[libvirt-users] Quadratic function-like call delay

[Andrey Korolyov]

On Mon, Sep 24, 2012 at 4:35 PM, Daniel P. Berrange <berrange at redhat.com> wrote:
> On Mon, Sep 24, 2012 at 11:48:44AM +0400, Andrey Korolyov wrote:
>> Hi,
>>
>> There is a quite annoying thing, don`t sure if I can call it a bug.
>>
>> How to reproduce:
>>
>> - start a bunch of VMs,
>> - stop libvirt,
>> - start libvirt and immediately issue any call, say, 'virsh version',
>> - delay until call completion may be fitted nearly as quadratic
>> function from number of running VMs, qemu-kvm in my case (see link
>> below). After this delay passed, any calls executed without slowdown,
>> so problem is only a 'dead gap' after restarting service.
>
> When you restart the libvirtd service, while KVM guests are running,
> the first thing libvirtd needs todo is to connect to the QEMU monitor
> for each guest and figure out its status. This can take some time
> depending on how loaded the host is in general. It will definitely
> slow libvirt API calls which need to query individual VMs, but I'm
> rather surprised that you saw any slowdown of the 'virsh version'
> command, since that should not touch VMs at all. So I think I *would*
> class this as a bug. It could be something silly like the main I/O
> event loop having some badly written bit of non-scalable code. Please
> do file a bug about this, providing as much raw data as you have
> managed to collect.
>

Here is a report, please take a look.

https://bugzilla.redhat.com/show_bug.cgi?id=860053

>
> Daniel
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