On 4/4/19 3:03 PM, Peter Zijlstra wrote: > On Thu, Apr 04, 2019 at 01:09:09PM +0200, Peter Zijlstra wrote: > >> That is not entirely the scenario I talked about, but *groan*. >> >> So what I meant was: >> >> CPU-0 CPU-n >> >> __schedule() >> local_irq_disable() >> >> ... >> deactivate_task(prev); >> >> >> try_to_wake_up(@p) >> ... >> >> smp_cond_load_acquire(&p->on_cpu, !VAL); >> >> <PMI> >> .. >> perf_event_disable_inatomic() >> event->pending_disable = 1; >> irq_work_queue() /* self-IPI */ >> </PMI> >> >> context_switch() >> prepare_task_switch() >> perf_event_task_sched_out() >> // the above chain that clears pending_disable >> >> finish_task_switch() >> finish_task() >> smp_store_release(prev->on_cpu, 0); >> /* >> finally.... */ >> // take woken >> // >> context_switch to @p >> finish_lock_switch() >> raw_spin_unlock_irq() >> /* w00t, IRQs enabled, self-IPI time */ >> <self-IPI> >> perf_pending_event() >> // event->pending_disable == 0 >> </self-IPI> >> >> >> What you're suggesting, is that the time between: >> >> smp_store_release(prev->on_cpu, 0); >> >> and >> >> <self-IPI> >> >> on CPU-0 is sufficient for CPU-n to context switch to the task, enable >> the event there, trigger a PMI that calls perf_event_disable_inatomic() >> _again_ (this would mean irq_work_queue() failing, which we don't check) >> (and schedule out again, although that's not required). >> >> This being virt that might actually be possible if (v)CPU-0 takes a nap >> I suppose. >> >> Let me think about this a little more... > > Does the below cure things? It's not exactly pretty, but it could just > do the trick. >
Thanks a lot for the patch, I have built a new kernel and let it run over the week end. s390 does not have a PMI, all interrupts (including the measurement interrupts from the PMU) are normal, maskable interrupts. -- Thomas Richter, Dept 3252, IBM s390 Linux Development, Boeblingen, Germany -- Vorsitzender des Aufsichtsrats: Matthias Hartmann Geschäftsführung: Dirk Wittkopp Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294
