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SubjectRE: [PATCH v4 1/4] powerpc/85xx: add HOTPLUG_CPU support
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> >  struct smp_ops_t smp_85xx_ops = {
> > .kick_cpu = smp_85xx_kick_cpu,
> > -#ifdef CONFIG_KEXEC
> > +#ifdef CONFIG_HOTPLUG_CPU
> > + .cpu_disable = generic_cpu_disable,
> > + .cpu_die = generic_cpu_die,
> > +#endif
> > .give_timebase = smp_generic_give_timebase,
> > .take_timebase = smp_generic_take_timebase,
> > -#endif
> > };
>
> We need to stop using smp_generic_give/take_timebase, not expand its use.
> This stuff breaks under hypervisors where timebase can't be written. It
> wasn't too bad before since we generally didn't enable CONFIG_KEXEC, but
> we're more likely to want CONFIG_HOTPLUG_CPU.

I understand that the guest OS shouldn't change the real timebase. But no matter what timebase syncing method we are using, the timebase need to be changed anyway for certain features. I think the better way should be trapping timebase modification in the hypervisor.

>
> Do the timebase sync the way U-Boot does -- if you find the appropriate
> guts node in the device tree.

That involves stopping timebase for a short time on all cores including the cores that are still online. Won't this be a potential issue?

- Leo



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