Re: [PATCH 7/9] sched/fair: Do not try to migrate delayed dequeue task

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Nov 28, 2024 at 10:27:48AM +0100, Vincent Guittot wrote:
> Migrating a delayed dequeued task doesn't help in balancing the number
> of runnable tasks in the system.

But it can help balance the weight; furthermore, by moving them to a
lighter queue, they'll get picked sooner and disappear sooner.

Perhaps make it: p->se.sched_delayed && !env->sd->nr_balance_failed ?

> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
>  kernel/sched/fair.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 1b4f1b610543..9d80f3a61082 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9405,11 +9405,15 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
>  
>  	/*
>  	 * We do not migrate tasks that are:
> -	 * 1) throttled_lb_pair, or
> -	 * 2) cannot be migrated to this CPU due to cpus_ptr, or
> -	 * 3) running (obviously), or
> -	 * 4) are cache-hot on their current CPU.
> +	 * 1) delayed dequeued, or
> +	 * 2) throttled_lb_pair, or
> +	 * 3) cannot be migrated to this CPU due to cpus_ptr, or
> +	 * 4) running (obviously), or
> +	 * 5) are cache-hot on their current CPU.
>  	 */
> +	if (p->se.sched_delayed)
> +		return 0;
> +
>  	if (throttled_lb_pair(task_group(p), env->src_cpu, env->dst_cpu))
>  		return 0;
>  
> -- 
> 2.43.0
>