[PATCH] sched/fair: Make SCHED_IDLE se be preempted in strict hierarchy
From: Tianchen Ding
Date: Mon Jun 24 2024 - 03:39:23 EST
Consider the following cgroup:
root
|
------------------------
| |
normal_cgroup idle_cgroup
| |
SCHED_IDLE task_A SCHED_NORMAL task_B
According to the cgroup hierarchy, A should preempt B. But current
check_preempt_wakeup_fair() treats cgroup se and task separately, so B
will preempt A unexpectedly.
Unify the wakeup logic by {p}se_is_idle only.
Also fix a bug about se_is_idle() definition when
!CONFIG_FAIR_GROUP_SCHED.
Fixes: 304000390f88 ("sched: Cgroup SCHED_IDLE support")
Signed-off-by: Tianchen Ding <dtcccc@xxxxxxxxxxxxxxxxx>
---
kernel/sched/fair.c | 19 ++++++++-----------
1 file changed, 8 insertions(+), 11 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 41b58387023d..c91cfaa7d9ee 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -511,7 +511,7 @@ static int cfs_rq_is_idle(struct cfs_rq *cfs_rq)
static int se_is_idle(struct sched_entity *se)
{
- return 0;
+ return task_has_idle_policy(task_of(se));
}
#endif /* CONFIG_FAIR_GROUP_SCHED */
@@ -8382,16 +8382,7 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
if (test_tsk_need_resched(curr))
return;
- /* Idle tasks are by definition preempted by non-idle tasks. */
- if (unlikely(task_has_idle_policy(curr)) &&
- likely(!task_has_idle_policy(p)))
- goto preempt;
-
- /*
- * Batch and idle tasks do not preempt non-idle tasks (their preemption
- * is driven by the tick):
- */
- if (unlikely(p->policy != SCHED_NORMAL) || !sched_feat(WAKEUP_PREEMPTION))
+ if (!sched_feat(WAKEUP_PREEMPTION))
return;
find_matching_se(&se, &pse);
@@ -8408,6 +8399,12 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
goto preempt;
if (cse_is_idle != pse_is_idle)
return;
+ /*
+ * Batch tasks do not preempt non-idle tasks (their preemption
+ * is driven by the tick):
+ */
+ if (unlikely(pse == &p->se && p->policy == SCHED_BATCH))
+ return;
cfs_rq = cfs_rq_of(se);
update_curr(cfs_rq);
--
2.39.3