[Xen-devel] RE: [PATCH 2/2] Add physical CPU hotplug support in PV_ops dom0

["Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>]

Jeremy Fitzhardinge wrote:
> On 09/24/09 17:27, Jiang, Yunhong wrote:
>> Do you mean logical offlining or physical offlining? I think
> logical offlining is tested long before. For physical
> offlining, I implement it but I have no platform to test still.
>> 
>> In fact , it is  a tricky to physical offlining a cpu (or,
> more precisely speaking, socket) because that means we need
> offline all memory behind a socket. But it can be used for
> socket migration, i.e. put down the old CPU and bring up a
> spare CPU, in that situation, we need CPU offlining. We are
> still working on socket migration.
>> 
> 
> I see.  I guess it makes it hard when the CPUs are also the memory
> controllers. 
> 
>> Yes, also MCE.
>> And, are you sure currently the microcode driver really not
> called in hotplug of vcpus? Will vcpu online not trigger the
> CPU_online notifier?
>> 
> 
> I would expect vcpu hotplug will call the usual notifiers as expected,
> but drivers which really care about pcpus don't have much use for
> those notifications.

Yes.

>>> This could do with some clarification.  Is this case that a newly
>>> added pcpu already appears to be online?
>>> 
>> Because the vIRQ notification for pcpu hotplug from xen
> hypervisor is async, so maybe it happens after the pcpu is
> onlined by user. (i.e., the online notification and hotplug
> notification is merged)
>> 
> 
> I'm not sure I follow.  Are you saying this is an expected race, and
> that this printk is just for debugging?

Yes, exactly.

--jyh
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