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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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