Commit ce29a7da authored by Steve Wahl's avatar Steve Wahl Committed by Peter Zijlstra
Browse files

sched/topology: Refinement to topology_span_sane speedup 



Simplify the topology_span_sane code further, removing the need to
allocate an array and gotos used to make sure the array gets freed.

This version is in a separate commit because it could return a
different sanity result than the previous code, but only in odd
circumstances that are not expected to actually occur; for example,
when a CPU is not listed in its own mask.

Signed-off-by: default avatarSteve Wahl <steve.wahl@hpe.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarValentin Schneider <vschneid@redhat.com>
Reviewed-by: default avatarMadadi Vineeth Reddy <vineethr@linux.ibm.com>
Tested-by: default avatarK Prateek Nayak <kprateek.nayak@amd.com>
Tested-by: default avatarValentin Schneider <vschneid@redhat.com>
Tested-by: default avatarMadadi Vineeth Reddy <vineethr@linux.ibm.com>
Link: https://lore.kernel.org/r/20250304160844.75373-3-steve.wahl@hpe.com
parent f55dac1d

kernel/sched/topology.c

+19 −33
Original line number Diff line number Diff line
@@ -2352,17 +2352,12 @@ static struct sched_domain *build_sched_domain(struct sched_domain_topology_leve 
static bool topology_span_sane(const struct cpumask *cpu_map)

{

	struct sched_domain_topology_level *tl;

	const struct cpumask **masks;

	struct cpumask *covered;

	int cpu, id;

	bool ret = false;

	struct cpumask *covered, *id_seen;

	int cpu;



	lockdep_assert_held(&sched_domains_mutex);

	covered = sched_domains_tmpmask;



	masks = kmalloc_array(nr_cpu_ids, sizeof(struct cpumask *), GFP_KERNEL);

	if (!masks)

		return ret;

	id_seen = sched_domains_tmpmask2;



	for_each_sd_topology(tl) {
@@ -2371,7 +2366,7 @@ static bool topology_span_sane(const struct cpumask *cpu_map) 
			continue;



		cpumask_clear(covered);

		memset(masks, 0, nr_cpu_ids * sizeof(struct cpumask *));

		cpumask_clear(id_seen);



		/*

		 * Non-NUMA levels cannot partially overlap - they must be either
@@ -2380,36 +2375,27 @@ static bool topology_span_sane(const struct cpumask *cpu_map) 
		 * breaks the linking done for an earlier span.

		 */

		for_each_cpu(cpu, cpu_map) {

			/* lowest bit set in this mask is used as a unique id */

			id = cpumask_first(tl->mask(cpu));

			const struct cpumask *tl_cpu_mask = tl->mask(cpu);

			int id;



			/* zeroed masks cannot possibly collide */

			if (id >= nr_cpu_ids)

				continue;

			/* lowest bit set in this mask is used as a unique id */

			id = cpumask_first(tl_cpu_mask);



			/* if this mask doesn't collide with what we've already seen */

			if (!cpumask_intersects(tl->mask(cpu), covered)) {

				/* this failing would be an error in this algorithm */

				if (WARN_ON(masks[id]))

					goto notsane;

			if (cpumask_test_cpu(id, id_seen)) {

				/* First CPU has already been seen, ensure identical spans */

				if (!cpumask_equal(tl->mask(id), tl_cpu_mask))

					return false;

			} else {

				/* First CPU hasn't been seen before, ensure it's a completely new span */

				if (cpumask_intersects(tl_cpu_mask, covered))

					return false;



				/* record the mask we saw for this id */

				masks[id] = tl->mask(cpu);

				cpumask_or(covered, tl->mask(cpu), covered);

			} else if ((!masks[id]) || !cpumask_equal(masks[id], tl->mask(cpu))) {

				/*

				 * a collision with covered should have exactly matched

				 * a previously seen mask with the same id

				 */

				goto notsane;

				cpumask_or(covered, covered, tl_cpu_mask);

				cpumask_set_cpu(id, id_seen);

			}

		}

	}

	ret = true;



 notsane:

	kfree(masks);

	return ret;

	return true;

}



/*