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

[Mohamed King <mohammed.king@xxxxxxxxx>]

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

On Jan 9, 2013, at 9:00 PM, Peter Viskup <skupko.sk@xxxxxxxxx> wrote:

> On 01/09/2013 07:30 PM, mohammed.king@xxxxxxxxx wrote:
>> Hello Everyone,
>> 
>> I am hoping I can get some help with how vCPUs work with weights and caps
>> 
>> 1. If I have a domU with 2 vCPUs and a weight of 256, does the weight double 
>> (512) or is this 256 time slice across both vCPUs. If the weight does not 
>> double, how is it beneficial to have multiple vCPUs?
>> 
>> 2. If the domU has 2vCPUs and a cap  of 100% how does this work since 100% 
>> is a mex of one physical CPU.
>> 
>> Thanks,
>> Mohamed
>> _______________________________________________
>> Xen-users mailing list
>> Xen-users@xxxxxxxxxxxxx
>> http://lists.xen.org/xen-users
> 
> Hi Mohammed,
> both of these are related to Credit scheduler [1].
> Weight is domain attribute (not vCPU) and the benefit of this is to 
> effectively distribute the CPU time between the domains. The domain with 
> higher weight has better chance to get CPU time.
> The cap is the maximum of CPU the domain can have available.
> Read the "Algorithm" section on that wiki and everything will be clear for 
> you. It's always better to read some documentation before asking such 
> questions. ;-)
> 
> [1] http://wiki.xen.org/wiki/Credit_Scheduler
> 
> BR,
> --
> Peter Viskup

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