Re: [libvirt] [RFC] Add persistent XML for cpu tunables
On Tue, 29 Mar 2011 15:31:19 +0800, Daniel Veillard <veillard(a)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