[libvirt] How can I improve the performance of libvirt when running many virtual machines on same host

[Diego Dias]

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
>
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