pulled less agressively.

Set initial value of runnable_avg equals to util_avg to reflect that there
is no waiting time so far.

Fixes: 070f5e860ee2 ("sched/fair: Take into account runnable_avg to classify group")
Reported-by: kernel test robot <rong.a.chen@intel.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200624154422.29166-1-vincent.guittot@linaro.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/sched/fair.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2ae7e30ccb33c..5725199b32dcf 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -807,7 +807,7 @@ void post_init_entity_util_avg(struct task_struct *p)
}
}

- sa->runnable_avg = cpu_scale;
+ sa->runnable_avg = sa->util_avg;

if (p->sched_class != &fair_sched_class) {
/*
--
2.25.1