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    SubjectRE: [PATCH v4 1/4] powerpc/85xx: add HOTPLUG_CPU support
    Date
    > >  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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