sched/deadline: Make GRUB a task's flag

This patch introduces the SCHED_FLAG_RECLAIM flag to specify
that a DL task is allowed to reclaim unused CPU time (using
the GRUB algorithm).

Tested-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Luca Abeni <luca.abeni@santannapisa.it>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Claudio Scordino <claudio@evidence.eu.com>
Cc: Joel Fernandes <joelaf@google.com>
Cc: Juri Lelli <juri.lelli@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tommaso Cucinotta <tommaso.cucinotta@sssup.it>
Link: http://lkml.kernel.org/r/1495138417-6203-7-git-send-email-luca.abeni@santannapisa.it
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/uapi/linux/sched.h

@@ -47,5 +47,6 @@
  * For the sched_{set,get}attr() calls
  */
 #define SCHED_FLAG_RESET_ON_FORK	0x01
+#define SCHED_FLAG_RECLAIM		0x02
 
 #endif /* _UAPI_LINUX_SCHED_H */

kernel/sched/core.c

@@ -4195,7 +4195,8 @@ recheck:
 			return -EINVAL;
 	}
 
-	if (attr->sched_flags & ~(SCHED_FLAG_RESET_ON_FORK))
+	if (attr->sched_flags &
+		~(SCHED_FLAG_RESET_ON_FORK | SCHED_FLAG_RECLAIM))
 		return -EINVAL;
 
 	/*

kernel/sched/deadline.c

@@ -985,7 +985,8 @@ static void update_curr_dl(struct rq *rq)
 
 	sched_rt_avg_update(rq, delta_exec);
 
-	delta_exec = grub_reclaim(delta_exec, rq);
+	if (unlikely(dl_se->flags & SCHED_FLAG_RECLAIM))
+		delta_exec = grub_reclaim(delta_exec, rq);
 	dl_se->runtime -= delta_exec;
 
 throttle: