diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/trace/ftrace.txt | 26 | ||||
| -rw-r--r-- | Documentation/trace/tracepoints.txt | 24 |
2 files changed, 50 insertions, 0 deletions
diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt index bd365988e8d8..2479b2a0c77c 100644 --- a/Documentation/trace/ftrace.txt +++ b/Documentation/trace/ftrace.txt @@ -2003,6 +2003,32 @@ want, depending on your needs. 360.774530 | 1) 0.594 us | __phys_addr(); +The function name is always displayed after the closing bracket +for a function if the start of that function is not in the +trace buffer. + +Display of the function name after the closing bracket may be +enabled for functions whose start is in the trace buffer, +allowing easier searching with grep for function durations. +It is default disabled. + + hide: echo nofuncgraph-tail > trace_options + show: echo funcgraph-tail > trace_options + + Example with nofuncgraph-tail (default): + 0) | putname() { + 0) | kmem_cache_free() { + 0) 0.518 us | __phys_addr(); + 0) 1.757 us | } + 0) 2.861 us | } + + Example with funcgraph-tail: + 0) | putname() { + 0) | kmem_cache_free() { + 0) 0.518 us | __phys_addr(); + 0) 1.757 us | } /* kmem_cache_free() */ + 0) 2.861 us | } /* putname() */ + You can put some comments on specific functions by using trace_printk() For example, if you want to put a comment inside the __might_sleep() function, you just have to include diff --git a/Documentation/trace/tracepoints.txt b/Documentation/trace/tracepoints.txt index 6b018b53177a..a3efac621c5a 100644 --- a/Documentation/trace/tracepoints.txt +++ b/Documentation/trace/tracepoints.txt @@ -115,6 +115,30 @@ If the tracepoint has to be used in kernel modules, an EXPORT_TRACEPOINT_SYMBOL_GPL() or EXPORT_TRACEPOINT_SYMBOL() can be 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: + + if (trace_foo_bar_enabled()) { + int i; + int tot = 0; + + for (i = 0; i < count; i++) + tot += calculate_nuggets(); + + trace_foo_bar(tot); + } + +All trace_<tracepoint>() 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 +block of the if (trace_<tracepoint>_enabled()) to prevent races between +the tracepoint being enabled and the check being seen. + +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 define tracepoints. Check http://lwn.net/Articles/379903, http://lwn.net/Articles/381064 and http://lwn.net/Articles/383362 |