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SubjectRe: [PATCH 8/9] sched/fair: select idle cpu from idle cpumask for task wakeup
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> @@ -4965,6 +4965,7 @@ void scheduler_tick(void)
>
> #ifdef CONFIG_SMP
> rq->idle_balance = idle_cpu(cpu);
> + update_idle_cpumask(cpu, rq->idle_balance);
> trigger_load_balance(rq);
> #endif
> }

might be stupid, a question bothering yicong and me is that why don't we
choose to update_idle_cpumask() while idle task exits and switches to a
normal task?
for example, before tick comes, cpu has exited from idle, but we are only
able to update it in tick. this makes idle_cpus_span inaccurate, thus we
will scan cpu which isn't actually idle in select_idle_sibling.
is it because of the huge update overhead?

Thanks
barry

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