CPU Configuration Guidelines for vPars

5 Flexing Dynamic CPU Migration on A.04.01

In section 4.2, the CPU configuration for the vPar vpolyc01 was created as a way to simulate the

behavior of bound and unbound CPU’s of vPars versions prior to A.04.01. The path based CPU

assignments represent the bound CPU’s and the count based CPU assignments represent the unbound

CPU’s. Configuring CPU’s by this method allows I/O interrupt processing to execute on a fixed set of

CPU’s. This configuration should exhibit consistent performance since it was derived experimentally to

meet service level objectives of steady state and peak workload conditions. In this section, the CPU

configuration will be taken a step further by allowing the minimum CPU assignment to be set for an

idled or low utilization condition rather than a steady state condition.

The goal of this exercise is to wring out as much CPU utilization as possible by allowing all but the

boot CPU to move from vPars with under-utilized CPU’s to vPars with over-utilized CPU’s. The net

effect is that all I/O interrupts might be assigned to the boot processor and all subsequent CPU

additions to this vPar will not participate in I/O interrupt processing without manual redistribution.

Figure 21 shows the GlancePlus CPU utilization report for a system with disk and networking traffic

applied to it. Notice that an average of 8.4% of total CPU time is spent executing interrupt handling

functions. In reality, all I/O interrupts are assigned to the boot processor. Switching to the GlancePlus

individual CPU report (Figure22) you will notice that CPU 0 is 60% utilized while the other CPU’s are

8.6% to 23.8% utilized. The execution of I/O interrupt handlers is the major contributor to the

disparity in CPU utilization. Processes that are assigned to execute on this CPU may experience long

wait times or may have erratic response times as they are trapped on a CPU that is handling all of the

I/O interrupts.

Figure 21. GlancePlus CPU utilization report with CPU 0 assigned all I/O interrupts.