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@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://lore.kernel.org/r/20241223043407.1611-8-kprateek.nayak@amd.com

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 650d698244c473fddfd0dfddd25c0a68811dde66..98ac49ce78ea876d56a58205510a320c0abf63f6 100644 (file)
--- 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) {