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

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.

Anthony Liguori

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