[PATCH 1/2] sched: allow SCHED_BATCH to preempt SCHED_IDLE tasks

[Darren Hart]

Perform the test for SCHED_IDLE before testing for SCHED_BATCH (and ensure idle
tasks don't preempt idle tasks) so the non-interactive, but still important,
SCHED_BATCH tasks will run in favor of the very low priority SCHED_IDLE tasks.

Signed-off-by: Darren Hart <dvhart@xxxxxxxxxxxxxxx>
CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CC: Ingo Molnar <mingo@xxxxxxx>
CC: Richard Purdie <richard.purdie@xxxxxxxxxxxxxxxxxxx>
---
 kernel/sched_fair.c |   12 +++++++-----
 1 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 0c26e2d..ff04bbd 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1857,16 +1857,18 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
 	if (test_tsk_need_resched(curr))
 		return;
 
+	/* Idle tasks are by definition preempted by non-idle tasks. */
+	if (unlikely(curr->policy == SCHED_IDLE) &&
+	    likely(p->policy != SCHED_IDLE))
+		goto preempt;
+
 	/*
-	 * Batch and idle tasks do not preempt (their preemption is driven by
-	 * the tick):
+	 * Batch and idle tasks do not preempt non-idle tasks (their preemption
+	 * is driven by the tick):
 	 */
 	if (unlikely(p->policy != SCHED_NORMAL))
 		return;
 
-	/* Idle tasks are by definition preempted by everybody. */
-	if (unlikely(curr->policy == SCHED_IDLE))
-		goto preempt;
 
 	if (!sched_feat(WAKEUP_PREEMPT))
 		return;
-- 
1.7.1

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