RE: [Xen-devel] HVM vcpu hotplug (was: shutdown/reboot/sysrq/vcpu-set from dom0 to HVM guest)

["Liu, Jinsong" <jinsong.liu@xxxxxxxxx>]

Stefano Stabellini wrote:
> On Wed, 1 Sep 2010, Stefano Stabellini wrote:
>>> 
>>> For the cpu-set I've modified the file
>>> linux-2.6.36-rc3/drivers/xen/cpu_hotplug.c and the check fo
>>> pv_domain in setup_vcpu_hotlug_event(void).  And then I can remove
>>> CPUs but not add some  :   
>>> 
>>>     xl vcpu-set DOMID 2 -> "CPU 2 is now offline / CPU 3 is now
>>> offline" 
>>> 
>>> I've tried the same modification on ballooning driver and hvc
>>> console one but it gave me a kernel panic ... 
>>> 
>> 
>> In my tree both the ballooning driver and the hvc console should
>> work correctly on hvm. Regarding the pv cpu hotplug mechanism, I
>> don't think is a good idea to enable it on hvm: there must be an
>> alternative fully virtualized way to hotplug a cpu into a non-pv
>> guest, like Windows, and that should work for pv on hvm guests too.
> 
> I have done some testing on cpu hotplug for hvm guests and it turns
> out that it is currently broken on xen-unstable.

Some strange.
Stabellini, would you please tell me more clear?
How did you do the test? what command? and error log?

Thanks,
Jinsong

> I have just sent two patches to fix it.
> Once they got applied you should be able to specify the maximum number
> of vcpus using the "maxvcpus" parameter in your config file; then use
> vcpu-set to dynamically change the number of vcpus in the guest.
> Linux needs to be compiled with CONFIG_ACPI_HOTPLUG_CPU=y in order for
> this to work.
> Once you hotplug a new cpu in the guest you also need to enable it
> manually, with the following command:
> 
> echo -n 1 > /sys/devices/system/cpu/cpu$CPUNUMBER/online
> 
> 
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