Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1334754

Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace timers with utilization ...'

Show all headers | View raw

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.

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Crashes in arm qemu emulations due to 'cpufreq: governor: Replace  timers with utilization ...' Guenter Roeck <linux@roeck-us.net> - 2016-02-15 18:10 +0100
  Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace  timers with utilization ...' "Rafael J. Wysocki" <rafael@kernel.org> - 2016-02-15 19:50 +0100
    Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace  timers with utilization ...' "Rafael J. Wysocki" <rafael@kernel.org> - 2016-02-15 19:50 +0100
    Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace  timers with utilization ...' Marc Zyngier <marc.zyngier@arm.com> - 2016-02-15 20:00 +0100
      Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace  timers with utilization ...' "Rafael J. Wysocki" <rafael@kernel.org> - 2016-02-15 20:00 +0100
        Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace  timers with utilization ...' Marc Zyngier <marc.zyngier@arm.com> - 2016-02-15 20:10 +0100
          Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace  timers with utilization ...' "Rafael J. Wysocki" <rafael@kernel.org> - 2016-02-15 20:20 +0100
            Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace timers with utilization ...' "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-02-15 20:30 +0100
              Re: Crashes in arm qemu emulations due to 'cpufreq: governor:  Replace timers with utilization ...' Guenter Roeck <linux@roeck-us.net> - 2016-02-15 20:50 +0100
                Re: Crashes in arm qemu emulations due to 'cpufreq: governor:  Replace timers with utilization ...' Tony Lindgren <tony@atomide.com> - 2016-02-15 21:00 +0100
              Re: Crashes in arm qemu emulations due to 'cpufreq: governor:  Replace timers with utilization ...' Tony Lindgren <tony@atomide.com> - 2016-02-15 20:50 +0100
          Re: Crashes in arm qemu emulations due to 'cpufreq: governor:  Replace timers with utilization ...' Russell King - ARM Linux <linux@arm.linux.org.uk> - 2016-02-15 20:30 +0100
            Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace  timers with utilization ...' "Rafael J. Wysocki" <rafael@kernel.org> - 2016-02-15 21:50 +0100
        Re: Crashes in arm qemu emulations due to 'cpufreq: governor:  Replace timers with utilization ...' Russell King - ARM Linux <linux@arm.linux.org.uk> - 2016-02-15 20:10 +0100
    Re: Crashes in arm qemu emulations due to 'cpufreq: governor:  Replace timers with utilization ...' Russell King - ARM Linux <linux@arm.linux.org.uk> - 2016-02-15 20:10 +0100
    Re: Crashes in arm qemu emulations due to 'cpufreq: governor:  Replace timers with utilization ...' Tony Lindgren <tony@atomide.com> - 2016-02-15 20:10 +0100
      Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace  timers with utilization ...' Guenter Roeck <linux@roeck-us.net> - 2016-02-15 20:50 +0100
        Re: Crashes in arm qemu emulations due to 'cpufreq: governor:  Replace timers with utilization ...' Tony Lindgren <tony@atomide.com> - 2016-02-15 21:00 +0100
          Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace  timers with utilization ...' Guenter Roeck <linux@roeck-us.net> - 2016-02-15 21:10 +0100
            Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace  timers with utilization ...' "Rafael J. Wysocki" <rafael@kernel.org> - 2016-02-15 21:40 +0100
          Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace  timers with utilization ...' "Rafael J. Wysocki" <rafael@kernel.org> - 2016-02-15 21:40 +0100
            Re: Crashes in arm qemu emulations due to 'cpufreq: governor:  Replace timers with utilization ...' Tony Lindgren <tony@atomide.com> - 2016-02-15 22:40 +0100
              Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace  timers with utilization ...' Guenter Roeck <linux@roeck-us.net> - 2016-02-16 02:40 +0100
    Re: Crashes in arm qemu emulations due to 'cpufreq: governor:  Replace timers with utilization ...' Viresh Kumar <viresh.kumar@linaro.org> - 2016-02-16 02:20 +0100
      Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace timers with utilization ...' "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-02-16 02:30 +0100
        Re: Crashes in arm qemu emulations due to 'cpufreq: governor:  Replace timers with utilization ...' Viresh Kumar <viresh.kumar@linaro.org> - 2016-02-16 02:40 +0100
  Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace  timers with utilization ...' Peter Maydell <peter.maydell@linaro.org> - 2016-02-15 23:40 +0100
    Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace  timers with utilization ...' Guenter Roeck <linux@roeck-us.net> - 2016-02-16 00:30 +0100

csiph-web