Commit 837e716d authored by Changbin Du's avatar Changbin Du Committed by Jonathan Corbet

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: default avatarChangbin Du <changbin.du@intel.com>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent 00b27da3
......@@ -11,3 +11,4 @@ Linux Tracing Technologies
ftrace-uses
kprobetrace
uprobetracer
tracepoints
Using the Linux Kernel Tracepoints
==================================
Using the Linux Kernel Tracepoints
==================================
Mathieu Desnoyers
:Author: Mathieu Desnoyers
This document introduces Linux Kernel Tracepoints and their use. It
......@@ -9,8 +11,8 @@ connect probe functions to them and provides some examples of probe
functions.
* Purpose of tracepoints
Purpose of tracepoints
----------------------
A tracepoint placed in code provides a hook to call a function (probe)
that you can provide at runtime. A tracepoint can be "on" (a probe is
connected to it) or "off" (no probe is attached). When a tracepoint is
......@@ -31,8 +33,8 @@ header file.
They can be used for tracing and performance accounting.
* Usage
Usage
-----
Two elements are required for tracepoints :
- A tracepoint definition, placed in a header file.
......@@ -40,52 +42,53 @@ Two elements are required for tracepoints :
In order to use tracepoints, you should include linux/tracepoint.h.
In include/trace/events/subsys.h :
In include/trace/events/subsys.h::
#undef TRACE_SYSTEM
#define TRACE_SYSTEM subsys
#undef TRACE_SYSTEM
#define TRACE_SYSTEM subsys
#if !defined(_TRACE_SUBSYS_H) || defined(TRACE_HEADER_MULTI_READ)
#define _TRACE_SUBSYS_H
#if !defined(_TRACE_SUBSYS_H) || defined(TRACE_HEADER_MULTI_READ)
#define _TRACE_SUBSYS_H
#include <linux/tracepoint.h>
#include <linux/tracepoint.h>
DECLARE_TRACE(subsys_eventname,
TP_PROTO(int firstarg, struct task_struct *p),
TP_ARGS(firstarg, p));
DECLARE_TRACE(subsys_eventname,
TP_PROTO(int firstarg, struct task_struct *p),
TP_ARGS(firstarg, p));
#endif /* _TRACE_SUBSYS_H */
#endif /* _TRACE_SUBSYS_H */
/* This part must be outside protection */
#include <trace/define_trace.h>
/* This part must be outside protection */
#include <trace/define_trace.h>
In subsys/file.c (where the tracing statement must be added) :
In subsys/file.c (where the tracing statement must be added)::
#include <trace/events/subsys.h>
#include <trace/events/subsys.h>
#define CREATE_TRACE_POINTS
DEFINE_TRACE(subsys_eventname);
#define CREATE_TRACE_POINTS
DEFINE_TRACE(subsys_eventname);
void somefct(void)
{
...
trace_subsys_eventname(arg, task);
...
}
void somefct(void)
{
...
trace_subsys_eventname(arg, task);
...
}
Where :
- subsys_eventname is an identifier unique to your event
- subsys_eventname is an identifier unique to your event
- subsys is the name of your subsystem.
- eventname is the name of the event to trace.
- TP_PROTO(int firstarg, struct task_struct *p) is the prototype of the
function called by this tracepoint.
- `TP_PROTO(int firstarg, struct task_struct *p)` is the prototype of the
function called by this tracepoint.
- TP_ARGS(firstarg, p) are the parameters names, same as found in the
prototype.
- `TP_ARGS(firstarg, p)` are the parameters names, same as found in the
prototype.
- if you use the header in multiple source files, #define CREATE_TRACE_POINTS
should appear only in one source file.
- if you use the header in multiple source files, `#define CREATE_TRACE_POINTS`
should appear only in one source file.
Connecting a function (probe) to a tracepoint is done by providing a
probe (function to call) for the specific tracepoint through
......@@ -117,7 +120,7 @@ used to export the defined tracepoints.
If you need to do a bit of work for a tracepoint parameter, and
that work is only used for the tracepoint, that work can be encapsulated
within an if statement with the following:
within an if statement with the following::
if (trace_foo_bar_enabled()) {
int i;
......@@ -139,7 +142,7 @@ The advantage of using the trace_<tracepoint>_enabled() is that it uses
the static_key of the tracepoint to allow the if statement to be implemented
with jump labels and avoid conditional branches.
Note: The convenience macro TRACE_EVENT provides an alternative way to
.. note:: The convenience macro TRACE_EVENT provides an alternative way to
define tracepoints. Check http://lwn.net/Articles/379903,
http://lwn.net/Articles/381064 and http://lwn.net/Articles/383362
for a series of articles with more details.
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