ftrace

ftrace (abbreviated from Function Tracer) is a tracing framework for the Linux kernel. Although its original name, Function Tracer, came from ftrace's ability to record information related to various function calls performed while the kernel is running, ftrace's tracing capabilities cover a much broader range of kernel's internal operations.^[1][2]

With its various tracer plugins, ftrace can be targeted at different static tracepoints, such as scheduling events, interrupts, memory-mapped I/O, CPU power state transitions, and operations related to file systems and virtualization. Also, dynamic tracking of kernel function calls is available, optionally restrictable to a subset of functions by using globs, and with the possibility to generate call graphs and provide stack usage. At the same time, ftrace can be used to measure various latencies within the Linux kernel, such as for how long interrupts or preemption are disabled.^{[1][3][4]:3–11,14,18}

An ftrace-enabled Linux kernel is built by enabling the CONFIG_FUNCTION_TRACER kernel configuration option. The entire interaction with ftrace is performed through readable and writable virtual files contained in a specifically mounted debugfs file system; as a result, ftrace requires no specialized userspace utilities to operate.^[1][2][5] However, additional userspace utilities exist to provide improved data recording, analysis and visualization features; examples of such utilities are trace-cmd and KernelShark.^{[1][4]:31–47[6]}

ftrace is primarily developed by Steven Rostedt, and it was merged into the Linux kernel mainline in kernel version 2.6.27, which was released on October 9, 2008.^[7]

See also

• DTrace – a tracing framework for troubleshooting kernel and application problems, originally developed for Solaris
• ktrace – a BSD Unix and Mac OS X utility that traces kernel–program interactions
• ltrace – a Linux debugging utility, displays the calls a userland application makes to shared libraries
• strace – a debugging utility for Linux and some other Unix-like systems, monitors system calls used by a program and all received signals
• SystemTap – a scripting language and utility used for instrumenting Linux installations

References

1. Jake Edge (March 13, 2009). "A look at ftrace". LWN.net. Retrieved July 23, 2014.
2. Steven Rostedt (June 16, 2014). "Linux kernel documentation: Documentation/trace/ftrace.txt". kernel.org. Retrieved July 23, 2014.
3. "Red Hat Enterprise MRG 2 documentation, Section 3.8. Using the ftrace utility for tracing latencies". Red Hat. May 23, 2014. Retrieved July 24, 2014.
4. Steven Rostedt (October 18, 2010). "Ftrace: Linux Kernel Tracing" (PDF). linuxfoundation.org. Retrieved July 23, 2014.
5. "Red Hat Enterprise Linux 6 documentation, Section 6.5. ftrace". Red Hat. March 14, 2014. Retrieved July 23, 2014.
6. Steven Rostedt (October 20, 2010). "trace-cmd: A front-end for Ftrace". LWN.net. Retrieved January 19, 2015.
7. "Linux kernel 2.6.27, Section 1.7. ftrace, sysprof support". kernelnewbies.org. October 9, 2008. Retrieved July 23, 2014.

External links

• Debugging the kernel using Ftrace – part 1 and part 2, LWN.net, December 2009, by Steven Rostedt
• Secrets of the Ftrace function tracer, LWN.net, January 20, 2010, by Steven Rostedt
• Ftrace: The hidden light switch, LWN.net, August 13, 2014, by Brendan Gregg
• Using KernelShark to analyze the real-time scheduler, LWN.net, February 2, 2011, by Steven Rostedt
• The source of the e1000e corruption bug, LWN.net, October 21, 2008, by Jonathan Corbet