linux-kernel - [PATCH] sched/uclamp: Fix getting unreasonable ucalmp

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Date:   Fri, 18 Jun 2021 15:23:49 +0800
From:   Xuewen Yan <xuewen.yan94@...il.com>
To:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com
Cc:     rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, linux-kernel@...r.kernel.org,
        patrick.bellasi@....com, zhang.lyra@...il.com
Subject: [PATCH] sched/uclamp: Fix getting unreasonable ucalmp_max when rq is idle

From: Xuewen Yan <xuewen.yan@...soc.com>

Now in uclamp_rq_util_with(), when the task != NULL, the uclamp_max as following:
uc_rq_max = rq->uclamp[UCLAMP_MAX].value;
uc_eff_max = uclamp_eff_value(p, UCLAMP_MAX);
uclamp_max = max{uc_rq_max, uc_eff_max};

Consider the following scenario:
(1)the rq is idle, the uc_rq_max is last task's UCLAMP_MAX;
(2)the p's uc_eff_max < uc_rq_max.

The result is the uclamp_max = uc_rq_max instead of uc_eff_max, it is unreasonable.

The scenario often happens in find_energy_efficient_cpu(), when the task has smaller UCLAMP_MAX.

Inserts whether the rq is idle in the uclamp_rq_util_with().

Signed-off-by: Xuewen Yan <xuewen.yan@...soc.com>
---
 kernel/sched/sched.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index a189bec13729..0feef6af89f2 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2550,7 +2550,10 @@ unsigned long uclamp_rq_util_with(struct rq *rq, unsigned long util,
 
 	if (p) {
 		min_util = max(min_util, uclamp_eff_value(p, UCLAMP_MIN));
-		max_util = max(max_util, uclamp_eff_value(p, UCLAMP_MAX));
+		if (rq->uclamp_flags & UCLAMP_FLAG_IDLE)
+			max_util = uclamp_eff_value(p, UCLAMP_MAX);
+		else
+			max_util = max(max_util, uclamp_eff_value(p, UCLAMP_MAX));
 	}
 
 	/*
-- 
2.25.1