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EdZ
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ESX performance - ready time calculations

I've been trying to figure out how to measure CPU ready times and how to calcuate ready time percentages. There seem to be some conflicts in what has been posted - I'm hoping to straighten this out once and for all. So there are two sources of CPU ready time values - from ESXTOP there is %RDY and from the VI Client or vCenter there is CPU Ready in milliseconds. Now I have a few questions:

Is the %RDY value in ESXTOP calculated as (CPU Ready Time)/(CPU Used Time) or CPU Ready/Total time per interval, or is it something else?

There seems to be confusion on how to calculate %CPU Ready time from the VI Client/vCenter. Some postings indicate that you should compare CPU Ready Time to CPU Used time, others say to calculate %CPU Ready Time as (CPU Ready Time)/(Total time per sampling interval). For example if a one week interval is being analyzed, the sampling intervals are 30 minutes = 60*30 = 1800 seconds so if Ready Time for one sample was 30 seconds then that would lead to %Ready Time as 30/1800= 1.66%. But doesn't this only matter if Ready Time is a large percentage of CPU Used time?

When viewing CPU time in the VI Client or VCenter, I believe the following statistics should add up to the time per sample interval, so

Sampling interval = CPU Ready + CPU Used + CPU Wait + CPU System

So for realtime, the interval = 20 seconds

20 seconds = 20,000 ms = CPU Ready + CPU Used + CPU Wait + CPU System

For one of my VM's the averages in one interval are:

CPU Used = 362.35

CPU Ready = 12.117

CPU Wait = 19367

CPU System = 1.839

Adding these up gives 19743.306 which is pretty close to 20,000 - the sampling interval.

So given this - which formula should we use?

%CPU Ready = CPU Ready / Sampling interval

or

%CPU Ready = CPU Ready / CPU Used

Thanks,

Ed

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david_drew
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According to the (old VI 3) Performance Counters tech note:

%ready = (readyTime * 100) /statsIntervalPeriodInMilliSeconds

http://www.vmware.com/resources/techresources/1067

So that's the one I'd go with.