Commit 05037e5f authored by Kyle Meyer's avatar Kyle Meyer Committed by Yury Norov
Browse files

sched/topology: Optimize topology_span_sane() 



Optimize topology_span_sane() by removing duplicate comparisons.

Since topology_span_sane() is called inside of for_each_cpu(), each
previous CPU has already been compared against every other CPU. The
current CPU only needs to be compared against higher-numbered CPUs.

The total number of comparisons is reduced from N * (N - 1) to
N * (N - 1) / 2 on each non-NUMA scheduling domain level.

Signed-off-by: default avatarKyle Meyer <kyle.meyer@hpe.com>
Reviewed-by: default avatarYury Norov <yury.norov@gmail.com>
Acked-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: default avatarYury Norov <yury.norov@gmail.com>
parent 6802f934

kernel/sched/topology.c

+2 −4
Original line number Diff line number Diff line
@@ -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