linux-kernel - Re: [PATCH RFC 5/5] sched,numa: find the preferred nid with complex NUMA topology

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Message-ID: <20141012145623.GI3015@worktop>
Date:	Sun, 12 Oct 2014 16:56:23 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	riel@...hat.com
Cc:	linux-kernel@...r.kernel.org, mgorman@...e.de, chegu_vinod@...com,
	mingo@...nel.org, efault@....de, vincent.guittot@...aro.org
Subject: Re: [PATCH RFC 5/5] sched,numa: find the preferred nid with complex
 NUMA topology

On Wed, Oct 08, 2014 at 03:37:30PM -0400, riel@...hat.com wrote:
> +static int preferred_group_nid(struct task_struct *p, int nid)
> +{
> +	nodemask_t nodes;
> +	int hops;
> +
> +	/* Direct connections between all NUMA nodes. */
> +	if (sched_numa_topology_type == NUMA_DIRECT)
> +		return nid;
> +
> +	/*
> +	 * On a system with glueless mesh NUMA topology, group_weight
> +	 * scores nodes according to the number of NUMA hinting faults on
> +	 * both the node itself, and on nearby nodes.
> +	 */
> +	if (sched_numa_topology_type == NUMA_GLUELESS_MESH) {
> +		unsigned long score, max_score = 0;
> +		int node, max_node = nid;
> +
> +		hops = sched_domains_numa_levels;
> +
> +		for_each_online_node(node) {
> +			score = group_weight(p, node, hops);
> +			if (score > max_score) {
> +				max_score = score;
> +				max_node = node;
> +			}
> +		}
> +		return max_node;
> +	}

This too is O(nr_nodes^2), right?
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