Re: [RFC 07/10] powermac: support G5 CPU hotplug

Pavel Machek
2007-02-06T12:42:12Z

Hi!

> This patch allows "hotplugging" of CPUs on G5 machines. CPUs that are
> disabled are put into an idle loop with interrupts hard-disabled, to wake
> them up again we kick them just like when bringing them up.
>
> Maybe there's some way to actually turn off those CPUs even more?
>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>

> --- mb-wireless.orig/arch/powerpc/kernel/smp.c 2007-02-05 16:07:09.274524763 +0100
> +++ mb-wireless/arch/powerpc/kernel/smp.c 2007-02-05 18:15:51.114524763 +0100
> @@ -558,6 +558,11 @@ int __devinit start_secondary(void *unus
>
> local_irq_enable();
>
> + /* it seems to be possible that we died from within
> + * an interrupt ... reset the in-irq counts */
> + task_thread_info(paca[cpu].__current)->preempt_count &=
> + ~(SOFTIRQ_MASK|HARDIRQ_MASK);
> +
> cpu_idle();
> return 0;

This is quite a nasty hack. Are you sure?

I've seen similar weirdness on pc, and it was caused by
swsusp-copying-code using FPU and incrementing preempt_count...

Pavel
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