Chapter 6. Monitoring and Tuning CPU Use

The processing unit in a RS/6000 is one of the fastest components of the system. It is comparatively rare for a single program to keep the CPU 100% busy for more than a few seconds at a time. Even in heavily loaded multiuser systems, there are occasional 10ms periods that end with everything in a wait state. If a monitor shows the CPU 100% busy (that is, 0% idle and 0% wait) for an extended period, there is a good chance that some program is in an infinite loop. Even if the program is "merely" expensive, rather than broken, it needs to be identified and dealt with.

This chapter deals with techniques for detecting runaway or CPU-intensive programs and minimizing their adverse effect on performance.

Readers who are not familiar with AIX CPU scheduling may want to look at "Performance Overview of the AIX CPU Scheduler" before continuing.

The following sections cover the different aspects of CPU tuning:

• "Using vmstat to Monitor CPU Use"
• "Using the time Command to Measure CPU Use"
• "Using ps to Identify CPU-Intensive Programs"
• "Using tprof to Analyze Programs for CPU Use"
• "Detailed Control Flow Analysis with stem"
• "Restructuring Executables with fdpr"
• "Controlling Contention for the CPU"
• "Modifying the Scheduler Time Slice"
• "CPU-Efficient UserID Administration"

The xmperf tool is also valuable in monitoring CPU use.