[libvirt] Ability to nice KVM processes

[Daniel P. Berrange]

On Tue, Sep 09, 2008 at 10:23:59PM +0100, Henri Cook wrote:
> Hey all,
> 
> I'd quite like the ability to nice my KVM process, on a home basis this
> stops my Windows VM locking up my linux desktop when it's under load (or
> at least limits it) and in a commercial setting it might be nice to
> offer CPU priority to other customers or company backup-services over
> customer VPS instances for example.
> 
> How does it sound? Any thoughts?
> 
> A quick chat in #virt revealed that a method for adding generic KVM
> options has been under discussion for ages - I thought i'd throw my two
> cents in, what about some sort of expression with variables like:

A method for adding arbitrary KVM options will never be merged in
libvirt....

> <cmdstring>{cmd} {options}</cmdstring> (default)
> 
> for my nice proposition you could:
> 
> <cmdstring>/usr/bin/nice {cmd} {options}</cmdstring>

The intent of libvirt is to provide APIs which can be used across all
hypervisors. Taking the 'nice' example, this is really a schedular
parameter. If we added ability to set 'nice -20' in the XML for KVM,
there is no way we could possibly implement this for Xen. 

So the goal is to find a consistent API representation. Fortunately we
do already have a 'schedular parameters' API in libvirt - we simply
need to decide how to implement this for KVM - a 'nice' setting is
certainly one schedular tunable we'd likely want to support.

So if someone wants to implenment the schedular parameters driver API
for KVM patches welcomed... 

Regards,
Daniel
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