CPU Wait Statistics

[IOWDave]

Good Afternoon,

I would like to ascertain the vCPU wait time for a VM. If I look at the VM.CPU Performance History report then I can add the cpuWaitPct counter to the report. Unfortunately this does not appear to provide me with the information that I am seeking and seems to be simply the inverse of the cpuUsedPct counter.

As I understand it, in order to see the true wait time of a vCPU I would run esxtop, expand the world, and subtract the %IDLE counter from the %WAIT counter for a particular vCPU. This would then give me the amount of time that the vCPU is truly waiting for I/O.

Does anyone know if it is possible to extract that information via the MP as there are times when this would be very useful in order to troubleshoot historical performance problems?

Thanks,
Dave.

[Alec King]

Hello Dave,

The cpuWaitPct counter in our MP is calculated using the cpuWait metric from vCenter. cpuWait is in milliseconds; we convert this to percentage by simply calculating the cpuWait in ms over the performance sample interval in ms.
So cpuWaitPct is definitely not simply an inverse of cpuUsedPct - although if you display both on the same graph you can see what looks like inverse behaviour, this is due to the nature of the metrics (as a VM uses CPU, it is of course not waiting for CPU...)

We do deliver cpuWaitPct as an average across all vCPU cores, as with cpuUsedPct.

And we don't deliver Idle for vCPUs in the current release - however it will be added in our next update, as cpuIdlePct.

I'd also advise adding cpuReady into your troubleshooting, we capture this as cpuReadyPct. In 5.7 release we added cpuSwapWait and cpuLatency, also important metrics.

BTW - apologies for delay in replying, this forum does not always email me for new posts. And moving it to the Cloud hasn't helped

Hope the above helps!
Regards
Alec