Varying physical CPUs on z/VM

Edit online

Because z/VM® has a capacity of more than one CPU free in each case, we did additional CPU scaling tests with z/VM with one physical CPU less, but all virtual CPUs unchanged, which led to an increase of the CPU over commitment.

Table 1 shows the test cases used to produce Figure 1.

Table 1. Varying physical CPUs on z/VM test cases
# of Virtual CPUs - webApp.secure	# of Physical CPUs - z/VM
2	3
2	4
4	4
4	5

Throughput

Figure 1 compares the throughput of the original results with the result having z/VM with one less physical CPU.

ewapp22 — Figure 1. CPU scaling - throughput (HTTP)

Observations: Reducing the number of CPUs for z/VM by one reduces the throughput between 5% and 10%.

Conclusion: The reduction of throughput is expected to be caused by queuing effects. This means that three parallel units for the same work have higher latencies compared with four units. However, saving one CPU might be an advantage, which is worth a slight reduction in throughput. Be aware that we implemented a secure server environment, including a DMZ, which uses seven virtual CPUs on four physical CPUs without any physical network cable.