Observation

The utilization values (dark green lower area) in the previous figure show the active CPU usage, in units of CPUs based on Linux™ sar data.

That way, the utilization values show which fraction of the available four virtual CPUs was available and actively used for processing the transactional database workload. On the other hand, the steal values (bright green upper area) show how much CPU power was not available in spite of a CPU demand by the virtual system because z/VM® had to perform other activities such as servicing another virtual processor or perform other hypervisor tasks. In other words, the CPU power reflected by the steal value was not available for processing the transactional workload. The remaining free space (grey area on top) reflects CPU capacity not requested from the guest.

It can be seen that after an initialization phase between 2 and 2.5 CPUs are consumed. As the relocation process starts after about seven minutes, during the initial phase of the relocation the utilization values first slowly and then progressively decrease. At the same time, the steal values increase correspondingly.

One additional point must be mentioned here: It is known that for the testcase shown in Figure 1 the quiesce time was 2.2 seconds. During the quiesce time, the virtual processors of the guest system are not dispatched by z/VM, such that during the quiesce time the number of CPUs covered by the steal value would have to show a value of 4 CPUs. However, the sampling rate for the Linux sar values is six seconds. Thus, the resolution for the values shown in Figure 1 is also six seconds. For that reason, the effective stoppage of the virtual processors during the quiesce time is not really visible from Figure 1.

After the relocation is completed, a sharp rise of the utilization values can be observed, followed by a phase of much larger utilization values between 3.3 and 3.7 CPUs. At the same time, the steal values now remain almost insignificant below 0.1 CPUs.