Re: x86: kvm: Revert "remove sched notifier for cross-cpu migrations"

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On Mon, Mar 23, 2015 at 4:21 PM, Marcelo Tosatti <mtosatti@xxxxxxxxxx> wrote:
>
> The following point:
>
>     2. per-CPU pvclock time info is updated if the
>        underlying CPU changes.
>
> Is not true anymore since "KVM: x86: update pvclock area conditionally,
> on cpu migration".
>
> Add task migration notification back.

IMO this is a pretty big hammer to use to work around what appears to
be a bug in the host, but I guess that's okay.

It's also unfortunate in another regard: it seems non-obvious to me
how to use this without reading the cpu number twice in the vdso.  On
the other hand, unless we have a global pvti, or at least a global
indication of TSC stability, I don't see how to do that even with the
host bug fixed.

Grumble.

On a more useful note, could you rename migrate_count to
migrate_from_count, since that's what it is?

--Andy
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