linux-kernel - [PATCH v2 2/2] sched/fair: take into account scheduling domain in select_idle

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Date: Fri, 15 Dec 2023 19:12:56 +0100
From: Keisuke Nishimura <keisuke.nishimura@...ia.fr>
To: Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Abel Wu <wuyun.abel@...edance.com>,
	Josh Don <joshdon@...gle.com>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Valentin Schneider <vschneid@...hat.com>
Cc: Xunlei Pang <xlpang@...ux.alibaba.com>,
	linux-kernel@...r.kernel.org,
	Julia Lawall <julia.lawall@...ia.fr>,
	Keisuke Nishimura <keisuke.nishimura@...ia.fr>
Subject: [PATCH v2 2/2] sched/fair: take into account scheduling domain in select_idle_core()

When picking out a CPU on a task wakeup, select_idle_core() has to take
into account the scheduling domain where the function looks for the CPU.
This is because the "isolcpus" kernel command line option can remove CPUs
from the domain to isolate them from other SMT siblings.

This change replaces the set of CPUs allowed to run the task from
p->cpus_ptr by the intersection of p->cpus_ptr and sched_domain_span(sd)
which is stored in the cpus argument provided by select_idle_cpu.

Fixes: 9fe1f127b913 ("sched/fair: Merge select_idle_core/cpu()")
Signed-off-by: Keisuke Nishimura <keisuke.nishimura@...ia.fr>
Signed-off-by: Julia Lawall <julia.lawall@...ia.fr>
---
V2: - Changed the log message to mention only isolcpus

 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 5e5cef258d3e..7c8883239dfd 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7262,7 +7262,7 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu
 		if (!available_idle_cpu(cpu)) {
 			idle = false;
 			if (*idle_cpu == -1) {
-				if (sched_idle_cpu(cpu) && cpumask_test_cpu(cpu, p->cpus_ptr)) {
+				if (sched_idle_cpu(cpu) && cpumask_test_cpu(cpu, cpus)) {
 					*idle_cpu = cpu;
 					break;
 				}
@@ -7270,7 +7270,7 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu
 			}
 			break;
 		}
-		if (*idle_cpu == -1 && cpumask_test_cpu(cpu, p->cpus_ptr))
+		if (*idle_cpu == -1 && cpumask_test_cpu(cpu, cpus))
 			*idle_cpu = cpu;
 	}
 
-- 
2.34.1