Re: [Xen-users] vCPUs and Weight/Caps

[Peter Viskup <skupko.sk@xxxxxxxxx>]

On 01/13/2013 07:33 PM, Peter Viskup wrote:
> On 01/13/2013 06:12 PM, Mohamed King wrote:
> > Hi Peter,
> >
> > Thanks for the response. I did look at the docs prior to asking. I 
> > guess what I am asking is what the advantages would be if you have 
> > say 2 vCPUs on a VM.
> >
> > Sent from my iPad
> Hi Mohamed,
> I understand its advantage as better possibility to schedule provided 
> CPU time between the processes within the VM. Of course your VM will 
> not be able to use more than 100% of one physical CPU, but should be 
> able to run another process once one will block the first vCPU (and 
> only in case the VM will still have enough credits on hypervisor - if 
> credit scheduler is used). It's good to have more vCPUs on webhosting 
> for example and on all systems where do you expect parallel data 
> processing (webservers, databases, virtual desktop, ...).
> This is my understanding. <correct me if I'm wrong>
>
> Best regards,
> --
> Peter Viskup
Just one other thing where it is expected to have more vCPUs.
You are not allowed to assign more cap than 100% to VM with only one 
vCPU. In other words one vCPU can have a max. of 100% of real CPU power. 
That means in case you need to assign more CPU time to the VM you need 
to setup more vCPUs for that VM - based on the VM requirements (e.g. at 
least 3vCPUs for VM with cap=280).
BR,
--
Peter

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