linux-kernel - [PATCH V2 2/2] sched/fair: Use actual_cpu_capacity everywhere in util_fits

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Date: Mon, 24 Jun 2024 16:20:11 +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 2/2] sched/fair: Use actual_cpu_capacity everywhere in util_fits_cpu()

Commit f1f8d0a22422 ("sched/cpufreq: Take cpufreq feedback into account")
introduced get_actual_cpu_capacity(), and it had aggregated the
different pressures applied on the capacity of CPUs.
And in util_fits_cpu(), it would return true when uclamp_max
is smaller than SCHED_CAPACITY_SCALE, althought the uclamp_max
is bigger than actual_cpu_capacity.

So use actual_cpu_capacity everywhere in util_fits_cpu() to
cover all cases.

Signed-off-by: Xuewen Yan <xuewen.yan@...soc.com>
---
 kernel/sched/fair.c | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5ca6396ef0b7..9c16ae192217 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4980,7 +4980,7 @@ static inline int util_fits_cpu(unsigned long util,
 				int cpu)
 {
 	unsigned long capacity = capacity_of(cpu);
-	unsigned long capacity_orig;
+	unsigned long capacity_actual;
 	bool fits, uclamp_max_fits;
 
 	/*
@@ -4992,15 +4992,15 @@ static inline int util_fits_cpu(unsigned long util,
 		return fits;
 
 	/*
-	 * We must use arch_scale_cpu_capacity() for comparing against uclamp_min and
+	 * We must use actual_cpu_capacity() for comparing against uclamp_min and
 	 * uclamp_max. We only care about capacity pressure (by using
 	 * capacity_of()) for comparing against the real util.
 	 *
 	 * If a task is boosted to 1024 for example, we don't want a tiny
 	 * pressure to skew the check whether it fits a CPU or not.
 	 *
-	 * Similarly if a task is capped to arch_scale_cpu_capacity(little_cpu), it
-	 * should fit a little cpu even if there's some pressure.
+	 * Similarly if a task is capped to actual_cpu_capacity, it should fit
+	 * the cpu even if there's some pressure.
 	 *
 	 * Only exception is for HW or cpufreq pressure since it has a direct impact
 	 * on available OPP of the system.
@@ -5011,7 +5011,7 @@ static inline int util_fits_cpu(unsigned long util,
 	 * For uclamp_max, we can tolerate a drop in performance level as the
 	 * goal is to cap the task. So it's okay if it's getting less.
 	 */
-	capacity_orig = arch_scale_cpu_capacity(cpu);
+	capacity_actual = get_actual_cpu_capacity(cpu);
 
 	/*
 	 * We want to force a task to fit a cpu as implied by uclamp_max.
@@ -5039,7 +5039,7 @@ static inline int util_fits_cpu(unsigned long util,
 	 *     uclamp_max request.
 	 *
 	 *   which is what we're enforcing here. A task always fits if
-	 *   uclamp_max <= capacity_orig. But when uclamp_max > capacity_orig,
+	 *   uclamp_max <= capacity_actual. But when uclamp_max > capacity_actual,
 	 *   the normal upmigration rules should withhold still.
 	 *
 	 *   Only exception is when we are on max capacity, then we need to be
@@ -5050,8 +5050,8 @@ static inline int util_fits_cpu(unsigned long util,
 	 *     2. The system is being saturated when we're operating near
 	 *        max capacity, it doesn't make sense to block overutilized.
 	 */
-	uclamp_max_fits = (capacity_orig == SCHED_CAPACITY_SCALE) && (uclamp_max == SCHED_CAPACITY_SCALE);
-	uclamp_max_fits = !uclamp_max_fits && (uclamp_max <= capacity_orig);
+	uclamp_max_fits = (capacity_actual == SCHED_CAPACITY_SCALE) && (uclamp_max == SCHED_CAPACITY_SCALE);
+	uclamp_max_fits = !uclamp_max_fits && (uclamp_max <= capacity_actual);
 	fits = fits || uclamp_max_fits;
 
 	/*
@@ -5086,8 +5086,7 @@ static inline int util_fits_cpu(unsigned long util,
 	 * handle the case uclamp_min > uclamp_max.
 	 */
 	uclamp_min = min(uclamp_min, uclamp_max);
-	if (fits && (util < uclamp_min) &&
-	    (uclamp_min > get_actual_cpu_capacity(cpu)))
+	if (fits && (util < uclamp_min) && (uclamp_min > capacity_actual))
 		return -1;
 
 	return fits;
-- 
2.25.1