sched/rt: Support sched_stat_runtime tracepoint for RT sched class

The runtime of a RT task has already been there, so we only need to
add a tracepoint.

One difference between fair task and RT task is that there is no vruntime
in RT task. To reuse the sched_stat_runtime tracepoint, '0' is passed as
vruntime for RT task.

The output of this tracepoint for RT task as follows,
          stress-9748    [039] d.h.   113.519352: sched_stat_runtime: comm=stress pid=9748 runtime=997573 [ns] vruntime=0 [ns]
          stress-9748    [039] d.h.   113.520352: sched_stat_runtime: comm=stress pid=9748 runtime=997627 [ns] vruntime=0 [ns]
          stress-9748    [039] d.h.   113.521352: sched_stat_runtime: comm=stress pid=9748 runtime=998203 [ns] vruntime=0 [ns]

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210905143547.4668-6-laoar.shao@gmail.com

kernel/sched/rt.c

@@ -1012,6 +1012,8 @@ static void update_curr_rt(struct rq *rq)
 	schedstat_set(curr->stats.exec_max,
 		      max(curr->stats.exec_max, delta_exec));
 
+	trace_sched_stat_runtime(curr, delta_exec, 0);
+
 	curr->se.sum_exec_runtime += delta_exec;
 	account_group_exec_runtime(curr, delta_exec);