linux-kernel - [PATCH V2 1/2] sched/fair: Prevent cpu_busy_time from exceeding actual_cpu

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Date: Mon, 24 Jun 2024 16:20:10 +0800
From: Xuewen Yan <xuewen.yan@...soc.com>
To: <vincent.guittot@...aro.org>, <dietmar.eggemann@....com>,
        <mingo@...hat.com>, <peterz@...radead.org>, <juri.lelli@...hat.com>,
        <qyousef@...alina.io>
CC: <rostedt@...dmis.org>, <bsegall@...gle.com>, <mgorman@...e.de>,
        <bristot@...hat.com>, <vschneid@...hat.com>,
        <christian.loehle@....com>, <vincent.donnefort@....com>,
        <ke.wang@...soc.com>, <di.shen@...soc.com>, <xuewen.yan94@...il.com>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH V2 1/2] sched/fair: Prevent cpu_busy_time from exceeding actual_cpu_capacity

Commit 3e8c6c9aac42 ("sched/fair: Remove task_util from effective utilization in feec()")
changed the PD's util from per-CPU to per-PD capping. But because
the effective_cpu_util() would return a util which maybe bigger
than the actual_cpu_capacity, this could cause the pd_busy_time
calculation errors.
So clamp the cpu_busy_time with the eenv->cpu_cap, which is
the actual_cpu_capacity.

Fixes: 3e8c6c9aac42 ("sched/fair: Remove task_util from effective utilization in feec()")
Signed-off-by: Xuewen Yan <xuewen.yan@...soc.com>
Tested-by: Christian Loehle <christian.loehle@....com>
---
V2:
- change commit message.
- remove the eenv->pd_cap capping in eenv_pd_busy_time(). (Dietmar)
- add Tested-by.
---
 kernel/sched/fair.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8a5b1ae0aa55..5ca6396ef0b7 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7864,16 +7864,17 @@ static inline void eenv_pd_busy_time(struct energy_env *eenv,
 				     struct cpumask *pd_cpus,
 				     struct task_struct *p)
 {
-	unsigned long busy_time = 0;
 	int cpu;
 
+	eenv->pd_busy_time = 0;
+
 	for_each_cpu(cpu, pd_cpus) {
 		unsigned long util = cpu_util(cpu, p, -1, 0);
 
-		busy_time += effective_cpu_util(cpu, util, NULL, NULL);
+		util = effective_cpu_util(cpu, util, NULL, NULL);
+		util = min(eenv->cpu_cap, util);
+		eenv->pd_busy_time += util;
 	}
-
-	eenv->pd_busy_time = min(eenv->pd_cap, busy_time);
 }
 
 /*
-- 
2.25.1