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

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Date: Wed, 10 Jan 2024 18:16:30 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Keisuke Nishimura <keisuke.nishimura@...ia.fr>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org, 
	Dietmar Eggemann <dietmar.eggemann@....com>, Mel Gorman <mgorman@...e.de>, 
	Valentin Schneider <vschneid@...hat.com>, Julia Lawall <julia.lawall@...ia.fr>, 
	Xunlei Pang <xlpang@...ux.alibaba.com>, Abel Wu <wuyun.abel@...edance.com>
Subject: Re: [PATCH v2 2/2 RESEND] sched/fair: take into account scheduling
 domain in select_idle_core()

On Wed, 10 Jan 2024 at 14:19, Keisuke Nishimura
<keisuke.nishimura@...ia.fr> wrote:
>
> 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>

Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>

> ---
> 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 66457d4b8965..e2b4e0396af8 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7289,7 +7289,7 @@ 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;
>                                 }
> @@ -7297,7 +7297,7 @@ 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
>