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

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

Rather than trying to come up with metrics like this, I'd rather have
vm-top show the percentage of a physical CPU that each domain used,
independent of it's allocation.
i.e. total including the idle domain will be #CPUS x 100%.

Ian

> >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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