[PATCH v3 4/7] lib/group_cpus: optimize outer loop in grp_spread_init_one()

Yury Norov
2023-12-12T04:21:31Z

Similarly to the inner loop, in the outer loop we can use for_each_cpu()
macro, and skip CPUs that have been copied.

With this patch, the function becomes O(1), despite that it's a
double-loop.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
---
lib/group_cpus.c | 12 ++++--------
1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/lib/group_cpus.c b/lib/group_cpus.c
index 7ac94664230f..cded3c8ea63b 100644
--- a/lib/group_cpus.c
+++ b/lib/group_cpus.c
@@ -17,16 +17,11 @@ static void grp_spread_init_one(struct cpumask *irqmsk, struct cpumask *nmsk,
const struct cpumask *siblmsk;
int cpu, sibl;

- for ( ; cpus_per_grp > 0; ) {
- cpu = cpumask_first(nmsk);
-
- /* Should not happen, but I'm too lazy to think about it */
- if (cpu >= nr_cpu_ids)
- return;
-
+ for_each_cpu(cpu, nmsk) {
__cpumask_clear_cpu(cpu, nmsk);
__cpumask_set_cpu(cpu, irqmsk);
- cpus_per_grp--;
+ if (cpus_per_grp-- == 0)
+ return;

/* If the cpu has siblings, use them first */
siblmsk = topology_sibling_cpumask(cpu);
@@ -37,6 +32,7 @@ static void grp_spread_init_one(struct cpumask *irqmsk, struct cpumask *nmsk,
__cpumask_set_cpu(sibl, irqmsk);
if (cpus_per_grp-- == 0)
return;
+ cpu = sibl + 1;
}
}
}
--
2.40.1