tracing: Add "uptime" trace clock that uses jiffies

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@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

2 files changed, 11 insertions, 0 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index f90ca16afcf2..8eabfbb8003e 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 aa8f5f48dae6..26dc348332b7 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