vmware – cpu ready (what to look for) and performance

keeping things simple – below are the numbers to look for when your investigating cpu scheduling issues withing a vmware environment…

Look for the cpu “ready” counter which is a percentage of time that the virtual machine was ready, but could not get scheduled to run on the physical CPU. CPU ready time is dependent on the number of virtual machines on the host and their CPU loads.

These are the peak / average figures to watch for in vmware performance graphs. Anything above 5% cpu ready time is worth fixing. (Note : the sampling rate is different depending on which view you are looking at)

Realtime : 1000 x 20 (20 second sample) x 5% = 1000

Daily : 1000 x 300 (5 min sample) x 5% = 15000
Weekly : 1000 x 1800 (30 min sample) x 5% = 90000
Monthly : 1000 x 7200 (2hrs sample) x 5% = 360000

Note : above is 1vCPU only, see this reference for some more detail and some nice charts!