linux-kernel - [PATCH 1/7 v3] sched/fair: Filter false overloaded

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Message-ID: <20250228134000.1226665-2-vincent.guittot@linaro.org>
Date: Fri, 28 Feb 2025 14:39:54 +0100
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,
	vschneid@...hat.com,
	lukasz.luba@....com,
	rafael.j.wysocki@...el.com,
	pierre.gondois@....com,
	linux-kernel@...r.kernel.org
Cc: qyousef@...alina.io,
	hongyan.xia2@....com,
	christian.loehle@....com,
	luis.machado@....com,
	qperret@...gle.com,
	Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH 1/7 v3] sched/fair: Filter false overloaded_group case for EAS

With EAS, a group should be set overloaded if at least 1 CPU in the group
is overutilized but it can happen that a CPU is fully utilized by tasks
because of clamping the compute capacity of the CPU. In such case, the CPU
is not overutilized and as a result should not be set overloaded as well.

group_overloaded being a higher priority than group_misfit, such group can
be selected as the busiest group instead of a group with a mistfit task
and prevents load_balance to select the CPU with the misfit task to pull
the latter on a fitting CPU.

Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
Tested-by: Pierre Gondois <pierre.gondois@....com>
---
 kernel/sched/fair.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 857808da23d8..d3d1a2ba6b1a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9931,6 +9931,7 @@ struct sg_lb_stats {
 	unsigned int group_asym_packing;	/* Tasks should be moved to preferred CPU */
 	unsigned int group_smt_balance;		/* Task on busy SMT be moved */
 	unsigned long group_misfit_task_load;	/* A CPU has a task too big for its capacity */
+	unsigned int group_overutilized;	/* At least one CPU is overutilized in the group */
 #ifdef CONFIG_NUMA_BALANCING
 	unsigned int nr_numa_running;
 	unsigned int nr_preferred_running;
@@ -10163,6 +10164,13 @@ group_has_capacity(unsigned int imbalance_pct, struct sg_lb_stats *sgs)
 static inline bool
 group_is_overloaded(unsigned int imbalance_pct, struct sg_lb_stats *sgs)
 {
+	/*
+	 * With EAS and uclamp, 1 CPU in the group must be overutilized to
+	 * consider the group overloaded.
+	 */
+	if (sched_energy_enabled() && !sgs->group_overutilized)
+		return false;
+
 	if (sgs->sum_nr_running <= sgs->group_weight)
 		return false;
 
@@ -10374,8 +10382,10 @@ static inline void update_sg_lb_stats(struct lb_env *env,
 		nr_running = rq->nr_running;
 		sgs->sum_nr_running += nr_running;
 
-		if (cpu_overutilized(i))
+		if (cpu_overutilized(i)) {
 			*sg_overutilized = 1;
+			sgs->group_overutilized = 1;
+		}
 
 		/*
 		 * No need to call idle_cpu() if nr_running is not 0
-- 
2.43.0