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 <[email protected]>
Reviewed-by: Yury Norov <[email protected]>
> ---
> 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