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ChrisPD
Contributor
Contributor

CPU Contention counter

This might have been asked before but i cant find anything specific.

Can anyone tell me exactly what the CPU Contention counter is actually measuring? I wasnt sure if its ready + co-stop + possibly swap-wait but i cant find an actual definition. Is there any documentation concerning this? Wondering if i sound be using RDY like ive always done, or the CPU Contention, they are different.

Thanks!

Chris

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mark_j
Virtuoso
Virtuoso

No specifics available on the equation used to calculate this. It does involve CPU wait / ready factors. The question you should ask yourself, is, is there any reason to know the exact calculation? If there is no contention, there is no contention.. if there is contention, it'll show it. Are you trying to measure the 'degree' of contention? Contention isn't a granular metric.. it's a derived metric. Once you see there 'is' contention, you can pretty quickly check the specific counters for ready/wait etc to see the specifics. The contention metric is intended to save you time from watching 'multiple' specific counters where you can simply look at one counter, contention, and see a overall stat.

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Jemimus
Contributor
Contributor

We have run into an issue where the ESX Host was putting CPU Cores into power saving C-states. (even though it wasnt suppose to, v1.0 BIOS of Dell Poweredge R630)

This caused CPU contention that was not easily visible. %RDY, %CSTP, %VMWait where all low.  But in vROPS, it was showing a %contention value of anywhere between 5% and 65%


It turns out that this was visible in the $LAT_C  metric, but no where else.


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%LAT_C Percentage of time the resource pool or world was ready to run but was not scheduled to run because of CPU resource contention.

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This metric can be made visible in ESXTOP, by turning on the extra columns option "i" (  SUMMARY STATS = CPU Summary Stats )

Also, the Latency metric van be seen in the vSphere client if you have stastics turned up high enough.

In any case, I know now that %LAT_C is also used for the vROPS %Contention counter.

I suspect that there are also several disk and network i/o metrics that go into it.

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