trace doc: convert trace/tracepoints.txt to rst format
This converts the plain text documentation to reStructuredText format and add it into Sphinx TOC tree. No essential content change. Cc: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Changbin Du <changbin.du@intel.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>hifive-unleashed-5.1
Changbin Du
Jonathan Corbet
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00b27da349
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837e716de2
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@ -11,3 +11,4 @@ Linux Tracing Technologies
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ftrace-uses
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kprobetrace
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uprobetracer
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tracepoints
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@ -1,6 +1,8 @@
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Using the Linux Kernel Tracepoints
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==================================
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Using the Linux Kernel Tracepoints
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==================================
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Mathieu Desnoyers
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:Author: Mathieu Desnoyers
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This document introduces Linux Kernel Tracepoints and their use. It
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@ -9,8 +11,8 @@ connect probe functions to them and provides some examples of probe
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functions.
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* Purpose of tracepoints
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Purpose of tracepoints
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----------------------
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A tracepoint placed in code provides a hook to call a function (probe)
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that you can provide at runtime. A tracepoint can be "on" (a probe is
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connected to it) or "off" (no probe is attached). When a tracepoint is
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@ -31,8 +33,8 @@ header file.
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They can be used for tracing and performance accounting.
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* Usage
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Usage
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-----
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Two elements are required for tracepoints :
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- A tracepoint definition, placed in a header file.
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@ -40,52 +42,53 @@ Two elements are required for tracepoints :
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In order to use tracepoints, you should include linux/tracepoint.h.
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In include/trace/events/subsys.h :
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In include/trace/events/subsys.h::
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#undef TRACE_SYSTEM
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#define TRACE_SYSTEM subsys
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#undef TRACE_SYSTEM
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#define TRACE_SYSTEM subsys
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#if !defined(_TRACE_SUBSYS_H) || defined(TRACE_HEADER_MULTI_READ)
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#define _TRACE_SUBSYS_H
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#if !defined(_TRACE_SUBSYS_H) || defined(TRACE_HEADER_MULTI_READ)
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#define _TRACE_SUBSYS_H
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#include <linux/tracepoint.h>
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#include <linux/tracepoint.h>
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DECLARE_TRACE(subsys_eventname,
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TP_PROTO(int firstarg, struct task_struct *p),
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TP_ARGS(firstarg, p));
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DECLARE_TRACE(subsys_eventname,
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TP_PROTO(int firstarg, struct task_struct *p),
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TP_ARGS(firstarg, p));
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#endif /* _TRACE_SUBSYS_H */
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#endif /* _TRACE_SUBSYS_H */
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/* This part must be outside protection */
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#include <trace/define_trace.h>
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/* This part must be outside protection */
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#include <trace/define_trace.h>
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In subsys/file.c (where the tracing statement must be added) :
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In subsys/file.c (where the tracing statement must be added)::
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#include <trace/events/subsys.h>
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#include <trace/events/subsys.h>
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#define CREATE_TRACE_POINTS
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DEFINE_TRACE(subsys_eventname);
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#define CREATE_TRACE_POINTS
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DEFINE_TRACE(subsys_eventname);
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void somefct(void)
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{
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...
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trace_subsys_eventname(arg, task);
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...
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}
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void somefct(void)
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{
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...
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trace_subsys_eventname(arg, task);
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...
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}
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Where :
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- subsys_eventname is an identifier unique to your event
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- subsys_eventname is an identifier unique to your event
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- subsys is the name of your subsystem.
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- eventname is the name of the event to trace.
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- TP_PROTO(int firstarg, struct task_struct *p) is the prototype of the
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function called by this tracepoint.
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- `TP_PROTO(int firstarg, struct task_struct *p)` is the prototype of the
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function called by this tracepoint.
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- TP_ARGS(firstarg, p) are the parameters names, same as found in the
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prototype.
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- `TP_ARGS(firstarg, p)` are the parameters names, same as found in the
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prototype.
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- if you use the header in multiple source files, #define CREATE_TRACE_POINTS
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should appear only in one source file.
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- if you use the header in multiple source files, `#define CREATE_TRACE_POINTS`
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should appear only in one source file.
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Connecting a function (probe) to a tracepoint is done by providing a
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probe (function to call) for the specific tracepoint through
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@ -117,7 +120,7 @@ used to export the defined tracepoints.
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If you need to do a bit of work for a tracepoint parameter, and
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that work is only used for the tracepoint, that work can be encapsulated
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within an if statement with the following:
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within an if statement with the following::
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if (trace_foo_bar_enabled()) {
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int i;
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@ -139,7 +142,7 @@ The advantage of using the trace_<tracepoint>_enabled() is that it uses
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the static_key of the tracepoint to allow the if statement to be implemented
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with jump labels and avoid conditional branches.
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Note: The convenience macro TRACE_EVENT provides an alternative way to
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.. note:: The convenience macro TRACE_EVENT provides an alternative way to
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define tracepoints. Check http://lwn.net/Articles/379903,
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http://lwn.net/Articles/381064 and http://lwn.net/Articles/383362
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for a series of articles with more details.
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