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sched/fair: Filter false overloaded_group case for EAS

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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
This commit is contained in:
Vincent Guittot 2026-02-06 10:54:54 +01:00 committed by Peter Zijlstra
parent 9264758066
commit d3d663faa1
1 changed files with 13 additions and 5 deletions
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18
kernel/sched/fair.c
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@ -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;