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

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Date: Wed, 20 Mar 2024 11:32:05 -0700
From: Yury Norov <yury.norov@...il.com>
To: Kyle Meyer <kyle.meyer@....com>
Cc: andriy.shevchenko@...ux.intel.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,
	linux-kernel@...r.kernel.org, russ.anderson@....com,
	dimitri.sivanich@....com, steve.wahl@....com
Subject: Re: [PATCH 2/2] sched/topology: Optimize topology_span_sane()

On Tue, Mar 19, 2024 at 01:51:48PM -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).
> 
> Signed-off-by: Kyle Meyer <kyle.meyer@....com>

Reviewed-by: Yury Norov <yury.norov@...il.com>

> ---
>  kernel/sched/topology.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index 99ea5986038c..b6bcafc09969 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -2347,7 +2347,7 @@ static struct sched_domain *build_sched_domain(struct sched_domain_topology_leve
>  static bool topology_span_sane(struct sched_domain_topology_level *tl,
>  			      const struct cpumask *cpu_map, int cpu)
>  {
> -	int i;
> +	int i = cpu + 1;
>  
>  	/* NUMA levels are allowed to overlap */
>  	if (tl->flags & SDTL_OVERLAP)
> @@ -2359,9 +2359,7 @@ static bool topology_span_sane(struct sched_domain_topology_level *tl,
>  	 * breaking the sched_group lists - i.e. a later get_group() pass
>  	 * breaks the linking done for an earlier span.
>  	 */
> -	for_each_cpu(i, cpu_map) {
> -		if (i == cpu)
> -			continue;
> +	for_each_cpu_from(i, cpu_map) {
>  		/*
>  		 * We should 'and' all those masks with 'cpu_map' to exactly
>  		 * match the topology we're about to build, but that can only
> -- 
> 2.44.0