Messages in this thread | | | Date | Mon, 15 Feb 2016 19:23:17 +0000 | From | Russell King - ARM Linux <> | Subject | Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace timers with utilization ...' |
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On Mon, Feb 15, 2016 at 07:03:33PM +0000, Marc Zyngier wrote: > On 15/02/16 18:54, Rafael J. Wysocki wrote: > > That would explain it, thanks. > > > > So it looks like we should always use irq_work_queue() on UP even if > > CONFIG_SMP is set, shouldn't we? > > Something like that, yes. CONFIG_SMP is not an indication of an SMP > system anymore (we've even dropped the config option on arm64). > > Hopefully num_possible_cpus() is reliable enough to let you do the right > thing...
CONFIG_SMP just says whether to include support for SMP. It doesn't mandate running on a SMP system. :)
I've been looking around the usages of irq_work_queue_on in kernel/ in -rc4, and some places seem to check for "this CPU":
/* * It is possible that a restart caused this CPU to be * chosen again. Don't bother with an IPI, just see if we * have more to push. */ if (unlikely(cpu == rq->cpu)) goto again;
/* Try the next RT overloaded CPU */ irq_work_queue_on(&rt_rq->push_work, cpu);
I'm not sure about tell_cpu_to_push().
It's also called via tick_nohz_full_kick_cpu(), and the core scheduler avoids calling this for the current CPU:
if (tick_nohz_full_cpu(cpu)) { if (cpu != smp_processor_id() || tick_nohz_tick_stopped()) tick_nohz_full_kick_cpu(cpu);
I'm not sure about add_nr_running() in kernel/sched/sched.h - I think that _could_ be a problem even without Rafael's cpufreq change.
So... the question is what do we do with irq_work_queue_on() in general when called on non-SMP systems.
-- RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.
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