sched: Remove resetting exec_start in put_prev_task_rt()

There's no reason to clean the exec_start in put_prev_task_rt() as it is reset
when the task gets back to the run queue. This saves us doing a store() in the
fast path.

Signed-off-by: Hillf Danton <dhillf@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Yong Zhang <yong.zhang0@gmail.com>
Link: http://lkml.kernel.org/r/BANLkTimqWD=q6YnSDi-v9y=LMWecgEzEWg@mail.gmail.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched_rt.c

@@ -1178,7 +1178,6 @@ static struct task_struct *pick_next_task_rt(struct rq *rq)
 static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
 {
 	update_curr_rt(rq);
-	p->se.exec_start = 0;
 
 	/*
 	 * The previous task needs to be made eligible for pushing