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

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).


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