Re: [Qemu-devel] [PATCH 0/4] s390: Allow hotplug of s390 CPUs

[Christian Borntraeger <borntraeger@de.ibm.com>]

Am 09.11.2015 um 16:37 schrieb Christian Borntraeger:
> Am 09.11.2015 um 16:35 schrieb Christian Borntraeger:
>> Am 09.11.2015 um 16:28 schrieb Andreas Färber:
>>> Hi,
>>>
>>> Am 09.11.2015 um 16:17 schrieb Matthew Rosato:
>>>> To subsequently hotplug a CPU:
>>>>
>>>> Issue 'cpu-add <id>' from qemu monitor, or use virsh setvcpus --count <n> 
>>>> <domain>, where <n> is the total number of desired guest CPUs.
>>>
>>> What exactly is still missing for you to use the standard device_add?
>>>
>>> Last time I checked (a while ago...) some patches were stuck on the x86
>>> side, and I don't recall hearing any feedback from the s390x side in my
>>> KVM Forum CPU hotplug session.
>>
>> libvirt uses "cpu-add" unconditionally for hotplugging, so we certainly 
>> want to support that. 
> 
> Sorry, hit send too early. I assume you want us to support device_add of
> a CPU in addition to that. Correct? 

I just did a quick test with Matts patch.

after applying

diff --git a/qom/cpu.c b/qom/cpu.c
index fb80d13..8152744 100644
--- a/qom/cpu.c
+++ b/qom/cpu.c
@@ -360,7 +360,7 @@ static void cpu_class_init(ObjectClass *klass, void *data)
      * Reason: CPUs still need special care by board code: wiring up
      * IRQs, adding reset handlers, halting non-first CPUs, ...
      */
-    dc->cannot_instantiate_with_device_add_yet = true;
+//    dc->cannot_instantiate_with_device_add_yet = true;
 }
 
 static const TypeInfo cpu_type_info = {

I was able to use

device_add s390-cpu

but no comprehensive testing was done.
I was even able to add more cpus than maxcpus, but the guest could not
make use of it. Fix is probably easy. But in general it looks like
that we _could_ enable device_add for CPUs as soon as others are ready
as well.
Matt, do you agree?



Christian