kernel/sched/fair.c | 19 ++++++++----------- 1 file changed, 8 insertions(+), 11 deletions(-)
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@linux.alibaba.com>
---
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);
--
2.39.3On Mon, 24 Jun 2024 at 09:39, Tianchen Ding <dtcccc@linux.alibaba.com> wrote:
>
> 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@linux.alibaba.com>
> ---
> 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
Replace "group" by "entity" in the comment above as it is not only
group but also entity
> 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))
I think I would prefer entity_is_task() which makes easier to
understand that the condition is about task
+ if (unlikely(entity_is_task(pse) && p->policy == SCHED_BATCH))
other than the 2 comments above
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
> + return;
>
> cfs_rq = cfs_rq_of(se);
> update_curr(cfs_rq);
> --
> 2.39.3
>
Hi Tianchen, Thanks for these fixes. > #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; nit: add newline > + /* > + * 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; I think it is worth extending that comment to explain why we don't also check policy for SCHED_IDLE here (since the cse_is_idle checks above boil down to checking for task idle policy in this special case where pse is a task entity). The comment above the pse_is_idle checks only talks about idle group preemption, when here we're relying on it for idle task preemption. > > cfs_rq = cfs_rq_of(se); > update_curr(cfs_rq); > -- > 2.39.3 > Reviewed-by: Josh Don <joshdon@google.com>
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