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Message-ID: <172396218984.2215.18280492377096522742.tip-bot2@tip-bot2>
Date: Sun, 18 Aug 2024 06:23:09 -0000
From: "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Luis Machado <luis.machado@....com>, Hongyan Xia <hongyan.xia2@....com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Valentin Schneider <vschneid@...hat.com>, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched/uclamg: Handle delayed dequeue
The following commit has been merged into the sched/core branch of tip:
Commit-ID: dfa0a574cbc47bfd5f8985f74c8ea003a37fa078
Gitweb: https://git.kernel.org/tip/dfa0a574cbc47bfd5f8985f74c8ea003a37fa078
Author: Peter Zijlstra <peterz@...radead.org>
AuthorDate: Wed, 05 Jun 2024 12:09:11 +02:00
Committer: Peter Zijlstra <peterz@...radead.org>
CommitterDate: Sat, 17 Aug 2024 11:06:42 +02:00
sched/uclamg: Handle delayed dequeue
Delayed dequeue has tasks sit around on the runqueue that are not
actually runnable -- specifically, they will be dequeued the moment
they get picked.
One side-effect is that such a task can get migrated, which leads to a
'nested' dequeue_task() scenario that messes up uclamp if we don't
take care.
Notably, dequeue_task(DEQUEUE_SLEEP) can 'fail' and keep the task on
the runqueue. This however will have removed the task from uclamp --
per uclamp_rq_dec() in dequeue_task(). So far so good.
However, if at that point the task gets migrated -- or nice adjusted
or any of a myriad of operations that does a dequeue-enqueue cycle --
we'll pass through dequeue_task()/enqueue_task() again. Without
modification this will lead to a double decrement for uclamp, which is
wrong.
Reported-by: Luis Machado <luis.machado@....com>
Reported-by: Hongyan Xia <hongyan.xia2@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Valentin Schneider <vschneid@...hat.com>
Tested-by: Valentin Schneider <vschneid@...hat.com>
Link: https://lkml.kernel.org/r/20240727105029.315205425@infradead.org
---
kernel/sched/core.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7356464..80e639e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1691,6 +1691,9 @@ static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p)
if (unlikely(!p->sched_class->uclamp_enabled))
return;
+ if (p->se.sched_delayed)
+ return;
+
for_each_clamp_id(clamp_id)
uclamp_rq_inc_id(rq, p, clamp_id);
@@ -1715,6 +1718,9 @@ static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
if (unlikely(!p->sched_class->uclamp_enabled))
return;
+ if (p->se.sched_delayed)
+ return;
+
for_each_clamp_id(clamp_id)
uclamp_rq_dec_id(rq, p, clamp_id);
}
@@ -1994,8 +2000,12 @@ void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
psi_enqueue(p, (flags & ENQUEUE_WAKEUP) && !(flags & ENQUEUE_MIGRATED));
}
- uclamp_rq_inc(rq, p);
p->sched_class->enqueue_task(rq, p, flags);
+ /*
+ * Must be after ->enqueue_task() because ENQUEUE_DELAYED can clear
+ * ->sched_delayed.
+ */
+ uclamp_rq_inc(rq, p);
if (sched_core_enabled(rq))
sched_core_enqueue(rq, p);
@@ -2017,6 +2027,10 @@ inline bool dequeue_task(struct rq *rq, struct task_struct *p, int flags)
psi_dequeue(p, flags & DEQUEUE_SLEEP);
}
+ /*
+ * Must be before ->dequeue_task() because ->dequeue_task() can 'fail'
+ * and mark the task ->sched_delayed.
+ */
uclamp_rq_dec(rq, p);
return p->sched_class->dequeue_task(rq, p, flags);
}
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