diff options
Diffstat (limited to 'Documentation/trace/tracepoints.rst')
| -rw-r--r-- | Documentation/trace/tracepoints.rst | 19 |
1 files changed, 12 insertions, 7 deletions
diff --git a/Documentation/trace/tracepoints.rst b/Documentation/trace/tracepoints.rst index 0cb8d9ca3d60..b35c40e3abbe 100644 --- a/Documentation/trace/tracepoints.rst +++ b/Documentation/trace/tracepoints.rst @@ -27,7 +27,7 @@ the tracepoint site). You can put tracepoints at important locations in the code. They are lightweight hooks that can pass an arbitrary number of parameters, -which prototypes are described in a tracepoint declaration placed in a +whose prototypes are described in a tracepoint declaration placed in a header file. They can be used for tracing and performance accounting. @@ -71,7 +71,7 @@ In subsys/file.c (where the tracing statement must be added):: void somefct(void) { ... - trace_subsys_eventname(arg, task); + trace_subsys_eventname_tp(arg, task); ... } @@ -129,12 +129,12 @@ within an if statement with the following:: for (i = 0; i < count; i++) tot += calculate_nuggets(); - trace_foo_bar(tot); + trace_foo_bar_tp(tot); } -All trace_<tracepoint>() calls have a matching trace_<tracepoint>_enabled() +All trace_<tracepoint>_tp() calls have a matching trace_<tracepoint>_enabled() function defined that returns true if the tracepoint is enabled and -false otherwise. The trace_<tracepoint>() should always be within the +false otherwise. The trace_<tracepoint>_tp() should always be within the block of the if (trace_<tracepoint>_enabled()) to prevent races between the tracepoint being enabled and the check being seen. @@ -143,7 +143,10 @@ 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 - define tracepoints. Check http://lwn.net/Articles/379903, + define tracepoints. Note, DECLARE_TRACE(foo) creates a function + "trace_foo_tp()" whereas TRACE_EVENT(foo) creates a function + "trace_foo()", and also exposes the tracepoint as a trace event in + /sys/kernel/tracing/events directory. 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. @@ -159,7 +162,9 @@ In a C file:: void do_trace_foo_bar_wrapper(args) { - trace_foo_bar(args); + trace_foo_bar_tp(args); // for tracepoints created via DECLARE_TRACE + // or + trace_foo_bar(args); // for tracepoints created via TRACE_EVENT } In the header file:: |