diff options
| author | Ricardo Neri <ricardo.neri-calderon@linux.intel.com> | 2026-07-20 19:43:19 -0700 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2026-08-07 18:27:10 +0200 |
| commit | 50b101f6e586b4417d060a976fd831cd87e86e2b (patch) | |
| tree | a459c7b5d9892bccd96d3b04c82fcfcc011712bd /kernel | |
| parent | 6060d61d13a10da8c90da4eadf4a421825149883 (diff) | |
sched/fair: Check CPU capacity before comparing group types during load balance
update_sd_pick_busiest() may incorrectly select a fully_busy group as the
busiest group when its per-CPU capacity exceeds that of the destination
CPU. This happens because the type of busiest group is initialized to
group_has_spare and allows the fully_busy group to win the type comparison.
update_sd_pick_busiest() should not choose a candidate scheduling group
with at most one runnable task if its per-CPU capacity is greater than that
of the destination CPU. Such a check already exists, but it is done too
late: after the type comparison, preventing a subsequent fully_busy group
of equal per-CPU capacity from being correctly selected.
Move this check to occur before comparing group types.
Fixes: 0b0695f2b34a ("sched/fair: Rework load_balance()")
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Reviewed-by: Chen Yu <yu.c.chen@intel.com>
Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Tested-by: Christian Loehle <christian.loehle@arm.com>
Tested-by: Andrea Righi <arighi@nvidia.com>
Link: https://patch.msgid.link/20260720-rneri-fix-cas-clusters-v6-3-bb500bf4afd4@linux.intel.com
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/sched/fair.c | 22 |
1 files changed, 11 insertions, 11 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 2c5cfec73c76..f9d0edd6828d 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -12054,6 +12054,17 @@ static bool update_sd_pick_busiest(struct lb_env *env, sds->local_stat.group_type != group_has_spare)) return false; + /* + * Candidate sg has no more than one task per CPU and has higher + * per-CPU capacity. Migrating tasks to less capable CPUs may harm + * throughput. Maximize throughput, power/energy consequences are not + * considered. + */ + if ((env->sd->flags & SD_ASYM_CPUCAPACITY) && + (sgs->group_type <= group_fully_busy) && + (capacity_greater(sg->sgc->min_capacity, capacity_of(env->dst_cpu)))) + return false; + if (sgs->group_type > busiest->group_type) return true; @@ -12160,17 +12171,6 @@ has_spare: break; } - /* - * Candidate sg has no more than one task per CPU and has higher - * per-CPU capacity. Migrating tasks to less capable CPUs may harm - * throughput. Maximize throughput, power/energy consequences are not - * considered. - */ - if ((env->sd->flags & SD_ASYM_CPUCAPACITY) && - (sgs->group_type <= group_fully_busy) && - (capacity_greater(sg->sgc->min_capacity, capacity_of(env->dst_cpu)))) - return false; - return true; } |