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SubjectRe: [PATCH] watchdog: touch_nmi_watchdog should only touch local cpu not every one
On Fri, 5 Nov 2010 15:51:18 +0200
Sergey Senozhatsky <sergey.senozhatsky@gmail.com> wrote:

> On (11/04/10 21:18), Don Zickus wrote:
> > void touch_nmi_watchdog(void)
> > {
> > + /*
> > + * Using __raw here because some code paths have
> > + * preemption enabled. If preemption is enabled
> > + * then interrupts should be enabled too, in which
> > + * case we shouldn't have to worry about the watchdog
> > + * going off.
> > + */
> > + __raw_get_cpu_var(watchdog_nmi_touch) = true;
> > +
> > + touch_softlockup_watchdog();
> > +}
> > +EXPORT_SYMBOL(touch_nmi_watchdog);
> > +
> > +void touch_all_nmi_watchdogs(void)
> > +{
> > if (watchdog_enabled) {
> > unsigned cpu;
> >
> > @@ -151,7 +166,7 @@ void touch_nmi_watchdog(void)
> > }
> > touch_softlockup_watchdog();
> > }
> > -EXPORT_SYMBOL(touch_nmi_watchdog);
> > +EXPORT_SYMBOL(touch_all_nmi_watchdogs);
> >
>
> Hello,
> Seems like no one is actually calling touch_all_nmi_watchdogs, as for now.
> Right?

Yes, there doesn't seem a lot of point in adding the interface unless
we have callers.

>
> Minor nit
>
> touch_all_nmi_watchdogs:
> ...
> for_each_present_cpu(cpu) {
> if (per_cpu(watchdog_nmi_touch, cpu) != true)
> per_cpu(watchdog_nmi_touch, cpu) = true;
> }
>
>
> which is, I belive, could be simplified to
> for_each_present_cpu(cpu) {
> per_cpu(watchdog_nmi_touch, cpu) = true;
> }

We sometimes do this trick to avoid dirtying lots of cachelines which
already held the correct value. It'll be extra-benefical when dealing
with other CPU's data, I expect.


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