Linux guest performance during the relocation process
Linux performance was monitored by means of the system activity data collector (sadc).
In most cases, a ten second sampling interval was used. However, in order to show the effects of the guest relocation process, for this particular test case a two second sampling interval was used. In order to make the effects of the guest relocation process most apparent, for this test case an ISFC logical link configuration was chosen that causes longer relocation and quiesce times.
Figure 1 shows the steal time percentage observed during the relocation process.
Observation
In Figure 1, a logarithmic scale was chosen for the ordinate in order to highlight the observed effects. Figure 1 shows the steal time percentage over the elapsed time for the relocation process. Initially, the steal time percentage stays at very low values (below 1%). It then rises to and stays at slightly higher values for some time (about 2 to 2.5%), and eventually rises sharply to and stays at a value of 100% for some time. Finally, the steal time percentage falls back to the initial very low value.
Conclusion
The initial constant phase reflects the situation before the live guest relocation is started. Because the Linux guest is the only workload of the source z/VM system, and because the z/VM installation has plenty resources available in terms of processing power and memory, at that time the Linux guest virtual machine receives all required resources, and is able to execute the test workload without constraints imposed by the virtualization platform.
As the live guest relocation process starts, a slightly increased steal time percentage is observed. This is because in that phase z/VM requires some resources to perform the initial memory passes of the live guest relocation.
Then, during the quiesce time, the Linux guest is no longer dispatched by z/VM, and the effective steal percentage is 100%.
After the relocation process finishes, the Linux guest now is running as the only workload of the target z/VM system, and the steal time percentage drops back to its initial very low value.