linux-kernel - Re: [PATCH 2/2 RESEND] sched/topology: Optimize topology_span

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Date: Tue, 9 Apr 2024 19:25:06 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Kyle Meyer <kyle.meyer@....com>
Cc: linux-kernel@...r.kernel.org, yury.norov@...il.com,
	linux@...musvillemoes.dk, mingo@...hat.com, peterz@...radead.org,
	juri.lelli@...hat.com, vincent.guittot@...aro.org,
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
	mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
	russ.anderson@....com, dimitri.sivanich@....com, steve.wahl@....com
Subject: Re: [PATCH 2/2 RESEND] sched/topology: Optimize topology_span_sane()

On Tue, Apr 09, 2024 at 10:52:50AM -0500, Kyle Meyer wrote:
> Optimize topology_span_sane() by removing duplicate comparisons.
> 
> The total number of comparisons is reduced from N * (N - 1) to
> N * (N - 1) / 2 (per non-NUMA scheduling domain level).

..

> -	for_each_cpu(i, cpu_map) {
> -		if (i == cpu)
> -			continue;
> +	for_each_cpu_from(i, cpu_map) {

Hmm... I'm not familiar with the for_each_cpu*(), but from the above
it seems only a single comparison? Or i.o.w. can i ever repeat the value?
And what about i < cpu cases?

-- 
With Best Regards,
Andy Shevchenko