Commit 6249687f authored Sep 19, 2011 by Steven Rostedt Committed by Steven Rostedt Sep 19, 2011

tracing: Add a counter clock for those that do not trust clocks



When debugging tight race conditions, it can be helpful to have a
synchronized tracing method. Although in most cases the global clock
provides this functionality, if timings is not the issue, it is more
comforting to know that the order of events really happened in a precise
order.

Instead of using a clock, add a "counter" that is simply an incrementing
atomic 64bit counter that orders the events as they are perceived to
happen.

The trace_clock_counter() is added from the attempt by Peter Zijlstra
trying to convert the trace_clock_global() to it. I took Peter's counter
code and made trace_clock_counter() instead, and added it to the choice
of clocks. Just echo counter > /debug/tracing/trace_clock to activate
it.

Requested-by: Thomas Gleixner <tglx@linutronix.de>
Requested-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-By: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

parent c64e148a

include/linux/trace_clock.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -15,5 +15,6 @@
		extern u64 notrace trace_clock_local(void);
		extern u64 notrace trace_clock(void);
		extern u64 notrace trace_clock_global(void);
		extern u64 notrace trace_clock_counter(void);

		#endif /* _LINUX_TRACE_CLOCK_H */

kernel/trace/trace.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -435,6 +435,7 @@ static struct {
		} trace_clocks[] = {
		{ trace_clock_local, "local" },
		{ trace_clock_global, "global" },
		{ trace_clock_counter, "counter" },
		};

		int trace_clock_id;

kernel/trace/trace_clock.c

+12 −0

Original line number	Diff line number	Diff line
		@@ -113,3 +113,15 @@ u64 notrace trace_clock_global(void)

		return now;
		}

		static atomic64_t trace_counter;

		/*
		* trace_clock_counter(): simply an atomic counter.
		* Use the trace_counter "counter" for cases where you do not care
		* about timings, but are interested in strict ordering.
		*/
		u64 notrace trace_clock_counter(void)
		{
		return atomic64_add_return(1, &trace_counter);
		}

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