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sched/fair: Use READ_ONCE() to read sg->asym_prefer_cpu

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Subsequent commits add the support to dynamically update the sched_group
struct's "asym_prefer_cpu" member from a remote CPU. Use READ_ONCE()
when reading the "sg->asym_prefer_cpu" to ensure load balancer always
reads the latest value.

Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250409053446.23367-2-kprateek.nayak@amd.com
This commit is contained in:
K Prateek Nayak 2025-04-09 05:34:43 +00:00 committed by Peter Zijlstra
parent 6432e163ba
commit 872aa4de18
1 changed files with 3 additions and 2 deletions
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5
kernel/sched/fair.c
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@ -10251,7 +10251,7 @@ sched_group_asym(struct lb_env *env, struct sg_lb_stats *sgs, struct sched_group
(sgs->group_weight - sgs->idle_cpus != 1))
return false;
return sched_asym(env->sd, env->dst_cpu, group->asym_prefer_cpu);
return sched_asym(env->sd, env->dst_cpu, READ_ONCE(group->asym_prefer_cpu));
}
/* One group has more than one SMT CPU while the other group does not */
@ -10488,7 +10488,8 @@ static bool update_sd_pick_busiest(struct lb_env *env,
case group_asym_packing:
/* Prefer to move from lowest priority CPU's work */
return sched_asym_prefer(sds->busiest->asym_prefer_cpu, sg->asym_prefer_cpu);
return sched_asym_prefer(READ_ONCE(sds->busiest->asym_prefer_cpu),
READ_ONCE(sg->asym_prefer_cpu));
case group_misfit_task:
/*