Re: cpu hotplug

[Gleb Natapov <gleb@redhat.com>]

On Sun, Sep 19, 2010 at 05:16:24PM +0200, Conrad Wood wrote:
> [..]
> 
> > Lets establish some terminology to understand each other better:
> > Lets use CPU inserted/ejected to refer to cpu being available/not
> > available to a guest.
> > Lest use CPU online/offline to refer to cpu been used by a guest OS.
> > 
> > CPU hot-plug works like this:
> >   cpu is inserted (plugged into cpu socket on MB)
> >   guest OS is notifies through ACPI
> >   guest OS starts to use newly added CPU (makes it online)
> > 
> > CPU hot-unplug works like this: 
> >   guest OS is notifies through ACPI that cpu is going to be removed
> >   guest OS stops to use cpu (makes it offline)
> >   cpu is ejected (removed from a socket on MB) (kvm never does that part)
> > 
> > So which part do you want to know about from a host?
> > 
> > You can't really know from a host if cpu is used by guest OS (if it is
> > online/offline in s guest in our terminology)
> > 
> > inserted/ejected is management action (it can't be initiated by a
> > guest), so you can keep track of it by yourself. KVM doesn't do it
> > for you right now. More precisely it does, but doesn't have a way to
> > quire it.
> 
> I need to know if a cpu is currently inserted or ejected.
> 
The only way to do that currently is to track it in your management app.

> I gather a cpu which is currently "inserted", may potentially be used by
> a guest os. (Wether he actually uses a cpu, puts it online or offline,
> isn't my concern). 
> 
> The amount of time and number of cpus available to a guest is what I
> like to keep track of.
> 
> Conrad
> 

--
			Gleb.