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SubjectRe: [PATCH 3/6] x86_64 UV: Use blinking LED for heartbeat display
> 
> * Mike Travis <travis@sgi.com> wrote:
>
> > +#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
> > +static void uv_display_heartbeat(void)
> > +{
> > + int cpu;
> > +
> > + uv_hub_info->led_heartbeat_count = nr_cpu_ids;
> > +
> > + for_each_online_cpu(cpu) {
> > + struct uv_hub_info_s *hub = uv_cpu_hub_info(cpu);
> > +
> > + if (hub->led_heartbeat_count > 0) {
> > + uv_set_led_bits_on(cpu, LED_CPU_BLINK,
> > + LED_CPU_HEARTBEAT);
> > + --hub->led_heartbeat_count;
> > + }
>
> this too is a bad idea. Imagine 16K cores and assume that each such
> iteration takes a few usecs (we write cross CPU) and you've got a
> GHz-ish CPU. That can easily be _milliseconds_ of delay (or more) - and
> in a function (the clocksource watchdog) that is all about precise
> timings.
>
> It is also very non-preemptable.

LED subsystem already has nice heartbeat trigger.
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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