perf_counter: Add PERF_SAMPLE_PERIOD

In order to allow easy tracking of the period, also provide means of
adding it to the sample data.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 9cea32a..6bc2500 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -106,6 +106,7 @@
 	PERF_SAMPLE_CALLCHAIN		= 1U << 5,
 	PERF_SAMPLE_ID			= 1U << 6,
 	PERF_SAMPLE_CPU			= 1U << 7,
+	PERF_SAMPLE_PERIOD		= 1U << 8,
 };
 
 /*
@@ -260,6 +261,7 @@
 	 * struct {
 	 *	struct perf_event_header	header;
 	 *	u64				time;
+	 *	u64				id;
 	 *	u64				sample_period;
 	 * };
 	 */