linux-kernel - Re: [PATCH v2 4/4] sched/deadline: change cpudl_find() to return bool instead of best

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Date:	Wed, 19 Nov 2014 11:30:08 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"pang.xunlei" <pang.xunlei@...aro.org>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...il.com>
Subject: Re: [PATCH v2 4/4] sched/deadline: change cpudl_find() to return
 bool instead of best_cpu

On Wed, 19 Nov 2014 23:46:22 +0800
"pang.xunlei" <pang.xunlei@...aro.org> wrote:

> cpudl_find() is not a good place to select the best cpu, so leave
> this role to its call site, currently it is find_later_rq() where
> we can do the election of the best cpu according to sd topology.
> 
> Signed-off-by: pang.xunlei <pang.xunlei@...aro.org>
> ---
>  kernel/sched/cpudeadline.c |   15 +++++----------
>  kernel/sched/deadline.c    |   17 ++++++-----------
>  2 files changed, 11 insertions(+), 21 deletions(-)
> 
> diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
> index 3047846..41d3578 100644
> --- a/kernel/sched/cpudeadline.c
> +++ b/kernel/sched/cpudeadline.c
> @@ -100,29 +100,24 @@ static inline int cpudl_maximum(struct cpudl *cp)
>   * @later_mask: a mask to fill in with the selected CPUs (not NULL)
>   * @set_flag: indicate if later_mask should be set
>   *
> - * Returns: int - best CPU (heap maximum if suitable)
> + * Return: (int)bool - CPUs were found
>   */
>  int cpudl_find(struct cpudl *cp, struct task_struct *p,
>  	       struct cpumask *later_mask, int set_flag)
>  {
> -	int best_cpu = -1;
>  	const struct sched_dl_entity *dl_se = &p->dl;
>  
>  	cpumask_and(later_mask, cpu_active_mask, &p->cpus_allowed);
>  	if (cpumask_and(later_mask, later_mask, cp->free_cpus)) {
> -		best_cpu = cpumask_any(later_mask);
> -		goto out;
> +		return 1;
>  	} else if (cpumask_test_cpu(cpudl_maximum(cp), &p->cpus_allowed) &&
>  			dl_time_before(dl_se->deadline, cp->elements[0].dl)) {
> -		best_cpu = cpudl_maximum(cp);
>  		if (set_flag)
> -			cpumask_set_cpu(best_cpu, later_mask);
> +			cpumask_set_cpu(cpudl_maximum(cp), later_mask);
> +		return 1;
>  	}
>  
> -out:
> -	WARN_ON(best_cpu != -1 && !cpu_present(best_cpu));

You lost this warning. It should be moved too.

> -
> -	return best_cpu;
> +	return 0;
>  }
>  
>  /*
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index e8208d0..3e82cf3 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -976,7 +976,7 @@ static void check_preempt_equal_dl(struct rq *rq, struct task_struct *p)
>  	 * let's hope p can move out.
>  	 */
>  	if (rq->curr->nr_cpus_allowed == 1 ||
> -	    cpudl_find(&rq->rd->cpudl, rq->curr, later_mask, 0) == -1)
> +	    !cpudl_find(&rq->rd->cpudl, rq->curr, later_mask, 0))
>  		return;
>  
>  	/*
> @@ -984,7 +984,7 @@ static void check_preempt_equal_dl(struct rq *rq, struct task_struct *p)
>  	 * see if it is pushed or pulled somewhere else.
>  	 */
>  	if (p->nr_cpus_allowed != 1 &&
> -	    cpudl_find(&rq->rd->cpudl, p, later_mask, 0) != -1)
> +	    cpudl_find(&rq->rd->cpudl, p, later_mask, 0))
>  		return;
>  
>  	resched_curr(rq);
> @@ -1189,9 +1189,7 @@ static int find_later_rq(struct task_struct *task)
>  	 * We have to consider system topology and task affinity
>  	 * first, then we can look for a suitable cpu.
>  	 */
> -	best_cpu = cpudl_find(&task_rq(task)->rd->cpudl,
> -			task, later_mask, 1);
> -	if (best_cpu == -1)
> +	if (!cpudl_find(&task_rq(task)->rd->cpudl, task, later_mask, 1))
>  		return -1;
>  
>  	/*
> @@ -1230,12 +1228,9 @@ static int find_later_rq(struct task_struct *task)
>  				return this_cpu;
>  			}
>  
> -			/*
> -			 * Last chance: if best_cpu is valid and is
> -			 * in the mask, that becomes our choice.
> -			 */
> -			if (best_cpu < nr_cpu_ids &&
> -			    cpumask_test_cpu(best_cpu, sched_domain_span(sd))) {
> +			best_cpu = cpumask_first_and(lowest_mask,
> +						sched_domain_span(sd));

Sometimes that 80 character rule isn't the best for readability. But
that is Peter's or Juri's call.

> +			if (best_cpu < nr_cpu_ids) {

The warning should probably go here.

-- Steve

>  				rcu_read_unlock();
>  				return best_cpu;
>  			}

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