Re: [RFCv5 PATCH 34/46] sched: Enable idle balance to pull single task towards cpu with higher capacity

[Peter Zijlstra]

On Tue, Jul 07, 2015 at 07:24:17PM +0100, Morten Rasmussen wrote:
> +++ b/kernel/sched/fair.c
> @@ -7569,6 +7569,13 @@ static int need_active_balance(struct lb_env *env)
>  			return 1;
>  	}
>  
> +	if ((capacity_of(env->src_cpu) < capacity_of(env->dst_cpu)) &&
> +				env->src_rq->cfs.h_nr_running == 1 &&
> +				cpu_overutilized(env->src_cpu) &&
> +				!cpu_overutilized(env->dst_cpu)) {
> +			return 1;
> +	}
> +
>  	return unlikely(sd->nr_balance_failed > sd->cache_nice_tries+2);
>  }

Doesn't this allow for a nice game of ping-pong? Where if a task runs on
CPU X and generates interrupts there, its capacity will lower and we'll
migrate it over to CPU Y because that isn't receiving interrupts.

Now the task is running on Y, will generate interrupts there, and sees X
as a more attractive destination.

goto 1
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