Re: cpu hotplug

[Gleb Natapov <gleb@redhat.com>]

On Sun, Sep 19, 2010 at 12:04:51PM -0400, Kevin O'Connor wrote:
> On Sun, Sep 19, 2010 at 05:53:47PM +0200, Gleb Natapov wrote:
> > On Sun, Sep 19, 2010 at 05:44:00PM +0200, Conrad Wood wrote:
> > > 
> > > > > However after step 7 the guest can turn the cpu online again by issuing 
> > > > > echo 1 >/sys/devices/.../cpuX/online
> > > > There will be no /sys/devices/.../cpuX/online in guest after step 7.
> > > 
> > > Well then at least in my version there's a bug, because it still is
> > > there and never goes away. (kvm 0.12.5)
> > > And changing it to online works as well.
> > Can you provide exact steps you are using? After doing cpu_set x offline
> > cpu x should disappear from a guest. Otherwise cpu eject didn't work.
> 
> I'm confused.  The "cpu_set x offline" doesn't appear to do anything
> for me.  It does not disable the cpu, nor does it inform the guest to
> disable the cpu.
> 
> The only way I'm able to remove a cpu is to run in the guest:
> 
> echo 1 > /sys/devices/LNXSYSTM:00/LNXSYBUS:00/LNXCPU:xx/eject
> 
> which (as far as I know) is purely a voluntary guest disable of the
> cpu.  It doesn't (as far as I know) even tell kvm that it is no longer
> using the cpu.  (The acpi cpu eject method in seabios just issues a
> sleep(200) call.)
> 
Then cpu eject method in seabios has a bug. When "cpu_set x offline" is
called qemu sets status bit in gpe and injects ACPI interrupt. ACPI
should do Notify() on cpu object when it happens. 

--
			Gleb.