[libvirt] [RFC] Add persistent XML for cpu tunables

[Nikunj A. Dadhania]

On Tue, 29 Mar 2011 15:31:19 +0800, Daniel Veillard <veillard at redhat.com> wrote:
> On Tue, Mar 29, 2011 at 02:32:18PM +0800, Osier Yang wrote:
> > Example of cputune XML:
> >   <cputune>
> >     <shares>2048</shares>
> >     <vcpupin vcpu='0' cpuset='0-4,^1'/>
> >     <vcpupin vcpu='1' cpuset='1,3'/>
> >     <vcpupin vcpu='2' cpuset='0,2'/>
> >   </cputune>
> > 
> > "shares" is to define the the proportional weighted cpu share
> > for the domain.
> 
>   Hum, what does "2048" there means ? I assume there is an unit but
> it's not defined. Can we get a precide definition of the semantic of
> the shares construct. If I were to use it I need to know what it means,
> and I can't just from that description. Drivers in QEmu and LXC just
> pass that down to linux, but it still doesn't provide a semantic for
> it and "whatever linux implements at the time" is not really a good
> answer.
> 
The number is relative wrt other domains/cgroup, so if we have two VMs
each having 2048, both of them will get equal share, i.e. 50% each. In a
different scenario, if we have VM1's share as 1024 and VM2's share as
2048, that translates as VM1=33% and VM2=66% share of the CPU.

Regards
Nikunj