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authorSteven Rostedt <srostedt@redhat.com>2011-09-19 11:35:58 -0400
committerSteven Rostedt <rostedt@goodmis.org>2011-09-19 11:35:58 -0400
commit6249687f76b69cc0b2ad34636f4a18d693ef3262 (patch)
tree9c007b85738eb86f113a9a6de1e35129532e5f54
parentc64e148a3be3cb786534ad38298c25c833116c26 (diff)
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>
-rw-r--r--include/linux/trace_clock.h1
-rw-r--r--kernel/trace/trace.c1
-rw-r--r--kernel/trace/trace_clock.c12
3 files changed, 14 insertions, 0 deletions
diff --git a/include/linux/trace_clock.h b/include/linux/trace_clock.h
index 7a8130384087..4eb490237d4c 100644
--- a/include/linux/trace_clock.h
+++ b/include/linux/trace_clock.h
@@ -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 */
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index b41907000bc6..4b8df0dc9358 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -435,6 +435,7 @@ static struct {
} trace_clocks[] = {
{ trace_clock_local, "local" },
{ trace_clock_global, "global" },
+ { trace_clock_counter, "counter" },
};
int trace_clock_id;
diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c
index 6302747a1398..394783531cbb 100644
--- a/kernel/trace/trace_clock.c
+++ b/kernel/trace/trace_clock.c
@@ -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);
+}