Re: [PATCH 04/10] sched/fair: Dynamically update cfs_overload_cpus

[Peter Zijlstra <peterz@infradead.org>]

On Mon, Oct 22, 2018 at 07:59:35AM -0700, Steve Sistare wrote:
> An overloaded CPU has more than 1 runnable task.  When a CFS task wakes
> on a CPU, if h_nr_running transitions from 1 to more, then set the CPU in
> the cfs_overload_cpus bitmap.  When a CFS task sleeps, if h_nr_running
> transitions from 2 to less, then clear the CPU in cfs_overload_cpus.

> @@ -5111,8 +5147,12 @@ static inline void hrtick_update(struct rq *rq)
>  		update_cfs_group(se);
>  	}
>  
> -	if (!se)
> +	if (!se) {
>  		add_nr_running(rq, 1);
> +		if (prev_nr == 1)
> +			overload_set(rq);
> +
> +	}

This is very similar to what RT already has, except they also track if
the tasks in question is in fact migratable (p->nr_cpus_allowed > 1).

And similarly, it might make sense to use the sparse mask thing over
there.