Re: [PATCH v3 1/2] sched/rt: Check to push the task when changing its affinity

[Steven Rostedt <rostedt@goodmis.org>]

On Sun,  8 Feb 2015 23:51:25 +0800
Xunlei Pang <pang.xunlei@linaro.org> wrote:


> +	if (new_weight > 1 &&
> +	    rt_task(rq->curr) &&
> +	    !test_tsk_need_resched(rq->curr)) {
> +		/*
> +		 * We own p->pi_lock and rq->lock. rq->lock might
> +		 * get released when doing direct pushing, however
> +		 * p->pi_lock is always held, so it's safe to assign
> +		 * the new_mask and new_weight to p below.
> +		 */
> +		if (!task_running(rq, p)) {
> +			cpumask_copy(&p->cpus_allowed, new_mask);
> +			p->nr_cpus_allowed = new_weight;
> +			direct_push = 1;
> +		} else if (cpumask_test_cpu(task_cpu(p), new_mask)) {
> +			cpumask_copy(&p->cpus_allowed, new_mask);
> +			p->nr_cpus_allowed = new_weight;
> +			if (!cpupri_find(&rq->rd->cpupri, p, NULL))
> +				goto update;
> +
> +			/*
> +			 * At this point, current task gets migratable most
> +			 * likely due to the change of its affinity, let's
> +			 * figure out if we can migrate it.
> +			 *
> +			 * Is there any task with the same priority as that
> +			 * of current task? If found one, we should resched.
> +			 * NOTE: The target may be unpushable.
> +			 */
> +			if (p->prio == rq->rt.highest_prio.next) {
> +				/* One target just in pushable_tasks list. */
> +				requeue_task_rt(rq, p, 0);

What's the purpose of the requeue_task_rt() here?

> +				preempt_push = 1;
> +			} else if (rq->rt.rt_nr_total > 1) {
> +				struct task_struct *next;
> +
> +				requeue_task_rt(rq, p, 0);

And here? It may just be late and I'm tired, but it's not obvious to me.

Thanks,

-- Steve

> +				next = peek_next_task_rt(rq);
> +				if (next != p && next->prio == p->prio)
> +					preempt_push = 1;
> +			}
> +		}
> +	}
>