Messages in this thread | | | Date | Thu, 02 Dec 2010 17:36:54 -0500 | From | Steven Rostedt <> | Subject | [RFC][PATCH 0/2] tracing: Add conditional to tracepoints |
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This is an RFC that adds the TP_CONDITION() to the TRACE_EVENT() code.
There are certain cases that a tracepoint only makes sense if a specific condition is met. But because we do not want to dirty the fast path (the non tracing case) with if statements that are there only to avoid tracing, we just pass the condition variables to the tracepoint, and let the user filter them out if needed.
A perfect example is the tracepoint sched_wakeup. It traces all calls to try_to_wake_up() even if it fails to wake up. But if we add:
if (success) trace_sched_wakeup(p);
We have that "if (success)" tested for every time we call try_to_wake_up(). Even when tracing is not (or never will be) enabled.
This patch set adds a variant TRACE_EVENT_CONDITIONAL() (and DECLARE_EVENT_CLASS_CONDITIONAL()) that has a "cond" argument. This argument is encapsulated with "TP_CONDITIONAL()" which turns into:
if (!cond) return;
This is placed inside the called tracepoint routine, and is only tested when the trace is enabled. Otherwise it is a nop as tracepoints normally are when disabled.
Note, another variant of this, is to move the test directly into the _DO_TRACE() macro, and not call any registered event callbacks. This would even speed it up faster when tracing is enabled. I did not do this orginially because I just thought of it now as I wrote this change log ;-) I'm posting this version now just in case people prefer it instead.
The following patches are in:
git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git
branch: rfc/trace-conditional
Steven Rostedt (2): tracing: Add TRACE_EVENT_CONDITIONAL() tracing: Only trace sched_wakeup if it actually work something up
---- include/linux/tracepoint.h | 3 ++ include/trace/define_trace.h | 6 +++ include/trace/events/sched.h | 12 +++--- include/trace/ftrace.h | 70 +++++++++++++++++++++++++++++++---------- 4 files changed, 68 insertions(+), 23 deletions(-)
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