Thanks for the answer.

I will try to allocate more memory to Dom0 (it is running wih 2GB on a physical host with 64GB) and see if libvirtd/xend are swapping.

I said the magic number 35 because I was running 54 guests on that host and xend was really slow (around 5 minutes to execute a "xm list" and up to 2h to do a "xm migrate") and libvirtd was not executing at all, and when I got 34 both xend and libvirtd started to work with good performance.

Diego

On 01/19/2011 11:57 PM, Daniel Veillard wrote:

On Wed, Jan 19, 2011 at 04:45:04PM -0200, Diego Dias wrote:

Hi,

   I am using Xen 4 as hypervisor and using libvirt 0.8.4 to
communicate with it.
   When I run more than 35 virtual machines on the host, Libvirt
starts to run extremely slow and I cant even execute a /"virsh
list/". The memory usage of libvirtd is around 468288K.
   Is there any way to improve the performance of libvirt? Is there
any maximum number of virtual machines libvirt can manage without
having a poor performace?

  Well I have run up to 400 guests, but running KVM on a rather large
machine, and the responsiveness of libvirt wasn't a problem (well we had
a trouble with cgroups, but once that one solved that was okay).
In a xen environemnt libvirt doesn't talk directly to the hypervisor
(well except for only a few simple commands where we can use the
hypervisor traps directly) and mostly talks to the xen daemon. Trying to
find out where the slowdown comes from is the only way to improve performances
reliably, and well it's hard to tell from your mail. I would assume 400MB
libvirtd instance is actually realatively small compared to the volume of
memeory used by the guests, just make sure that there is enough memory
in Dom0 and that libvirtd/xend/etc... aren't swapping, that would make the
whole thing slow down considerably.

Daniel