[PATCH] sched/fair: Allow non-idle task to preempt idle task directly

[zhangsong <zhangsong34@huawei.com>]

From: zhangsong <zhangsong34@gmail.com>

In check_preempt_tick(), the sched idle task may exectue at least
`sysctl_sched_min_granularity` time but any other cfs tasks cannot
preempt it. So it is nessesary to ignore the `sysctl_sched_min_granularity`
resctriction for sched idle task preemption.

Signed-off-by: zhangsong <zhangsong34@gmail.com>
---
 kernel/sched/fair.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d4bd299d6..edcb33440 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4477,6 +4477,15 @@ check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
 	struct sched_entity *se;
 	s64 delta;
 
+	se = __pick_first_entity(cfs_rq);
+
+	if ((cfs_rq->last && se_is_idle(cfs_rq->last) - se_is_idle(curr) < 0) ||
+	    (cfs_rq->next && se_is_idle(cfs_rq->last) - se_is_idle(curr) < 0) ||
+	    se_is_idle(se) - se_is_idle(curr) < 0) {
+		resched_curr(rq_of(cfs_rq));
+		return;
+	}
+
 	ideal_runtime = sched_slice(cfs_rq, curr);
 	delta_exec = curr->sum_exec_runtime - curr->prev_sum_exec_runtime;
 	if (delta_exec > ideal_runtime) {
@@ -4497,7 +4506,6 @@ check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
 	if (delta_exec < sysctl_sched_min_granularity)
 		return;
 
-	se = __pick_first_entity(cfs_rq);
 	delta = curr->vruntime - se->vruntime;
 
 	if (delta < 0)
-- 
2.27.0