Re: [Xen-devel] Calculating real cpu usage of Xen domains correctly!

[Anthony Liguori <aliguori@xxxxxxxxxx>]

Jerone Young wrote:

> 1) CPU time % measured per domain
> (The differential of cpu usage time / some differential time) x 100
> new_cpu_time-old_cpu_time           new_time-old_time 
>  
So for instance, measured over the course of a second, you might get:

Domain-0:  98%
Domain-1: 99%
Domain-2: 0%

Which implies that both Domain-0 and Domain-1 are actively running 
Domain-2 is probably blocked on IO.  The typical expectation is that the 
sum of all the usages is going to be 100%.
> 2) Relative usage .. How much of the total of the cpu times is going
> toward a particular domain.
>  
The idea here is to have a relative measure.  So if Domain-0 used 98% of 
it's time, and Domain-1 used 99%, then the result is something like:
Domain-0: 49%
Domain-1: 50%
Domain-2: 0%

That looks more right.  However, we think that means making assumptions 
about the underlying scheduling algorithm (meaning that if the 
difference in cpu_time over a period of time is the same for two 
domains, that those two domains have gotten the same amount of CPU time).
Any advice or recommendations would be greatly appreciated.

Regards,
Anthony Liguori


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