linux-kernel - Re: [PATCH 2/4] sched,numa: weigh nearby nodes for task placement on complex NUMA topologies

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Date:	Fri, 9 May 2014 12:03:46 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	riel@...hat.com
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org, mgorman@...e.de,
	chegu_vinod@...com
Subject: Re: [PATCH 2/4] sched,numa: weigh nearby nodes for task placement on
 complex NUMA topologies

On Thu, May 08, 2014 at 01:23:29PM -0400, riel@...hat.com wrote:
>  static inline unsigned long task_weight(struct task_struct *p, int nid)
>  {
> -	unsigned long total_faults;
> +	unsigned long total_faults, score;
>  
>  	if (!p->numa_faults_memory)
>  		return 0;
> @@ -940,15 +997,32 @@ static inline unsigned long task_weight(struct task_struct *p, int nid)
>  	if (!total_faults)
>  		return 0;
>  
> -	return 1000 * task_faults(p, nid) / total_faults;
> +	score = 1000 * task_faults(p, nid);
> +	score += nearby_nodes_score(p, nid, true);
> +
> +	score /= total_faults;
> +
> +	return score;
>  }

So you add an O(nr_nodes) loop to task_weight(), but that in itself is
already called from O(nr_nodes) loops, yielding a total complexity of
O(nr_nodes^2).

This might be fine, but algorithmic complexity should very much be a
part of the changelog I think.

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