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Subject[tip: sched/core] sched/fair: Return early from update_tg_cfs_load() if delta == 0
The following commit has been merged into the sched/core branch of tip:

Commit-ID: 83c5e9d573e1f0757f324d01adb6ee77b49c3f0e
Gitweb: https://git.kernel.org/tip/83c5e9d573e1f0757f324d01adb6ee77b49c3f0e
Author: Dietmar Eggemann <dietmar.eggemann@arm.com>
AuthorDate: Tue, 01 Jun 2021 10:36:16 +02:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 17 Jun 2021 14:11:42 +02:00

sched/fair: Return early from update_tg_cfs_load() if delta == 0

In case the _avg delta is 0 there is no need to update se's _avg
(level n) nor cfs_rq's _avg (level n-1). These values stay the same.

Since cfs_rq's _avg isn't changed, i.e. no load is propagated down,
cfs_rq's _sum should stay the same as well.

So bail out after se's _sum has been updated.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20210601083616.804229-1-dietmar.eggemann@arm.com
---
kernel/sched/fair.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 198514d..06c8ba7 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3502,9 +3502,12 @@ update_tg_cfs_load(struct cfs_rq *cfs_rq, struct sched_entity *se, struct cfs_rq
load_sum = (s64)se_weight(se) * runnable_sum;
load_avg = div_s64(load_sum, divider);

+ se->avg.load_sum = runnable_sum;
+
delta = load_avg - se->avg.load_avg;
+ if (!delta)
+ return;

- se->avg.load_sum = runnable_sum;
se->avg.load_avg = load_avg;

add_positive(&cfs_rq->avg.load_avg, delta);
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