linux-kernel - [tip: sched/core] sched/fair: Return early from update_tg_cfs

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Date:   Fri, 18 Jun 2021 08:46:07 -0000
From:   "tip-bot2 for Dietmar Eggemann" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
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@....com>
AuthorDate:    Tue, 01 Jun 2021 10:36:16 +02:00
Committer:     Peter Zijlstra <peterz@...radead.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@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.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);