linux-kernel - Re: [PATCH] sched: fix constructing the span cpu mask of sched domain

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Message-ID: <20110506071233.GC23166@elte.hu>
Date:	Fri, 6 May 2011 09:12:33 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Hillf Danton <dhillf@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Mike Galbraith <efault@....de>,
	Yong Zhang <yong.zhang0@...il.com>
Subject: Re: [PATCH] sched: fix constructing the span cpu mask of sched domain


* Hillf Danton <dhillf@...il.com> wrote:

> For a given node, when constructing the cpumask for its sched_domain
> to span, if there is no best node available after searching, further
> efforts could be saved, based on small change in the return value of
> find_next_best_node().
> 
> Signed-off-by: Hillf Danton <dhillf@...il.com>
> ---
> 
> --- a/kernel/sched.c	2011-04-27 11:48:50.000000000 +0800
> +++ b/kernel/sched.c	2011-05-05 20:44:52.000000000 +0800
> @@ -6787,7 +6787,7 @@ init_sched_build_groups(const struct cpu
>   */
>  static int find_next_best_node(int node, nodemask_t *used_nodes)
>  {
> -	int i, n, val, min_val, best_node = 0;
> +	int i, n, val, min_val, best_node = -1;
> 
>  	min_val = INT_MAX;
> 
> @@ -6811,7 +6811,8 @@ static int find_next_best_node(int node,
>  		}
>  	}
> 
> -	node_set(best_node, *used_nodes);
> +	if (best_node != -1)
> +		node_set(best_node, *used_nodes);
>  	return best_node;
>  }
> 
> @@ -6837,7 +6838,8 @@ static void sched_domain_node_span(int n
> 
>  	for (i = 1; i < SD_NODES_PER_DOMAIN; i++) {
>  		int next_node = find_next_best_node(node, &used_nodes);
> -
> +		if (next_node < 0)
> +			break;
>  		cpumask_or(span, span, cpumask_of_node(next_node));
>  	}
>  }

Looks good. I changed the title from:

  sched: fix constructing the span cpu mask of sched domain

to:

  sched: Shorten the constructing of the span cpu mask of sched domain

Because unless i missed some side effect it really does not 'fix' anything, it 
avoids repetitive (and ultimately fruitless) extra work, right?

Thanks,

	Ingo
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