[tip: sched/core] sched/fair: Do not compute overloaded status unnecessarily during lb

[tip-bot2 for K Prateek Nayak]

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

Commit-ID:     3229adbe787534b43430f92e10175c9b77f2d27c
Gitweb:        https://git.kernel.org/tip/3229adbe787534b43430f92e10175c9b77f2d27c
Author:        K Prateek Nayak <kprateek.nayak@xxxxxxx>
AuthorDate:    Mon, 23 Dec 2024 04:34:06 
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Mon, 13 Jan 2025 14:10:25 +01:00

sched/fair: Do not compute overloaded status unnecessarily during lb

Only set sg_overloaded when computing sg_lb_stats() at the highest sched
domain since rd->overloaded status is updated only when load balancing
at the highest domain. While at it, move setting of sg_overloaded below
idle_cpu() check since an idle CPU can never be overloaded.

Signed-off-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Reviewed-by: Shrikanth Hegde <sshegde@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20241223043407.1611-8-kprateek.nayak@xxxxxxx
---
 kernel/sched/fair.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 650d698..98ac49c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10410,6 +10410,7 @@ static inline void update_sg_lb_stats(struct lb_env *env,
 				      bool *sg_overutilized)
 {
 	int i, nr_running, local_group, sd_flags = env->sd->flags;
+	bool balancing_at_rd = !env->sd->parent;
 
 	memset(sgs, 0, sizeof(*sgs));
 
@@ -10427,9 +10428,6 @@ static inline void update_sg_lb_stats(struct lb_env *env,
 		nr_running = rq->nr_running;
 		sgs->sum_nr_running += nr_running;
 
-		if (nr_running > 1)
-			*sg_overloaded = 1;
-
 		if (cpu_overutilized(i))
 			*sg_overutilized = 1;
 
@@ -10442,6 +10440,10 @@ static inline void update_sg_lb_stats(struct lb_env *env,
 			continue;
 		}
 
+		/* Overload indicator is only updated at root domain */
+		if (balancing_at_rd && nr_running > 1)
+			*sg_overloaded = 1;
+
 #ifdef CONFIG_NUMA_BALANCING
 		/* Only fbq_classify_group() uses this to classify NUMA groups */
 		if (sd_flags & SD_NUMA) {