linux-kernel - [PATCH] sched/fair: remove util

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Date:   Thu,  6 Jul 2023 15:51:44 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org
Cc:     qyousef@...alina.io, Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH] sched/fair: remove util_est boosting

There is no need to use runnable_avg when estimating util_est and that
even generates wrong behavior because one includes blocked tasks whereas
the other one doesn't. This can lead to accounting twice the waking task p,
once with the blocked runnable_avg and another one when adding its
util_est.

cpu's runnable_avg is already used when computing util_avg which is then
compared with util_est.

In some situation, feec will not select prev_cpu but another one on the
same performance domain because of higher max_util

Fixes: 7d0583cf9ec7 ("sched/fair, cpufreq: Introduce 'runnable boosting'")
Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 kernel/sched/fair.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a80a73909dc2..77c9f5816c31 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7289,9 +7289,6 @@ cpu_util(int cpu, struct task_struct *p, int dst_cpu, int boost)
 
 		util_est = READ_ONCE(cfs_rq->avg.util_est.enqueued);
 
-		if (boost)
-			util_est = max(util_est, runnable);
-
 		/*
 		 * During wake-up @p isn't enqueued yet and doesn't contribute
 		 * to any cpu_rq(cpu)->cfs.avg.util_est.enqueued.
-- 
2.34.1