Re: cpu hotplug

[Gleb Natapov <gleb@redhat.com>]

On Mon, Sep 20, 2010 at 09:07:16PM -0400, Kevin O'Connor wrote:
> On Mon, Sep 20, 2010 at 08:50:17AM +0200, Gleb Natapov wrote:
> > On Sun, Sep 19, 2010 at 06:03:31PM -0400, Kevin O'Connor wrote:
> > > I was wrong.  The "cpu_set x offline" does send an event to the guest
> > > OS.  SeaBIOS even forwards the event along - as far as I can tell a
> > > Notify(CPxx, 3) event is generated by SeaBIOS.
> > > 
> > > My Windows 7 ultimate beta seems to receive the event okay (it pops up
> > > a dialog box which says you can't unplug cpus).
> > > 
> > It may react to Eject() method.
> 
> The eject method is called by the OS to notify the host.  Right now
> SeaBIOS's eject method doesn't do anything.
> 
> > > Unfortunately, my test linux guest OS (FC13) doesn't seem to do
> > > anything with the unplug Notify event.  I've tried with the original
> > > FC13 and with a fully updated version - no luck.
> > > 
> > > So, I'm guessing this has something to do with the guest OS.
> > > 
> > Can you verify that _STA() return zero after cpu unplug?
> 
> I've verified that.  I've also verified that Linux doesn't call the
> _STA method after Notify(CPxx, 3).  It does call _STA on startup and
> after a Notify(CPxx, 1) event.  So, the Linux kernel in my FC13 guest
> just seems to be ignoring Notify(3) events.  (According to ACPI spec,
> the guest should shutdown the cpu and then call the eject method.)
> 
To remove cpu completely you need to eject it from the guest:
echo 1 > /sys/bus/acpi/drivers/processor/LNXCPU\:03/eject

I didn't found a way to trigger this from a host. May be with some udev
magic it can be done.

--
			Gleb.