linux-kernel - Re: [PATCH v2 3/4] sched/deadline: add the "set_flag" argument to cpudl

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Date:	Wed, 19 Nov 2014 11:24:51 -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 3/4] sched/deadline: add the "set_flag" argument to
 cpudl_find()

On Wed, 19 Nov 2014 23:46:21 +0800
"pang.xunlei" <pang.xunlei@...aro.org> wrote:

> The call site of cpudl_find() in check_preempt_equal_dl() doesn't
> use later_mask, so add this extra argument to distinquish the case.
> 
> Signed-off-by: pang.xunlei <pang.xunlei@...aro.org>
> ---
>  kernel/sched/cpudeadline.c |    6 ++++--
>  kernel/sched/cpudeadline.h |    2 +-
>  kernel/sched/deadline.c    |    6 +++---
>  3 files changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
> index c01b3aa..3047846 100644
> --- a/kernel/sched/cpudeadline.c
> +++ b/kernel/sched/cpudeadline.c
> @@ -98,11 +98,12 @@ static inline int cpudl_maximum(struct cpudl *cp)
>   * @cp: the cpudl max-heap context
>   * @p: the task
>   * @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)
>   */
>  int cpudl_find(struct cpudl *cp, struct task_struct *p,
> -	       struct cpumask *later_mask)
> +	       struct cpumask *later_mask, int set_flag)

set_flag should be a bool type.

>  {
>  	int best_cpu = -1;
>  	const struct sched_dl_entity *dl_se = &p->dl;
> @@ -114,7 +115,8 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p,
>  	} 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);
> -		cpumask_set_cpu(best_cpu, later_mask);
> +		if (set_flag)
> +			cpumask_set_cpu(best_cpu, later_mask);

I'm not sure this is worth it. cpumask_set_cpu() is rather efficient.

>  	}
>  
>  out:

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