linux-kernel - [PATCH] sched/fair: Check idle_cpu in select_idle

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Date:   Sun, 10 Oct 2021 02:09:41 +0800
From:   Tao Zhou <tao.zhou@...ux.dev>
To:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Cc:     Tao Zhou <tao.zhou@...ux.dev>
Subject: [PATCH] sched/fair: Check idle_cpu in select_idle_core/cpu()

In select_idle_core(), the idle core returned may have no cpu
allowed. I think the idle core returned for the task is the one
that can be allowed to run. I insist on this semantics.

In select_idle_cpu(), if select_idle_core() can not find the
idle core, one reason is that the core is not allowed for the
task, but the core itself is idle from the point of
sds->has_idle_cores. I insist on this semantics.

No others, just two additional check.
---
 kernel/sched/fair.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f6a05d9b5443..a44aca5095d3 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6213,7 +6213,7 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu
 			*idle_cpu = cpu;
 	}
 
-	if (idle)
+	if (idle && *idle_cpu != -1)
 		return core;
 
 	cpumask_andnot(cpus, cpus, cpu_smt_mask(core));
@@ -6324,7 +6324,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
 		}
 	}
 
-	if (has_idle_core)
+	if (has_idle_core && *idle_cpu != -1)
 		set_idle_cores(target, false);
 
 	if (sched_feat(SIS_PROP) && !has_idle_core) {
-- 
2.32.0