sched: Allow SCHED_BATCH to preempt SCHED_IDLE tasks

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@linux.intel.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Mike Galbraith <efault@gmx.de>
Cc: Richard Purdie <richard.purdie@linuxfoundation.org>
LKML-Reference: <1298408674-3130-2-git-send-email-dvhart@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 7 insertions, 5 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 3a88dee165c0..1438e13cf8be 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1870,16 +1870,18 @@ 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;