Messages in this thread | | | Date | Wed, 13 Aug 2008 11:57:15 +0200 | From | Pavel Machek <> | Subject | Re: [PATCH 3/6] x86_64 UV: Use blinking LED for heartbeat display |
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> > * 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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