Messages in this thread | | | Date | Thu, 10 Dec 2020 19:24:25 -0800 | From | "Paul E. McKenney" <> | Subject | Re: NOHZ tick-stop error: Non-RCU local softirq work is pending |
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On Fri, Dec 11, 2020 at 02:40:31AM +0100, Frederic Weisbecker wrote: > On Thu, Dec 10, 2020 at 04:46:38PM -0800, Paul E. McKenney wrote: > > > diff --git a/kernel/softirq.c b/kernel/softirq.c > > > index 09229ad82209..7d558cb7a037 100644 > > > --- a/kernel/softirq.c > > > +++ b/kernel/softirq.c > > > @@ -650,7 +650,9 @@ static void run_ksoftirqd(unsigned int cpu) > > > * We can safely run softirq on inline stack, as we are not deep > > > * in the task stack here. > > > */ > > > - __do_softirq(); > > > + do { > > > + __do_softirq(); > > > + } while (kthread_should_park() && local_softirq_pending()); > > > local_irq_enable(); > > > cond_resched(); > > > return; > > > > Huh. I guess that self-propagating timers, RCU callbacks, and the > > like are non-problems because they cannot retrigger while interrupts > > are disabled? But can these things reappear just after the > > local_irq_enable()? > > Exactly, unless those things have been disabled in CPU hotplug callbacks > before smpboot_park_threads() (and we are not too deep in CPU hotplug at that > stage, cpu_online() is still true), they should be able to raise again > the softirqs. Yeah I'm pretty sure the above won't be enough. > > > In the case of RCU, softirq would need to run on this CPU, which it won't, > > so we are good in that case. (Any stranded callbacks will be requeued > > onto some other CPU later in the CPU-hotplug offline processing.) > > Ah that's good, so at least we shouldn't worry about pending RCU softirqs > after ksoftirqd has parked. But I also see at least SCHED_SOFTIRQ and > TIMER_SOFTIRQ in your list. > > Perhaps we should have some flush_softirq() somewhere late in cpu hotplug, > assuming this is actually necessary and none of these will requeue themselves...
Indeed, let's see if we have a problem before we worry too much about fixing it. ;-)
I still get the "NOHZ tick-stop error", but more than three times less often, so definite improvement. One of the console.log file is attached.
Thanx, Paul [unhandled content-type:application/gzip] | |