sched/fair: Filter false overloaded_group case for EAS

With EAS, a group should be set overloaded if at least 1 CPU in the group
is overutilized but it can happen that a CPU is fully utilized by tasks
because of clamping the compute capacity of the CPU. In such case, the CPU
is not overutilized and as a result should not be set overloaded as well.

group_overloaded being a higher priority than group_misfit, such group can
be selected as the busiest group instead of a group with a mistfit task
and prevents load_balance to select the CPU with the misfit task to pull
the latter on a fitting CPU.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Pierre Gondois <pierre.gondois@arm.com>
Link: https://patch.msgid.link/20260206095454.1520619-1-vincent.guittot@linaro.org

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b8b052b2149b703afe74fae395bd22f8c499fe79..966e2528221549202260d8bec9625f093460b6b2 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10211,6 +10211,7 @@ struct sg_lb_stats {
        unsigned int group_asym_packing;        /* Tasks should be moved to preferred CPU */
        unsigned int group_smt_balance;         /* Task on busy SMT be moved */
        unsigned long group_misfit_task_load;   /* A CPU has a task too big for its capacity */
+       unsigned int group_overutilized;        /* At least one CPU is overutilized in the group */
 #ifdef CONFIG_NUMA_BALANCING
        unsigned int nr_numa_running;
        unsigned int nr_preferred_running;
@@ -10443,6 +10444,13 @@ group_has_capacity(unsigned int imbalance_pct, struct sg_lb_stats *sgs)
 static inline bool
 group_is_overloaded(unsigned int imbalance_pct, struct sg_lb_stats *sgs)
 {
+       /*
+        * With EAS and uclamp, 1 CPU in the group must be overutilized to
+        * consider the group overloaded.
+        */
+       if (sched_energy_enabled() && !sgs->group_overutilized)
+               return false;
+
        if (sgs->sum_nr_running <= sgs->group_weight)
                return false;
 
@@ -10626,14 +10634,12 @@ sched_reduced_capacity(struct rq *rq, struct sched_domain *sd)
  * @group: sched_group whose statistics are to be updated.
  * @sgs: variable to hold the statistics for this group.
  * @sg_overloaded: sched_group is overloaded
- * @sg_overutilized: sched_group is overutilized
  */
 static inline void update_sg_lb_stats(struct lb_env *env,
                                      struct sd_lb_stats *sds,
                                      struct sched_group *group,
                                      struct sg_lb_stats *sgs,
-                                     bool *sg_overloaded,
-                                     bool *sg_overutilized)
+                                     bool *sg_overloaded)
 {
        int i, nr_running, local_group, sd_flags = env->sd->flags;
        bool balancing_at_rd = !env->sd->parent;
@@ -10655,7 +10661,7 @@ static inline void update_sg_lb_stats(struct lb_env *env,
                sgs->sum_nr_running += nr_running;
 
                if (cpu_overutilized(i))
-                       *sg_overutilized = 1;
+                       sgs->group_overutilized = 1;
 
                /*
                 * No need to call idle_cpu() if nr_running is not 0
@@ -11326,13 +11332,15 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
                                update_group_capacity(env->sd, env->dst_cpu);
                }
 
-               update_sg_lb_stats(env, sds, sg, sgs, &sg_overloaded, &sg_overutilized);
+               update_sg_lb_stats(env, sds, sg, sgs, &sg_overloaded);
 
                if (!local_group && update_sd_pick_busiest(env, sds, sg, sgs)) {
                        sds->busiest = sg;
                        sds->busiest_stat = *sgs;
                }
 
+               sg_overutilized |= sgs->group_overutilized;
+
                /* Now, start updating sd_lb_stats */
                sds->total_load += sgs->group_load;
                sds->total_capacity += sgs->group_capacity;