Use the Character-Cell Real-time Display › Evaluate Performance Using the Investigate Displays › Investigate a CPU Limitation

Investigate a CPU Limitation

The chief indicators of a CPU limitation are as follows:

Processes in the CPU queue

Look at the value of CPU queue and at processes in the COM/CUR states in the Priority bars.

CPU que gives the number of processes waiting for the CPU (COM state). There is a real queue if this value is greater than 1. (The process displaced by Performance Manager; the NULL process is not counted.) The existence of a real CPU queue indicates a CPU limitation.

A significant number of processes in the COM/CUR states (COM = computable, waiting for the CPU; CUR = the current process) also indicates a CPU queue, and consequently a CPU limitation.

No idle time

Look at the Idle (Idl) bar in the center of the display. If there is no CPU idle time, then the CPU is a limitation.

System CPU time high

Compare the system CPU time (sum of Int/Ker/Exe bars) with the task CPU time (sum of Sup/Com/Use bars). The system CPU time is the sum of time spent on the interrupt stack, and in kernel and executive modes. The task CPU time is the sum of time spent in supervisor, compatibility, and user modes. The sum of interrupt and kernel CPU time should not exceed 40 percent in most environments.