On Mon, 1 Oct 2007, Andi Kleen wrote: > > > IRQ_NOBALANCING is not preventing cpu unplug. It moves the affinity to the > > next CPU, but the check in NMI watchdog for CPU == 0 would not longer > > work. > > That cannot happen right now because cpu_disable() on both i386/x86-64 > reject CPU #0. So just setting IRQ_NOBALANCING is sufficient and both > do that already. I was wrong earlier in being concerned about this. > > > int tick_do_broadcast(cpumask_t mask) > > @@ -137,6 +147,7 @@ int tick_do_broadcast(cpumask_t mask) > > cpu_clear(cpu, mask); > > td = &per_cpu(tick_cpu_device, cpu); > > td->evtdev->event_handler(td->evtdev); > > + tick_broadcast_account(cpu); > > That would not handle the case with a single CPU running only > irq 0 but not broadcasting I think. Hmm. The only situation where this can happen is when you add "nolapic_timer" to the command line on a single CPU system. We do not register the lapic "dummy" clock event device then. > I believe > ftp://ftp.firstfloor.org/pub/ak/x86_64/quilt/patches/fix-watchdog > is the correct fix Yup, I completely missed the fact, that we reject CPU#0 unplugging, so your fix seems indeed to be more correct and simpler. OTOH, the accounting hook would allow us to remove the IRQ#0 -> CPU#0 restriction. Not sure whether it's worth the trouble. tglx - To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
