On Mon, 14 Jan 2013 16:19:23 -0800
Colin Cross <ccr...@android.com> wrote:
> >> +static void watchdog_check_hardlockup_other_cpu(void)
> >> +{
> >> + unsigned int next_cpu;
> >> +
> >> + /*
> >> + * Test for hardlockups every 3 samples. The sample period is
> >> + * watchdog_thresh * 2 / 5, so 3 samples gets us back to slightly
> >> over
> >> + * watchdog_thresh (over by 20%).
> >> + */
> >> + if (__this_cpu_read(hrtimer_interrupts) % 3 != 0)
> >> + return;
> >
> > The hardwired interval Seems Wrong. watchdog_thresh is tunable at runtime.
> >
> > The comment could do with some fleshing out. *why* do we want to test
> > at an interval "slightly over watchdog_thresh"? What's going on here?
>
> I'll reword it. We don't want to be slightly over watchdog_thresh,
> ideally we would be exactly at watchdog_thresh. However, since this
> relies on the hrtimer interrupts that are scheduled at watchdog_thresh
> * 2 / 5, there is no multiple of hrtimer_interrupts that will result
> in watchdog_thresh. watchdog_thresh * 2 / 5 * 3 (watchdog_thresh *
> 1.2) is the closest I can get to testing for a hardlockup once every
> watchdog_thresh seconds.
It needs more than rewording, doesn't it? What happens if watchdog_thresh is
altered at runtime?
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