[for-next][PATCH 18/20] tracing: Add "uptime" trace clock that uses jiffies

[Steven Rostedt]

From: "Steven Rostedt (Red Hat)" <rostedt@xxxxxxxxxxx>

Add a simple trace clock called "uptime" for those that are
interested in the uptime of the trace. It uses jiffies as that's
the safest method, as other uptime clocks grab seq locks, which could
cause a deadlock if taken from an event or function tracer.

Requested-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 include/linux/trace_clock.h |    1 +
 kernel/trace/trace.c        |    1 +
 kernel/trace/trace_clock.c  |   10 ++++++++++
 3 files changed, 12 insertions(+)

diff --git a/include/linux/trace_clock.h b/include/linux/trace_clock.h
index d563f37..1d7ca27 100644
--- a/include/linux/trace_clock.h
+++ b/include/linux/trace_clock.h
@@ -16,6 +16,7 @@
 
 extern u64 notrace trace_clock_local(void);
 extern u64 notrace trace_clock(void);
+extern u64 notrace trace_clock_jiffies(void);
 extern u64 notrace trace_clock_global(void);
 extern u64 notrace trace_clock_counter(void);
 
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index f90ca16..8eabfbb 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -647,6 +647,7 @@ static struct {
 	{ trace_clock_local,	"local",	1 },
 	{ trace_clock_global,	"global",	1 },
 	{ trace_clock_counter,	"counter",	0 },
+	{ trace_clock_jiffies,	"uptime",	1 },
 	ARCH_TRACE_CLOCKS
 };
 
diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c
index aa8f5f4..26dc348 100644
--- a/kernel/trace/trace_clock.c
+++ b/kernel/trace/trace_clock.c
@@ -57,6 +57,16 @@ u64 notrace trace_clock(void)
 	return local_clock();
 }
 
+/*
+ * trace_jiffy_clock(): Simply use jiffies as a clock counter.
+ */
+u64 notrace trace_clock_jiffies(void)
+{
+	u64 jiffy = jiffies - INITIAL_JIFFIES;
+
+	/* Return nsecs */
+	return (u64)jiffies_to_usecs(jiffy) * 1000ULL;
+}
 
 /*
  * trace_clock_global(): special globally coherent trace clock
-- 
1.7.10.4

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