You can find sample scripts that are distributed with the installation of SystemTap in the /usr/share/systemtap/examples directory.

Use the stap command to run different SystemTap scripts:

Tracing function calls

You can use the para-callgraph.stp SystemTap script to trace function calls and function returns.

# stap para-callgraph.stp <argument1 argument2>

The script takes two command-line arguments:

• The name of the function(s) whose entry/exit you are tracing.
• An optional trigger function, which enables or disables tracing on a per-thread basis.

  Tracing in each thread continues as long as the trigger function has not exited.

Monitoring polling applications

You can use the timeout.stp SystemTap script to identify and monitor which applications are polling. Knowing this, you can track unnecessary or excessive polling. It can help you to pinpoint areas for improvement in terms of CPU usage and power savings.

# stap timeout.stp

This script tracks how many times each application uses poll, select, epoll, itimer, futex, nanosleep, and Signal system calls over time.

Tracking system call volume per process

You can use the syscalls_by_proc.stp SystemTap script to see what processes are performing the highest volume of system calls. It displays the top 20 processes by default.

# stap syscalls_by_proc.stp

Tracing functions called in network socket code

You can use the socket-trace.stp SystemTap script to trace functions called from the kernel’s net/socket.c file. This helps you to identify how each process interacts with the network at the kernel level in fine detail.

# stap socket-trace.stp

Tracking I/O time for each file read or write

Use the iotime.stp SystemTap script to monitor time taken for each process to read from or write to any file. This helps you to determine what files are slow to load on a system.

# stap iotime.stp

Tracking IRQ’s and other processes stealing cycles from a task

Use the cycle_thief.stp SystemTap script to track the time a task is running and the amount of time it is not running. This helps you to identify which processes are stealing cycles from a task.

# stap cycle_thief.stp -x pid

For more information, see the /usr/share/systemtap/examples directory.

Note

You can find more examples and information about SystemTap scripts in the /usr/share/systemtap/examples/index.html file. Open it in a web browser to see a list of all the available scripts and their descriptions.