Re: [PATCH 15/16] sched/topology: optimize topology_span_sane()

Peter Zijlstra
2022-07-18T21:38:42Z

On Mon, Jul 18, 2022 at 12:28:43PM -0700, Yury Norov wrote:

> kernel/sched/topology.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index 05b6c2ad90b9..ad32d0a43424 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -2211,6 +2211,8 @@ 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)
> {
> + const struct cpumask *mc = tl->mask(cpu);
> + const struct cpumask *mi;
> int i;
>
> /* NUMA levels are allowed to overlap */
> @@ -2226,14 +2228,18 @@ static bool topology_span_sane(struct sched_domain_topology_level *tl,
> for_each_cpu(i, cpu_map) {
> if (i == cpu)
> continue;
> +
> + mi = tl->mask(i);
> + if (mi == mc)
> + continue;
> +
> /*
> * We should 'and' all those masks with 'cpu_map' to exactly
> * match the topology we're about to build, but that can only
> * remove CPUs, which only lessens our ability to detect
> * overlaps
> */
> - if (!cpumask_equal(tl->mask(cpu), tl->mask(i)) &&
> - cpumask_intersects(tl->mask(cpu), tl->mask(i)))
> + if (!cpumask_equal(mc, mi) && cpumask_intersects(mc, mi))
> return false;
> }

This is once again a super slow path; but I don't suppose you're making
the code worse in this case.