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From Nik Martin <>
Subject Re: CPU (in MHz) in Computer Offering
Date Fri, 11 Jan 2013 17:50:58 GMT

The answer to your question is "Yes".

Specifically, you if you do not place CPU caps on your service offerings, 
you can over subscribe CPUs,  so that if you have 4000 mHz on a server, 
and combination of VMs will share that 4000 mHz, and when the physical 
cpus are all maxed out, xenserver uses a fair scheduling algorithm to 
limit each cpu to their fair share of CPU, but a Virtual CPU with 500 mHz 
without a cap can use all the mHz available to it.  Service Offerings with 
a CPU cap are hard limited to the mHz in the service offering. In this 
case, I'm not 100% sure what Cloudstack/Xenserver does from a 
fair scheduling perspective, but I think you can still oversubscribe the 
physical CPUs.



Nik Martin
+ x1003
Relentless Reliability

On Fri, 11 Jan 2013, Wuming Zhang wrote:

> Hi everyone, I'm wondering if I have understand Computer Offering correct.
> Imagine I have one physical server that is 2Ghz with two cores. So 2 cores
> and total 4000Mhz
> If I want run 10 VM on it, should
> CPU (in MHz): 400Mhz
> # of CPU Cores: 1?
> If I want to run 40 VM on it, should
> CPU (in MHz): 100Mhz
> # of CPU Cores: 1?
> Is my assumption correct? Thanks in advance!
> -- 
> Regards/Vänliga hälsningar/Zhi yi
> Wuming Zhang
> - PGP KEY ID: 0xF4C7755C
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