linux-kernel - Re: [PATCH 1/6] sched/topology: introduce for_each_numa_hop_node() / sched_numa_hop

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Message-ID: <Z2Hz2NW-J06BuuHj@slm.duckdns.org>
Date: Tue, 17 Dec 2024 11:57:44 -1000
From: Tejun Heo <tj@...nel.org>
To: Andrea Righi <arighi@...dia.com>
Cc: David Vernet <void@...ifault.com>, Changwoo Min <changwoo@...lia.com>,
	Yury Norov <yury.norov@...il.com>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] sched/topology: introduce for_each_numa_hop_node() /
 sched_numa_hop_node()

Hello,

On Tue, Dec 17, 2024 at 10:32:26AM +0100, Andrea Righi wrote:
...
> +int sched_numa_hop_node(nodemask_t *hop_nodes, int start, unsigned int state)
> +{
> +	int dist, n, min_node, min_dist;
> +
> +	if (state >= NR_NODE_STATES)
> +		return NUMA_NO_NODE;
> +
> +	min_node = NUMA_NO_NODE;
> +	min_dist = INT_MAX;
> +
> +	for_each_node_state(n, state) {
> +		if (n == start || node_isset(n, *hop_nodes))
> +			continue;
> +		dist = node_distance(start, n);
> +		if (dist < min_dist) {
> +			min_dist = dist;
> +			min_node = n;
> +		}
> +	}
> +	if (min_node != NUMA_NO_NODE)
> +		node_set(min_node, *hop_nodes);
> +
> +	return min_node;
> +}

So, this would work but given that there is nothing dynamic about this
ordering, would it make more sense to build the ordering and store it
per-node? Then, the iteration just becomes walking that array.

Thanks.

-- 
tejun