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

Ian Pratt wrote:
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.

Yes, obviously you are correct. I am sorry for not explaining this patch better. Let me start from the beginning. We developed this code to collect various kinds of data. One of the things it does is measure cpu usage. However, that is not all it does, since as you rightly say, such complicated code is not necessary to to just measure cpu usage. When several people started talking about measuring cpu usage, I just volunteered this code to solve the problem. So I do not propose this code solely to measure cpu usage.

For instance, one thing the code can do is to measure how much time elapses while a domain is runnable, versus how much cpu time it actually receives. This metric might be one simple way of expressing 'quality of service.' In order to do this, some scheduler activity needs to be monitored. Hence the more heavy handed approach. We have other ideas in mind that require very fine grained measurements, some have been implemented, some not. I hope to share some of the other metrics soon.

Additionally, this is somewhat experimental code in that it was written this way in order to facilitate future measurements that we may not have considered yet. Can we let some people try it out and see if it provides this framework?


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