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

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

> OK, here is a patch which provides fine grained cpu utilization 
> reporting. Some notes:

I really can't see the point of this patch -- it isn't necessary to log
every scheduling operation to record CPU usage for a domain over
multiple time scales. 
Simply exporting the cumulative CPU usage for all domains and polling it
from dom0 will enable you to do this. If you do really want to log such
data, why not use the existing trace buffer infrastructure (though
admittedly it could do with some improvements -- it should be possible
for the user space reader to block until the event buffer becomes
half-full rather than having to poll, but I don't believe anyone has
added this functionality yet -- volunteers?).

Xen is already supposed to be doing the accounting -- though it has been
suggested there is a bug, which needs to be investigated. Its possible
it got broken when SMP guest support was added. If we do per VCPU
accounting the totals can be added to do per-domain. We should also
record the per physical CPU cumulative (non-idle domain) utilization
too.

Calculating utilization averages can be done with a simple user-space
tool. BTW: there are a couple of nice libaries for suporting simple
calculation of multi-scale rolling averages.

Ian

> - part of the code runs in the hypervisor to collect data, 
> and another 
> part of it runs in dom0 userland to process and display the data
> - the code contains vestiges of old features, and partially 
> implemented 
> new features; it is a work in progress.
> - this is the first time I'm sending out a patch to this list 
> so please 
> be gentle on me ;-)
> 
> Feedback appreciated!
> 
> Rob Gardner
> 
> 


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