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There are some code paths in the kernel that need to do some preparations
before it calls a tracepoint. As that code is worthless overhead when
the tracepoint is not enabled, it would be prudent to have that code
only run when the tracepoint is active. To accomplish this, all tracepoints
now get a static inline function called "trace_<tracepoint-name>_enabled()"
which returns true when the tracepoint is enabled and false otherwise.
As an added bonus, that function uses the static_key of the tracepoint
such that no branch is needed.
if (trace_mytracepoint_enabled()) {
arg = process_tp_arg();
trace_mytracepoint(arg);
}
Will keep the "process_tp_arg()" (which may be expensive to run) from
being executed when the tracepoint isn't enabled.
It's best to encapsulate the tracepoint itself in the if statement
just to keep races. For example, if you had:
if (trace_mytracepoint_enabled())
arg = process_tp_arg();
trace_mytracepoint(arg);
There's a chance that the tracepoint could be enabled just after the
if statement, and arg will be undefined when calling the tracepoint.
Link: http://lkml.kernel.org/r/20140506094407.507b6435@gandalf.local.home
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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Existing tracepoint documentation doesn't mention the popular
TRACE_EVENT macro. Since an excellent series of articles on proper
usage already exists, respective links are added to the existing
documentation.
Signed-off-by: Stefan Raspl <raspl@linux.vnet.ibm.com>
Cc: Rob Landley <rob@landley.net>
Cc: Jiri Kosina <jkosina@suse.cz>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Zoltan Kiss <zoltan.kiss@citrix.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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The sample missed the moving of the header files into the events subdirectory.
I've also extended it based on the existing headers, and mentioned the tiny
but important role of CREATE_TRACE_POINTS.
Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
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The tracepoint sample code got removed. Remove a few lines on its usage
too.
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: Rob Landley <rob@landley.net>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
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Move kmemtrace.txt, tracepoints.txt, ftrace.txt and mmiotrace.txt to
the new trace/ directory.
I didnt find any references to those documents in both source
files and documents, so no extra work needs to be done.
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Pekka Paalanen <pq@iki.fi>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
LKML-Reference: <49DD6E2B.6090200@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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