Messages in this thread | | | Date | Tue, 31 Mar 2015 09:25:02 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] watchdog: nohz: don't run watchdog on nohz_full cores |
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* cmetcalf@ezchip.com <cmetcalf@ezchip.com> wrote:
> From: Chris Metcalf <cmetcalf@ezchip.com> > > Running watchdog can be a helpful debugging feature on regular > cores, but it's incompatible with nohz_full, since it forces > regular scheduling events. Accordingly, just exit out immediately > from any nohz_full core. > > An alternate approach would be to add a flags field or function to > smp_hotplug_thread to control on which cores the percpu threads > are created, but it wasn't clear that much mechanism was useful. > > Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com> > --- > kernel/watchdog.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/kernel/watchdog.c b/kernel/watchdog.c > index 3174bf8e3538..8a46d9d8a66f 100644 > --- a/kernel/watchdog.c > +++ b/kernel/watchdog.c > @@ -19,6 +19,7 @@ > #include <linux/sysctl.h> > #include <linux/smpboot.h> > #include <linux/sched/rt.h> > +#include <linux/tick.h> > > #include <asm/irq_regs.h> > #include <linux/kvm_para.h> > @@ -431,6 +432,10 @@ static void watchdog_enable(unsigned int cpu) > hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); > hrtimer->function = watchdog_timer_fn; > > + /* nohz_full cpus do not do watchdog checking. */ > + if (tick_nohz_full_cpu(cpu)) > + do_exit(0); > + > /* Enable the perf event */ > watchdog_nmi_enable(cpu);
So what happens if someone wants to enable the lockup detector, with a long timeout, even on nohz-full CPUs? This patch makes that impossible.
A better solution would be to tweak the defaults:
- to default the watchdog(s) to disabled when nohz-full is enabled, even if HARDLOCKUP_DETECTOR=y or DETECT_HUNG_TASK=y, and allow it to be re-enabled via its sysctl.
Thanks,
Ingo
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