Peter Zijlstra <pet...@infradead.org> writes: > @@ -7883,14 +7889,6 @@ int sched_cpu_deactivate(unsigned int cp > set_cpu_active(cpu, false); > > /* > - * From this point forward, this CPU will refuse to run any task that > - * is not: migrate_disable() or KTHREAD_IS_PER_CPU, and will actively > - * push those tasks away until this gets cleared, see > - * sched_cpu_dying(). > - */ > - balance_push_set(cpu, true); > - > - /* > * We've cleared cpu_active_mask / set balance_push, wait for all > * preempt-disabled and RCU users of this state to go away such that > * all new such users will observe it. > @@ -7910,6 +7908,14 @@ int sched_cpu_deactivate(unsigned int cp > } > rq_unlock_irqrestore(rq, &rf); > > + /* > + * From this point forward, this CPU will refuse to run any task that > + * is not: migrate_disable() or KTHREAD_IS_PER_CPU, and will actively > + * push those tasks away until this gets cleared, see > + * sched_cpu_dying(). > + */ > + balance_push_set(cpu, true); > +
AIUI with cpu_dying_mask being flipped before even entering sched_cpu_deactivate(), we don't need this to be before the synchronize_rcu() anymore; is there more than that to why you're punting it back this side of it? > #ifdef CONFIG_SCHED_SMT > /* > * When going down, decrement the number of cores with SMT present. > @@ -8206,7 +8212,7 @@ void __init sched_init(void) > rq->sd = NULL; > rq->rd = NULL; > rq->cpu_capacity = rq->cpu_capacity_orig = SCHED_CAPACITY_SCALE; > - rq->balance_callback = NULL; > + rq->balance_callback = &balance_push_callback; > rq->active_balance = 0; > rq->next_balance = jiffies; > rq->push_cpu = 0; > @@ -8253,6 +8259,7 @@ void __init sched_init(void) > > #ifdef CONFIG_SMP > idle_thread_set_boot_cpu(); > + balance_push_set(smp_processor_id(), false); > #endif > init_sched_fair_class(); > I don't get what these two changes do - the end result is the same as before, no? Also, AIUI this patch covers the cpu_dying -> !cpu_dying rollback case since balance_push gets numbed down by !cpu_dying. What about the other way around (hot-plug failure + rollback)? We may have allowed !pcpu tasks on the now-dying CPU, and we'd need to re-install the balance_push callback. I'm starting to think we'd need to have rq->balance_callback = &balance_push_callback for any CPU with hotplug state < CPUHP_AP_ACTIVE. Thus we would need: balance_push_set(cpu, true) in sched_init() and sched_cpu_deactivate() balance_push_set(cpu, false) in sched_cpu_activate() and the rest would be driven by the cpu_dying_mask.
