events, sched: Add tracepoint for accounting blocked time

This tracepoint shows how long a task is sleeping in uninterruptible state.

E.g. it may show how long and where a mutex is waited for.
Signed-off-by: Andrew Vagin <avagin@openvz.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1322471015-107825-8-git-send-email-avagin@openvz.orgSigned-off-by: Ingo Molnar <mingo@elte.hu>

include/trace/events/sched.h

@@ -330,6 +330,13 @@ DEFINE_EVENT(sched_stat_template, sched_stat_iowait,
 	     TP_PROTO(struct task_struct *tsk, u64 delay),
 	     TP_ARGS(tsk, delay));
 
+/*
+ * Tracepoint for accounting blocked time (time the task is in uninterruptible).
+ */
+DEFINE_EVENT(sched_stat_template, sched_stat_blocked,
+	     TP_PROTO(struct task_struct *tsk, u64 delay),
+	     TP_ARGS(tsk, delay));
+
 /*
  * Tracepoint for accounting runtime (time the task is executing
  * on a CPU).

kernel/sched/fair.c

@@ -1030,6 +1030,8 @@ static void enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se)
 				trace_sched_stat_iowait(tsk, delta);
 			}
 
+			trace_sched_stat_blocked(tsk, delta);
+
 			/*
 			 * Blocking time is in units of nanosecs, so shift by
 			 * 20 to get a milliseconds-range estimation of the