AIX 5L Problem Determination - IBM Redbooks

The cs column
The cs column shows the number of context switches per second observed in
the interval. The physical CPU resource is subdivided into logical time slices of
10 milliseconds each. Assuming a thread is scheduled for execution, it will run
until its time slice expires, until it is preempted, or until it voluntarily gives up
control of the CPU. When another thread is given control of the CPU, the context
or working environment of the previous thread must be saved and the context of
the current thread must be loaded. The operating system has a very efficient
context switching procedure, so each switch is inexpensive in terms of
resources. Any significant increase in context switches, such as when cs is a lot
higher than the disk I/O and network packet rate, should be cause for further
investigation.
If the system has low performance because of a lot of threads on the run queue
or threads waiting for I/O, then ps command output will be useful in determining
which process has used the most CPU resources.
10.1.3 The ps command
The ps command is a flexible tool for identifying the programs that are running on
the system and the resources they are using. It displays statistics and status
information about processes on the system, such as process or thread ID, I/O
activity, and CPU and memory utilization.
The ps command output and CPU monitoring
Three of the possible ps command output columns report CPU usage, each in a
different way, as provided in Table 10-1.
Table 10-1 CPU-related ps output
Column Value
C Recent CPU time used for a process.
TIME Total CPU time used by the process since it started.
%CPU Total CPU time used by the process since it started, divided by the
elapsed time since the process started. This is a measure of the CPU
dependence of the program.
The C column
The C column can be generated by the -l flag and the -f flag. In this column, the
CPU utilization of processes or threads is reported. The value is incremented
each time the system clock ticks and the process or thread is found to be
running. Therefore, it also can be said to be a process penalty for recent CPU
usage. The value is decayed by the scheduler by dividing it by two once per
Chapter 10. Performance problem determination 241