Re: [Xen-devel] [PATCH] qemu-xen: fix cpu hotplug

[Christoph Egger <Christoph.Egger@xxxxxxx>]

On Friday 03 September 2010 08:28:53 Liu, Jinsong wrote:
> Ian Jackson wrote:
> > Stefano Stabellini writes ("[Xen-devel] [PATCH] qemu-xen: fix cpu
> >
> > hotplug"):
> >> qemu-xen: fix cpu hotplug
> >>
> >> The current xenstore watch path for a vcpu-set event is wrong and is
> >> also wrong the code to parse it.  This patch fixes both of them:
> >
> > Thanks.  So it seems you're saying it's completely broken in
> > xen-unstable.
>
> Stabellini, I read your attached patch, it's OK.
> In fact, we firstly implemented xenstore watch by same scheme of your
> patch, watching each cpu node status:
> /local/domain/xx/cpu/yy/availability=offline (online)
>
> However, we finally didn't use this scheme. We watch 'common' node instead:
> /local/domain/xx/cpu
> in this way, only 1 watch point need.
> Considering vcpu number may become more and more in the future (say, more
> than 128), it's more simple and reasonable. (Watches can be set at points
> in the hierarchy and an individual watch will be triggered when anything at
> or below that point in the hierachy changes)

Does this scheme allow to say how many cores per cpu exist ?

When you run a Windows guest with a license for one cpu socket,
then you can use 4 cores. But if one cpu is equal to one socket,
then you can't use SMP for the Windows guest.

Christoph


>
> > I have CC'd a bunch of Intel folks who were doing some other
> > work on cpu hotplug.  They were dealing with a race when multiple CPUs
> > were added at once.
> >
> > So I think there must be some confusion.  Perhaps xl and xend have
> > different ideas about what the xenstore syntax is for these
> > operations ?
> >
> > Jinsong Liu et al: would you care to comment ?  Particularly about
> >
> > this:
> >> A xenstore vcpu hotplug command is of the following form:
> >> path: /local/domain/DOMID/cpu/VCPU_NUMBER/availability
> >> values: "online" or "offline"
>
> Yes, I think there must be some confusion.
> Currently 'xm vcpu-set' command works fine with both PV and HVM vcpu
> hotplug.
>
> Stabellini/Jackson, would your please tell me what xl recently happened for
> vcpu hotplug? is there any different ideas xl and xend about xenstore
> syntax?
> (Each time 'xm vcpu-set' executed, xend will write all xenstore cpu node
> status)
>
> > That doesn't seem to match up with what's in xend, which seems to
> > write "cpu_avail" in the vm tree.
> >
> > Thanks,
> > Ian.



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