[tip: sched/core] sched/numa: Stop an exhastive search if an idle core is found

[tip-bot2 for Hao Jia]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     feaed76376fd612b9450ad1251aec20a63ccfe92
Gitweb:        https://git.kernel.org/tip/feaed76376fd612b9450ad1251aec20a63ccfe92
Author:        Hao Jia <jiahao.os@xxxxxxxxxxxxx>
AuthorDate:    Fri, 16 Dec 2022 14:24:05 +08:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Tue, 27 Dec 2022 12:52:16 +01:00

sched/numa: Stop an exhastive search if an idle core is found

In update_numa_stats() we try to find an idle cpu on the NUMA node,
preferably an idle core. we can stop looking for the next idle core
or idle cpu after finding an idle core. But we can't stop the
whole loop of scanning the CPU, because we need to calculate
approximate NUMA stats at a point in time. For example,
the src and dst nr_running is needed by task_numa_find_cpu().

Signed-off-by: Hao Jia <jiahao.os@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20221216062406.7812-2-jiahao.os@xxxxxxxxxxxxx
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d0e2a48..aaff209 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1804,7 +1804,7 @@ static void update_numa_stats(struct task_numa_env *env,
 		ns->nr_running += rq->cfs.h_nr_running;
 		ns->compute_capacity += capacity_of(cpu);
 
-		if (find_idle && !rq->nr_running && idle_cpu(cpu)) {
+		if (find_idle && idle_core < 0 && !rq->nr_running && idle_cpu(cpu)) {
 			if (READ_ONCE(rq->numa_migrate_on) ||
 			    !cpumask_test_cpu(cpu, env->p->cpus_ptr))
 				continue;