linux-kernel - Re: [PATCH] sched: fix incorrect wait time and wait count statistics

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Date:	Sun, 25 Oct 2015 11:26:10 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Joonwoo Park <joonwoop@...eaurora.org>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH] sched: fix incorrect wait time and wait count statistics

On Sat, Oct 24, 2015 at 10:23:14PM -0700, Joonwoo Park wrote:
> @@ -1069,7 +1069,7 @@ static struct rq *move_queued_task(struct rq *rq, struct task_struct *p, int new
>  {
>  	lockdep_assert_held(&rq->lock);
>  
> -	dequeue_task(rq, p, 0);
> +	dequeue_task(rq, p, DEQUEUE_MIGRATING);
>  	p->on_rq = TASK_ON_RQ_MIGRATING;
>  	set_task_cpu(p, new_cpu);
>  	raw_spin_unlock(&rq->lock);

> @@ -5656,7 +5671,7 @@ static void detach_task(struct task_struct *p, struct lb_env *env)
>  {
>  	lockdep_assert_held(&env->src_rq->lock);
>  
> -	deactivate_task(env->src_rq, p, 0);
> +	deactivate_task(env->src_rq, p, DEQUEUE_MIGRATING);
>  	p->on_rq = TASK_ON_RQ_MIGRATING;
>  	set_task_cpu(p, env->dst_cpu);
>  }

Also note that on both sites we also set TASK_ON_RQ_MIGRATING -- albeit
late. Can't you simply set that earlier (and back to QUEUED later) and
test for task_on_rq_migrating() instead of blowing up the fastpath like
you did?
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