This is a note to let you know that I've just added the patch titled
sched/fair: Make SCHED_IDLE entity be preempted in strict hierarchy
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sched-fair-make-sched_idle-entity-be-preempted-in-st.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 053727ebad9a4bdbf21c8bdae2d249a327d7fb76
Author: Tianchen Ding <dtcccc@xxxxxxxxxxxxxxxxx>
Date: Wed Jun 26 10:35:05 2024 +0800
sched/fair: Make SCHED_IDLE entity be preempted in strict hierarchy
[ Upstream commit faa42d29419def58d3c3e5b14ad4037f0af3b496 ]
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 {c,p}se_is_idle only. This makes SCHED_IDLE of
a task a relative policy that is effective only within its own cgroup,
similar to the behavior of NICE.
Also fix se_is_idle() definition when !CONFIG_FAIR_GROUP_SCHED.
Fixes: 304000390f88 ("sched: Cgroup SCHED_IDLE support")
Signed-off-by: Tianchen Ding <dtcccc@xxxxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Josh Don <joshdon@xxxxxxxxxx>
Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20240626023505.1332596-1-dtcccc@xxxxxxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b2e1009e5706e..5fc0d9cc9d9d7 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -533,7 +533,7 @@ 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 */
@@ -8209,16 +8209,7 @@ 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(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);
@@ -8228,7 +8219,7 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
pse_is_idle = se_is_idle(pse);
/*
- * Preempt an idle group in favor of a non-idle group (and don't preempt
+ * Preempt an idle entity in favor of a non-idle entity (and don't preempt
* in the inverse case).
*/
if (cse_is_idle && !pse_is_idle)
@@ -8236,9 +8227,14 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
if (cse_is_idle != pse_is_idle)
return;
+ /*
+ * BATCH and IDLE tasks do not preempt others.
+ */
+ if (unlikely(p->policy != SCHED_NORMAL))
+ return;
+
cfs_rq = cfs_rq_of(se);
update_curr(cfs_rq);
-
/*
* XXX pick_eevdf(cfs_rq) != se ?
*/
