linux-kernel - Re: [PATCH 1/14] cpumask: simplify sched

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Message-Id: <1257266509.26028.3343.camel@gandalf.stny.rr.com>
Date:	Tue, 03 Nov 2009 11:41:49 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Gregory Haskins <ghaskins@...ell.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH 1/14] cpumask: simplify sched_rt.c

Greg,

I believe this was mostly your code. Can you review this change.

Thanks,

-- Steve


On Tue, 2009-11-03 at 14:53 +1030, Rusty Russell wrote:
> find_lowest_rq() wants to call pick_optimal_cpu() on the intersection
> of sched_domain_span(sd) and lowest_mask.  Rather than doing a cpus_and
> into a temporary, we can open-code it.
> 
> This actually makes the code slightly clearer, IMHO.
> 
> Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
> To: Steven Rostedt <rostedt@...dmis.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> ---
>  kernel/sched_rt.c |   59 +++++++++++++++++++++---------------------------------
>  1 file changed, 23 insertions(+), 36 deletions(-)
> 
> diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
> --- a/kernel/sched_rt.c
> +++ b/kernel/sched_rt.c
> @@ -1115,29 +1115,12 @@ static struct task_struct *pick_next_hig
>  
>  static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask);
>  
> -static inline int pick_optimal_cpu(int this_cpu,
> -				   const struct cpumask *mask)
> -{
> -	int first;
> -
> -	/* "this_cpu" is cheaper to preempt than a remote processor */
> -	if ((this_cpu != -1) && cpumask_test_cpu(this_cpu, mask))
> -		return this_cpu;
> -
> -	first = cpumask_first(mask);
> -	if (first < nr_cpu_ids)
> -		return first;
> -
> -	return -1;
> -}
> -
>  static int find_lowest_rq(struct task_struct *task)
>  {
>  	struct sched_domain *sd;
>  	struct cpumask *lowest_mask = __get_cpu_var(local_cpu_mask);
>  	int this_cpu = smp_processor_id();
>  	int cpu      = task_cpu(task);
> -	cpumask_var_t domain_mask;
>  
>  	if (task->rt.nr_cpus_allowed == 1)
>  		return -1; /* No other targets possible */
> @@ -1167,28 +1150,26 @@ static int find_lowest_rq(struct task_st
>  	 * Otherwise, we consult the sched_domains span maps to figure
>  	 * out which cpu is logically closest to our hot cache data.
>  	 */
> -	if (this_cpu == cpu)
> -		this_cpu = -1; /* Skip this_cpu opt if the same */
> +	if (!cpumask_test_cpu(this_cpu, lowest_mask))
> +		this_cpu = -1; /* Skip this_cpu opt if not among lowest */
>  
> -	if (alloc_cpumask_var(&domain_mask, GFP_ATOMIC)) {
> -		for_each_domain(cpu, sd) {
> -			if (sd->flags & SD_WAKE_AFFINE) {
> -				int best_cpu;
> +	for_each_domain(cpu, sd) {
> +		if (sd->flags & SD_WAKE_AFFINE) {
> +			int best_cpu;
>  
> -				cpumask_and(domain_mask,
> -					    sched_domain_span(sd),
> -					    lowest_mask);
> +			/*
> +			 * "this_cpu" is cheaper to preempt than a
> +			 * remote processor.
> +			 */
> +			if (this_cpu != -1 &&
> +			    cpumask_test_cpu(this_cpu, sched_domain_span(sd)))
> +				return this_cpu;
>  
> -				best_cpu = pick_optimal_cpu(this_cpu,
> -							    domain_mask);
> -
> -				if (best_cpu != -1) {
> -					free_cpumask_var(domain_mask);
> -					return best_cpu;
> -				}
> -			}
> +			best_cpu = cpumask_first_and(lowest_mask,
> +						     sched_domain_span(sd));
> +			if (best_cpu < nr_cpu_ids)
> +				return best_cpu;
>  		}
> -		free_cpumask_var(domain_mask);
>  	}
>  
>  	/*
> @@ -1196,7 +1177,13 @@ static int find_lowest_rq(struct task_st
>  	 * just give the caller *something* to work with from the compatible
>  	 * locations.
>  	 */
> -	return pick_optimal_cpu(this_cpu, lowest_mask);
> +	if (this_cpu != -1)
> +		return this_cpu;
> +
> +	cpu = cpumask_any(lowest_mask);
> +	if (cpu < nr_cpu_ids)
> +		return cpu;
> +	return -1;
>  }
>  
>  /* Will lock the rq it finds */
> 

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