Re: [RFC PATCH v7] sched: Fix performance regression introduced by mm_cid

[Aaron Lu <aaron.lu@intel.com>]

On Sun, Apr 16, 2023 at 06:32:17PM -0400, Mathieu Desnoyers wrote:
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 0d18c3969f90..9532cf1a2a44 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2084,8 +2084,10 @@ static inline void dequeue_task(struct rq *rq, struct task_struct *p, int flags)
>  
>  void activate_task(struct rq *rq, struct task_struct *p, int flags)
>  {
> -	if (task_on_rq_migrating(p))
> +	if (task_on_rq_migrating(p)) {
>  		flags |= ENQUEUE_MIGRATED;
> +		sched_mm_cid_migrate_to(rq, p);


I noticed you did this in previous version too but forgot to ask:
is it your intention to only invoke sched_mm_cid_migrate_to() for queued
tasks, i.e. tasks that are being migrated due to load/idle balance etc,
but not those tasks that migrated on wakeup?

I saw you did the corresonding sched_mm_cid_migrate_from() in
set_task_cpu(), which on the other hand includes tasks that migrated due
to wakeup, so it kind of feel weird.

> +	}
>  
>  	enqueue_task(rq, p, flags);
>  
> @@ -3195,6 +3197,7 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
>  			p->sched_class->migrate_task_rq(p, new_cpu);
>  		p->se.nr_migrations++;
>  		rseq_migrate(p);
> +		sched_mm_cid_migrate_from(p);
>  		perf_event_task_migrate(p);
>  	}

Thanks,
Aaron