[libvirt-users] Quadratic function-like call delay

[Daniel P. Berrange]

On Mon, Sep 24, 2012 at 09:46:08PM +0800, Daniel Veillard wrote:
> On Mon, Sep 24, 2012 at 01:35:21PM +0100, Daniel P. Berrange 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.
> 
>   Hum, IIRC there was a time where libvirtd would not process any
> request until those reconnections were done, did that change ?

Yes, a little while back we introduced code which spawns a background
thread at startup to handle re-connect of VMs, so that libvirtd is not
blocked for a long time.

Regards,
Daniel
-- 
|: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org              -o-             http://virt-manager.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org       -o-       http://live.gnome.org/gtk-vnc :|