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ftrace
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<h2 id="details">Details</h2> <p>With its various tracer plugins, ftrace can be targeted at different static tracepoints, such as <a href="/facts/Scheduling_(computing)/XptmcM1a">scheduling</a> events, <a href="/facts/Interrupt/Mm6C4rpc">interrupts</a>, <a href="/facts/Memory-mapped_I%2fO/PmLNFq01">memory-mapped I/O</a>, <a href="/facts/CPU_power_state/GnLLzfyr">CPU power state</a> transitions, and operations related to <a href="/facts/File_system/FdPm90uc">file systems</a> and <a href="/facts/Virtualization/bEqH0Wtf">virtualization</a>. Also, dynamic tracking of kernel function calls is available, optionally restrictable to a subset of <a href="/facts/Function_(programming)/9vFJrg0A">functions</a> by using <a href="/facts/Glob_(programming)/IIPcqW8o">globs</a>, and with the possibility to generate <a href="/facts/Call_graph/Uk0b0mdN">call graphs</a> and provide <a href="/facts/Call_stack/1sMt713v">stack</a> usage reports. At the same time, ftrace can be used to measure various <a href="/facts/Latency_(engineering)/6Bjhn30H">latencies</a> within the Linux kernel, such as for how long interrupts or <a href="/facts/Linux_kernel_preemption/dlkduHuA">preemption</a> are disabled.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a><a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a><a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a>: 3–11, 14, 18 </p><p>An ftrace-enabled Linux kernel is built by enabling the CONFIG_FUNCTION_TRACER <a href="/facts/Linux_kernel_configuration/jgXEAQvk">kernel configuration</a> option. The entire runtime interaction with ftrace is performed through readable and writable <a href="/facts/Virtual_file/FdPm90uc">virtual files</a> contained in a specifically mounted <a href="/facts/Debugfs/US7VPwTb">debugfs</a> file system; as a result, ftrace requires no specialized <a href="/facts/Userspace/0yIzMY8t">userspace</a> utilities to operate.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a><a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a><a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> However, there are additional userspace utilities that provide more advanced features for data recording, analysis and visualization; examples of such utilities are <i>trace-cmd</i> and <i>KernelShark</i>.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a><a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a>: 31–47 <a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a><a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> </p><p>Internally, ftrace relies on the <a href="/facts/GNU_Compiler_Collection/t07jh01k">gcc</a>'s <a href="/facts/Profiling_(computer_programming)/JbSlDHPP">profiling</a> mechanism to prepend <a href="/facts/Machine_instruction/bgdQ1Fxf">machine instructions</a> to the <a href="/facts/Compile/WNfCDFJe">compiled</a> versions of all <a href="/facts/Source_code/o9J6Jv23">source</a>-level kernel functions, which redirect the execution of functions to the ftrace's <a href="/facts/Trampoline_(computing)/yRLBSWyH">trampolines</a> and tracer plugins that perform the actual tracing. These "<a href="/facts/Entry_point/nN52vHKb">entry point</a>" instructions created by gcc are altered by ftrace when the kernel is <a href="/facts/Booting/j6N1kRpc">booted</a>, and varied later at runtime by ftrace between <a href="/facts/NOP_(code)/uGcGefyG">NOPs</a> and actual <a href="/facts/Unconditional_branch/obBGrnor">jumps</a> to the tracing trampolines, depending on the tracing types and options configured at runtime.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a><a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> </p><p>ftrace is developed primarily by Steven Rostedt, and it was merged into the <a href="/facts/Linux_kernel_mainline/dlkduHuA">Linux kernel mainline</a> in kernel version 2.6.27, which was released on October 9, 2008.<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> </p> <h2 id="see-also">See also</h2> <ul> <li>Computer programming portal</li><li>Linux portal</li></ul> <ul><li><a href="/facts/DTrace/Q5djxLKt">DTrace</a> – a tracing framework for troubleshooting kernel and application problems, originally developed for Solaris</li> <li><a href="/facts/Ktrace/P92pPv1v">ktrace</a> – a BSD Unix and Mac OS X utility that traces kernel–program interactions</li> <li><a href="/facts/Ltrace/TQJec8TL">ltrace</a> – a Linux debugging utility, displays the calls a userland application makes to shared libraries</li> <li><a href="/facts/Strace/hvwty1kU">strace</a> – a debugging utility for Linux and some other Unix-like systems, monitors system calls used by a program and all received signals</li> <li><a href="/facts/SystemTap/vQFvbVdA">SystemTap</a> – a scripting language and utility used for instrumenting Linux systems</li></ul> <h2 id="external-links">External links</h2> <ul><li><a href="https://lwn.net/Articles/365835/">Debugging the kernel using Ftrace – part 1</a> and <a href="https://lwn.net/Articles/366796/">part 2</a>, <a href="/facts/LWN.net/8uTsltvM">LWN.net</a>, December 2009, by Steven Rostedt</li> <li><a href="https://lwn.net/Articles/370423/">Secrets of the Ftrace function tracer</a>, LWN.net, January 20, 2010, by Steven Rostedt</li> <li><a href="https://lwn.net/Articles/608497/">Ftrace: The hidden light switch</a>, LWN.net, August 13, 2014, by Brendan Gregg</li> <li><a href="https://lwn.net/Articles/304105/">The source of the e1000e corruption bug</a>, LWN.net, October 21, 2008, by Jonathan Corbet</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Jake Edge (March 13, 2009). "A look at ftrace". LWN.net. Retrieved July 23, 2014. <a href="https://lwn.net/Articles/322666/" target="_blank">https://lwn.net/Articles/322666/</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Steven Rostedt (June 16, 2014). "Linux kernel documentation: Documentation/trace/ftrace.txt". kernel.org. Retrieved July 23, 2014. <a href="https://www.kernel.org/doc/Documentation/trace/ftrace.txt" target="_blank">https://www.kernel.org/doc/Documentation/trace/ftrace.txt</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Jake Edge (March 13, 2009). "A look at ftrace". LWN.net. Retrieved July 23, 2014. <a href="https://lwn.net/Articles/322666/" target="_blank">https://lwn.net/Articles/322666/</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>"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. <a href="https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_MRG/2/html/Realtime_Tuning_Guide/sect-Realtime_Tuning_Guide-Realtime_Specific_Tuning-Using_the_ftrace_Utility_for_Tracing_Latencies.html" target="_blank">https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_MRG/2/html/Realtime_Tuning_Guide/sect-Realtime_Tuning_Guide-Realtime_Specific_Tuning-Using_the_ftrace_Utility_for_Tracing_Latencies.html</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Steven Rostedt (October 18, 2010). "Ftrace: Linux Kernel Tracing" (PDF). linuxfoundation.org. Archived from the original (PDF) on March 8, 2013. Retrieved July 23, 2014. <a href="https://web.archive.org/web/20130308164230/http://events.linuxfoundation.org/slides/2010/linuxcon_japan/linuxcon_jp2010_rostedt.pdf" target="_blank">https://web.archive.org/web/20130308164230/http://events.linuxfoundation.org/slides/2010/linuxcon_japan/linuxcon_jp2010_rostedt.pdf</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Jake Edge (March 13, 2009). "A look at ftrace". LWN.net. Retrieved July 23, 2014. <a href="https://lwn.net/Articles/322666/" target="_blank">https://lwn.net/Articles/322666/</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Steven Rostedt (June 16, 2014). "Linux kernel documentation: Documentation/trace/ftrace.txt". kernel.org. Retrieved July 23, 2014. <a href="https://www.kernel.org/doc/Documentation/trace/ftrace.txt" target="_blank">https://www.kernel.org/doc/Documentation/trace/ftrace.txt</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>"Red Hat Enterprise Linux 6 documentation, Section 6.5. ftrace". Red Hat. March 14, 2014. Retrieved July 23, 2014. <a href="https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Developer_Guide/ftrace.html" target="_blank">https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Developer_Guide/ftrace.html</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Jake Edge (March 13, 2009). "A look at ftrace". LWN.net. Retrieved July 23, 2014. <a href="https://lwn.net/Articles/322666/" target="_blank">https://lwn.net/Articles/322666/</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Steven Rostedt (October 18, 2010). "Ftrace: Linux Kernel Tracing" (PDF). linuxfoundation.org. Archived from the original (PDF) on March 8, 2013. Retrieved July 23, 2014. <a href="https://web.archive.org/web/20130308164230/http://events.linuxfoundation.org/slides/2010/linuxcon_japan/linuxcon_jp2010_rostedt.pdf" target="_blank">https://web.archive.org/web/20130308164230/http://events.linuxfoundation.org/slides/2010/linuxcon_japan/linuxcon_jp2010_rostedt.pdf</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Steven Rostedt (October 20, 2010). "trace-cmd: A front-end for Ftrace". LWN.net. Retrieved January 19, 2015. <a href="https://lwn.net/Articles/410200/" target="_blank">https://lwn.net/Articles/410200/</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>Steven Rostedt (February 2, 2011). "Using KernelShark to analyze the real-time scheduler". LWN.net. Retrieved June 11, 2016. <a href="https://lwn.net/Articles/425583/" target="_blank">https://lwn.net/Articles/425583/</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>Steven Rostedt (January 5, 2015). "Ftrace Kernel Hooks: More than just tracing" (PDF). linuxplumbersconf.org. pp. 6–12, 24, 34, 56–58. Retrieved June 11, 2016. <a href="http://www.linuxplumbersconf.org/2014/ocw/system/presentations/1773/original/ftrace-kernel-hooks-2014.pdf" target="_blank">http://www.linuxplumbersconf.org/2014/ocw/system/presentations/1773/original/ftrace-kernel-hooks-2014.pdf</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>Tim Bird (November 1, 2012). "Measuring Function Duration with Ftrace" (PDF). elinux.org. pp. 5–6, 12–14. Retrieved June 11, 2016. <a href="http://elinux.org/images/d/d6/Measuring-function-duration-with-ftrace.pdf" target="_blank">http://elinux.org/images/d/d6/Measuring-function-duration-with-ftrace.pdf</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>"Linux kernel 2.6.27, Section 1.7. ftrace, sysprof support". kernelnewbies.org. October 9, 2008. Retrieved July 23, 2014. <a href="http://kernelnewbies.org/Linux_2_6_27#head-27c23aa79ee6da975ef95b4fff381ace1667a264" target="_blank">http://kernelnewbies.org/Linux_2_6_27#head-27c23aa79ee6da975ef95b4fff381ace1667a264</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> </ol>