Messages in this thread | | | Date | Thu, 8 Oct 2015 20:05:57 +0200 | From | Oleg Nesterov <> | Subject | Re: [RFC][PATCH] sched: Start stopper early |
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To avoid the confusion, let me repeat that I am not arguing with this change, perhaps it makes sense too.
But unless I missed something it is not really correct and can't fix the problem. So I still think the series I sent should be applied first.
On 10/07, Peter Zijlstra wrote: > static int sched_cpu_active(struct notifier_block *nfb, > unsigned long action, void *hcpu) > { > + int cpu = (long)hcpu; > + > switch (action & ~CPU_TASKS_FROZEN) { > case CPU_STARTING: > set_cpu_rq_start_time(); > return NOTIFY_OK; > case CPU_ONLINE: > + cpu_stopper_unpark(cpu); > /* > * At this point a starting CPU has marked itself as online via > * set_cpu_online(). But it might not yet have marked itself > @@ -5558,7 +5563,7 @@ static int sched_cpu_active(struct notifier_block *nfb, > * Thus, fall-through and help the starting CPU along. > */ > case CPU_DOWN_FAILED: > - set_cpu_active((long)hcpu, true); > + set_cpu_active(cpu, true); > return NOTIFY_OK; > default: > return NOTIFY_DONE; > diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c > index 12484e5..c674371 100644 > --- a/kernel/stop_machine.c > +++ b/kernel/stop_machine.c > @@ -496,6 +496,11 @@ static struct smp_hotplug_thread cpu_stop_threads = { > .selfparking = true, > }; > > +void cpu_stopper_unpark(unsigned int cpu) > +{ > + kthread_unpark(per_cpu(cpu_stopper.thread, cpu)); > +}
But note that kthread_unpark() will only wake the stopper thread up.
cpu_stopper->enabled is still false, and it will be false until smpboot_unpark_thread() calls ->pre_unpark() later. And this means that stop_two_cpus()->cpu_stop_queue_work() can silently fail until then. So I don't this patch can fix the problem.
Oleg.
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