AIX 5L Problem Determination - IBM Redbooks

10.1 CPU-bound system
CPU performance problems can be handled in different ways. For example:
► Reschedule tasks to a less active time of the day or week.
► Change the priority of processes.
► Manipulate the scheduler to prioritize foreground processes.
► Implement Workload Manager.
► Buy more CPU power.
Whatever the solution finally will be, the way to the solution is usually the same:
Identify the process (or groups of processes) that constrains the CPU. When
working with CPU performance tuning problems, historical performance
information for comparison reasons is useful, if such is available. A very useful
tool for this task is the sar command.
10.1.1 The sar command
The sar command gathers statistical data about the system. Though it can be
used to gather useful data regarding system performance, the sar command can
increase the system load, which will worsen a pre-existing performance problem.
The system maintains a series of system activity counters. which record various
activities, such as fork rates. The sar command does not cause these counters
to be updated or used; this is done automatically, regardless of whether the sar
command runs. It merely extracts the data in the counters and saves it, based on
the sampling rate specified to the sar command. There are three situations in
which to use the sar command; they are discussed in the following sections.
Real-time sampling and display
To collect and display system statistic reports immediately, use the following
command:
# sar -u 2 5
AIX texmex 3 4 000691854C00 01/27/00
17:58:15 %usr %sys %wio %idle
17:58:17 43 9 1 46
17:58:19 35 17 3 45
17:58:21 36 22 20 23
17:58:23 21 17 0 63
17:58:25 85 12 3 0
Average 44 15 5 35
This example is from a single user workstation and shows the CPU utilization.
Chapter 10. Performance problem determination 235