[libvirt] [RFC] Support cpu hotplug in libvirt.

[tangchen]

Hi～

On 07/18/2012 09:44 AM, Eric Blake wrote:
> On 07/17/2012 07:33 PM, tangchen wrote:
>> Hi~
>>
>> It seems that libvirt is not cpu hotplug aware.
> 
> Portions of libvirt are aware of host hotplug issues, but you are
> correct that there are still lingering bugs (I just found one today in
> nodeinfo.c).

Could you give me some more info about hotplug support in libvirt ?
I tried to find out, but I didn't see any.

> I think this is related to (if not the same as) this known kernel bug:
> https://bugzilla.redhat.com/show_bug.cgi?id=714271
> 
> Basically, when the kernel suspends and then resumes, it is not properly
> restoring descendant cgroup information.  Hot unplug of a host cpu is
> more or less a subset of suspending.
> 
Yes, hot unplug cpu function in kernel is not usable now.
But cgroup doesn't know what value a file used to be. As a result, 
it cannot recover any value in subdirectories.

>>
>>
>> I am trying to use netlink socket with NETLINK_KOBJECT_UEVENT protocol to
>> listen to cpu hotplug events. But I met a little problem here.
> 
> Interesting approach.  Is it also possible to use inotify?

I have tried inotify. But since /sys is a special file system, it seems that 
inotify failed to keep an eye on file systems like /proc, /cgroup or /sys. 

But netlink works fine.

> 
>>
>> virNetlinkEventServiceStart() only create a global variable server, and 
>> create a NETLINK_ROUTE netlink socket for it. 
>>
>> So if I want to create another different netlink socket, such as NETLINK_KOBJECT_UEVENT, 
>> what should I do ?
> 
> I'm not sure here, having not really coded much with netlink sockets
> myself.  If you have a patch pending, then post it and we can discuss
> whether it can be improved.

OK.:)
I'll try, but I am still wondering if anybody else could give me some advice.

Thank. :)

> 
>>
>> Shall we make the server global variable a global array ?
>> (It seems there are a lot of work to do.)
>>
>> Thanks. :)
>>
> 

-- 
Best Regards,
Tang chen