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From:   Qais Yousef <qyousef@layalina.io>
To:     Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc:     linux-kernel@vger.kernel.org, Lukasz Luba <lukasz.luba@arm.com>,
        Wei Wang <wvw@google.com>, Xuewen Yan <xuewen.yan94@gmail.com>,
        Hank <han.lin@mediatek.com>,
        Jonathan JMChen <Jonathan.JMChen@mediatek.com>,
        Hongyan Xia <hongyan.xia2@arm.com>,
        Qais Yousef <qyousef@layalina.io>
Subject: [PATCH v5 2/3] sched/uclamp: Ignore (util == 0) optimization in feec() when p_util_max = 0
Date:   Sun, 17 Sep 2023 00:29:54 +0100
Message-Id: <20230916232955.2099394-3-qyousef@layalina.io>
In-Reply-To: <20230916232955.2099394-1-qyousef@layalina.io>
References: <20230916232955.2099394-1-qyousef@layalina.io>
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find_energy_efficient_cpu() bails out early if effective util of the
task is 0 as the delta at this point will be zero and there's nothing
for EAS to do. When uclamp is being used, this could lead to wrong
decisions when uclamp_max is set to 0. In this case the task is capped
to performance point 0, but it is actually running and consuming energy
and we can benefit from EAS energy calculations.

Rework the condition so that it bails out when both util and uclamp_min
are 0.

We can do that without needing to use uclamp_task_util(); remove it.

Fixes: d81304bc6193 ("sched/uclamp: Cater for uclamp in find_energy_efficient_cpu()'s early exit condition")
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Qais Yousef (Google) <qyousef@layalina.io>
---
 kernel/sched/fair.c | 18 +-----------------
 1 file changed, 1 insertion(+), 17 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 3a0a28a0b9c7..0d0582e02409 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4560,22 +4560,6 @@ static inline unsigned long task_util_est(struct task_struct *p)
 	return max(task_util(p), _task_util_est(p));
 }
 
-#ifdef CONFIG_UCLAMP_TASK
-static inline unsigned long uclamp_task_util(struct task_struct *p,
-					     unsigned long uclamp_min,
-					     unsigned long uclamp_max)
-{
-	return clamp(task_util_est(p), uclamp_min, uclamp_max);
-}
-#else
-static inline unsigned long uclamp_task_util(struct task_struct *p,
-					     unsigned long uclamp_min,
-					     unsigned long uclamp_max)
-{
-	return task_util_est(p);
-}
-#endif
-
 static inline void util_est_enqueue(struct cfs_rq *cfs_rq,
 				    struct task_struct *p)
 {
@@ -7687,7 +7671,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
 	target = prev_cpu;
 
 	sync_entity_load_avg(&p->se);
-	if (!uclamp_task_util(p, p_util_min, p_util_max))
+	if (!task_util_est(p) && p_util_min == 0)
 		goto unlock;
 
 	eenv_task_busy_time(&eenv, p, prev_cpu);
-- 
2.34.1