diff options
| author | Andrea Righi <arighi@nvidia.com> | 2026-05-09 20:07:28 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2026-05-19 12:17:38 +0200 |
| commit | bf6aa722198d3c06e4236e8c5a480f30a64e1513 (patch) | |
| tree | 3cd0614cf1219f00de3ac990f84612630424b943 | |
| parent | 25a32e400a14009601c0a727643057f5515152df (diff) | |
sched/fair: Reject misfit pulls onto busy SMT siblings on asym-capacity
When SD_ASYM_CPUCAPACITY load balancing considers pulling a misfit task,
capacity_of(dst_cpu) can overstate available compute if the SMT sibling is
busy: the core does not deliver its full nominal capacity.
If SMT is active and dst_cpu is not on a fully idle core, skip this
destination so we do not migrate a misfit expecting a capacity upgrade we
cannot actually provide.
Reported-by: Felix Abecassis <fabecassis@nvidia.com>
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://patch.msgid.link/20260509180955.1840064-5-arighi@nvidia.com
| -rw-r--r-- | kernel/sched/fair.c | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 8854d4d980b0..f69ee5ae2b8c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -9625,6 +9625,7 @@ struct lb_env { int dst_cpu; struct rq *dst_rq; + bool dst_core_idle; struct cpumask *dst_grpmask; int new_dst_cpu; @@ -10850,10 +10851,16 @@ static bool update_sd_pick_busiest(struct lb_env *env, * We can use max_capacity here as reduction in capacity on some * CPUs in the group should either be possible to resolve * internally or be covered by avg_load imbalance (eventually). + * + * When SMT is active, only pull a misfit to dst_cpu if it is on a + * fully idle core; otherwise the effective capacity of the core is + * reduced and we may not actually provide more capacity than the + * source. */ if ((env->sd->flags & SD_ASYM_CPUCAPACITY) && (sgs->group_type == group_misfit_task) && - (!capacity_greater(capacity_of(env->dst_cpu), sg->sgc->max_capacity) || + (!env->dst_core_idle || + !capacity_greater(capacity_of(env->dst_cpu), sg->sgc->max_capacity) || sds->local_stat.group_type != group_has_spare)) return false; @@ -11417,6 +11424,8 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd unsigned long sum_util = 0; bool sg_overloaded = 0, sg_overutilized = 0; + env->dst_core_idle = !sched_smt_active() || is_core_idle(env->dst_cpu); + do { struct sg_lb_stats *sgs = &tmp_sgs; int local_group; |