events: Move lockless timer calculation into helper function

Take the timer calculation from perf_output_read and move it to a helper
function for any place that needs timer values but cannot take the ctx->lock.

Signed-off-by: Eric B Munson <emunson@mgebm.net>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1308861279-15216-2-git-send-email-emunson@mgebm.net
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/events/core.c

@@ -3351,6 +3351,18 @@ static int perf_event_index(struct perf_event *event)
 	return event->hw.idx + 1 - PERF_EVENT_INDEX_OFFSET;
 }
 
+static void calc_timer_values(struct perf_event *event,
+				u64 *running,
+				u64 *enabled)
+{
+	u64 now, ctx_time;
+
+	now = perf_clock();
+	ctx_time = event->shadow_ctx_time + now;
+	*enabled = ctx_time - event->tstamp_enabled;
+	*running = ctx_time - event->tstamp_running;
+}
+
 /*
  * Callers need to ensure there can be no nesting of this function, otherwise
  * the seqlock logic goes bad. We can not serialize this because the arch
@@ -3816,7 +3828,7 @@ static void perf_output_read_group(struct perf_output_handle *handle,
 static void perf_output_read(struct perf_output_handle *handle,
 			     struct perf_event *event)
 {
-	u64 enabled = 0, running = 0, now, ctx_time;
+	u64 enabled = 0, running = 0;
 	u64 read_format = event->attr.read_format;
 
 	/*
@@ -3828,12 +3840,8 @@ static void perf_output_read(struct perf_output_handle *handle,
 	 * because of locking issue as we are called in
 	 * NMI context
 	 */
-	if (read_format & PERF_FORMAT_TOTAL_TIMES) {
-		now = perf_clock();
-		ctx_time = event->shadow_ctx_time + now;
-		enabled = ctx_time - event->tstamp_enabled;
-		running = ctx_time - event->tstamp_running;
-	}
+	if (read_format & PERF_FORMAT_TOTAL_TIMES)
+		calc_timer_values(event, &enabled, &running);
 
 	if (event->attr.read_format & PERF_FORMAT_GROUP)
 		perf_output_read_group(handle, event, enabled, running);