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Re: [virt-tools-list] Obtaining usable output from virDomainMemoryStats()



On 05/14/2013 08:39 AM, Tadej Janež wrote:
> Eric,
> 
> thanks for taking the time and explaining this in detail.
> 
> On Mon, 2013-05-13 at 11:09 -0600, Eric Blake wrote: 
>>
>> There is work underway to switch to an event-based solution - where qemu
>> periodically asks the guest but without blocking, the guest informs qemu
>> when it wants, and where libvirt can then query the most recent guest
>> information (if any) without blocking, which works to remove the hole of
>> a non-cooperative guest stopping progress.  But until libvirt been has
>> wired up to use the new QMP querying commands for those properties (and
>> for that matter, until you are using a qemu new enough), there's no way
>> for libvirt to report a stat that qemu doesn't provide.
> 
> This seems like a reasonable approach.
> 
> Virt-manager will then have cater for both cases, when libvirt can
> provide this info via QMP query commands and when it can't.

virt-manager doesn't care about the difference.  The libvirt API will
either have information to provide (super-old qemu that blocked on HMP,
or modern API that uses new QMP) or it won't (intermediate qemu that
ditched the info to avoid blocking).  All you have to do is upgrade qemu
and libvirt, and virt-manager will magically start providing stats again.

> 
>> https://lists.gnu.org/archive/html/qemu-devel/2013-01/msg04832.html
>>
>> I couldn't (quickly) find an open bugzilla against libvirt requesting
>> that it start using the qom-get command on new-enough qemu, in order to
>> get guest memory stat reporting back operational.
> 
> I've also searched RH bugzilla tickets for libvirt (product:
> Virtualization Tools), but couldn't find a bug report about this.
> 
> Should I file a new bug report so we can track this?

Yes, please - having it filed by you (as opposed to me) will give it
some more weight when Red Hat evaluates which bugs to fix for RHEL.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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