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From: Ingo Molnar <mingo@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Andrew Morton <akpm@linux-foundation.org>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: [GIT PULL] scheduler fix
Date: Sun, 27 Dec 2020 10:16:01 +0100	[thread overview]
Message-ID: <20201227091601.GA1564184@gmail.com> (raw)

Linus,

Please pull the latest sched/urgent git tree from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-urgent-2020-12-27

   # HEAD: ae7927023243dcc7389b2d59b16c09cbbeaecc36 sched: Optimize finish_lock_switch()

Fix a context switch performance regression.

 Thanks,

	Ingo

------------------>
Peter Zijlstra (1):
      sched: Optimize finish_lock_switch()


 kernel/sched/core.c  | 40 +++++++++++++++-------------------------
 kernel/sched/sched.h | 13 +++++--------
 2 files changed, 20 insertions(+), 33 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7af80c3fce12..0ca7d2dc16d5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3985,15 +3985,20 @@ static void do_balance_callbacks(struct rq *rq, struct callback_head *head)
 	}
 }
 
+static void balance_push(struct rq *rq);
+
+struct callback_head balance_push_callback = {
+	.next = NULL,
+	.func = (void (*)(struct callback_head *))balance_push,
+};
+
 static inline struct callback_head *splice_balance_callbacks(struct rq *rq)
 {
 	struct callback_head *head = rq->balance_callback;
 
 	lockdep_assert_held(&rq->lock);
-	if (head) {
+	if (head)
 		rq->balance_callback = NULL;
-		rq->balance_flags &= ~BALANCE_WORK;
-	}
 
 	return head;
 }
@@ -4014,21 +4019,6 @@ static inline void balance_callbacks(struct rq *rq, struct callback_head *head)
 	}
 }
 
-static void balance_push(struct rq *rq);
-
-static inline void balance_switch(struct rq *rq)
-{
-	if (likely(!rq->balance_flags))
-		return;
-
-	if (rq->balance_flags & BALANCE_PUSH) {
-		balance_push(rq);
-		return;
-	}
-
-	__balance_callbacks(rq);
-}
-
 #else
 
 static inline void __balance_callbacks(struct rq *rq)
@@ -4044,10 +4034,6 @@ static inline void balance_callbacks(struct rq *rq, struct callback_head *head)
 {
 }
 
-static inline void balance_switch(struct rq *rq)
-{
-}
-
 #endif
 
 static inline void
@@ -4075,7 +4061,7 @@ static inline void finish_lock_switch(struct rq *rq)
 	 * prev into current:
 	 */
 	spin_acquire(&rq->lock.dep_map, 0, 0, _THIS_IP_);
-	balance_switch(rq);
+	__balance_callbacks(rq);
 	raw_spin_unlock_irq(&rq->lock);
 }
 
@@ -7256,6 +7242,10 @@ static void balance_push(struct rq *rq)
 
 	lockdep_assert_held(&rq->lock);
 	SCHED_WARN_ON(rq->cpu != smp_processor_id());
+	/*
+	 * Ensure the thing is persistent until balance_push_set(.on = false);
+	 */
+	rq->balance_callback = &balance_push_callback;
 
 	/*
 	 * Both the cpu-hotplug and stop task are in this case and are
@@ -7305,9 +7295,9 @@ static void balance_push_set(int cpu, bool on)
 
 	rq_lock_irqsave(rq, &rf);
 	if (on)
-		rq->balance_flags |= BALANCE_PUSH;
+		rq->balance_callback = &balance_push_callback;
 	else
-		rq->balance_flags &= ~BALANCE_PUSH;
+		rq->balance_callback = NULL;
 	rq_unlock_irqrestore(rq, &rf);
 }
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index f5acb6c5ce49..12ada79d40f3 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -975,7 +975,6 @@ struct rq {
 	unsigned long		cpu_capacity_orig;
 
 	struct callback_head	*balance_callback;
-	unsigned char		balance_flags;
 
 	unsigned char		nohz_idle_balance;
 	unsigned char		idle_balance;
@@ -1226,6 +1225,8 @@ struct rq_flags {
 #endif
 };
 
+extern struct callback_head balance_push_callback;
+
 /*
  * Lockdep annotation that avoids accidental unlocks; it's like a
  * sticky/continuous lockdep_assert_held().
@@ -1243,9 +1244,9 @@ static inline void rq_pin_lock(struct rq *rq, struct rq_flags *rf)
 #ifdef CONFIG_SCHED_DEBUG
 	rq->clock_update_flags &= (RQCF_REQ_SKIP|RQCF_ACT_SKIP);
 	rf->clock_update_flags = 0;
-#endif
 #ifdef CONFIG_SMP
-	SCHED_WARN_ON(rq->balance_callback);
+	SCHED_WARN_ON(rq->balance_callback && rq->balance_callback != &balance_push_callback);
+#endif
 #endif
 }
 
@@ -1408,9 +1409,6 @@ init_numa_balancing(unsigned long clone_flags, struct task_struct *p)
 
 #ifdef CONFIG_SMP
 
-#define BALANCE_WORK	0x01
-#define BALANCE_PUSH	0x02
-
 static inline void
 queue_balance_callback(struct rq *rq,
 		       struct callback_head *head,
@@ -1418,13 +1416,12 @@ queue_balance_callback(struct rq *rq,
 {
 	lockdep_assert_held(&rq->lock);
 
-	if (unlikely(head->next || (rq->balance_flags & BALANCE_PUSH)))
+	if (unlikely(head->next || rq->balance_callback == &balance_push_callback))
 		return;
 
 	head->func = (void (*)(struct callback_head *))func;
 	head->next = rq->balance_callback;
 	rq->balance_callback = head;
-	rq->balance_flags |= BALANCE_WORK;
 }
 
 #define rcu_dereference_check_sched_domain(p) \

             reply	other threads:[~2020-12-27  9:22 UTC|newest]

Thread overview: 65+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-27  9:16 Ingo Molnar [this message]
2020-12-27 17:27 ` pr-tracker-bot
  -- strict thread matches above, loose matches on Subject: below --
2021-06-24  7:06 Ingo Molnar
2021-06-24 16:34 ` pr-tracker-bot
2020-03-02  7:51 Ingo Molnar
2020-03-03 23:35 ` pr-tracker-bot
2019-12-17 11:54 Ingo Molnar
2019-12-17 19:20 ` pr-tracker-bot
2019-07-14 10:19 Ingo Molnar
2019-07-14 18:45 ` pr-tracker-bot
2019-05-05 11:02 Ingo Molnar
2019-05-05 22:10 ` pr-tracker-bot
2019-04-27 14:39 Ingo Molnar
2019-04-27 18:45 ` pr-tracker-bot
2019-04-12 13:08 Ingo Molnar
2019-04-13  4:05 ` pr-tracker-bot
2018-12-31 14:58 Ingo Molnar
2018-12-31 18:05 ` pr-tracker-bot
2018-11-17 10:57 Ingo Molnar
2018-11-18 20:05 ` pr-tracker-bot
2018-10-11  9:12 Ingo Molnar
2018-10-11 12:32 ` Greg Kroah-Hartman
2018-10-11  9:02 Ingo Molnar
2018-01-17 15:34 Ingo Molnar
2017-10-27 19:16 Ingo Molnar
2016-12-07 18:48 Ingo Molnar
2016-10-28  8:35 Ingo Molnar
2016-10-19 15:52 Ingo Molnar
2016-10-18 11:17 Ingo Molnar
2016-09-13 18:17 Ingo Molnar
2016-07-14 18:56 Ingo Molnar
2016-05-13 18:54 Ingo Molnar
2016-05-06 11:31 Ingo Molnar
2015-07-18  2:56 Ingo Molnar
2015-03-28 13:45 Ingo Molnar
2014-01-15 18:19 Ingo Molnar
2013-09-28 18:08 Ingo Molnar
2013-09-12 12:58 Ingo Molnar
2012-05-17  8:46 Ingo Molnar
2012-03-02 10:57 Ingo Molnar
2012-02-27 10:29 Ingo Molnar
2011-04-07 17:38 Ingo Molnar
2011-03-18 13:52 Ingo Molnar
2011-03-10  8:01 Ingo Molnar
2011-01-24 13:07 Ingo Molnar
2010-04-08 15:38 Ingo Molnar
2010-04-08 15:42 ` Linus Torvalds
2010-04-08 16:03   ` Andreas Schwab
2010-04-08 18:26     ` Ingo Molnar
2010-04-08 18:36       ` Linus Torvalds
2010-04-08 18:52         ` Ingo Molnar
2009-12-23 16:03 Ingo Molnar
2009-10-08 19:01 Ingo Molnar
2009-05-05  9:35 Ingo Molnar
2009-02-17 16:40 [git pull] " Ingo Molnar
2009-02-04 19:18 Ingo Molnar
2009-01-07 22:26 Ingo Molnar
2009-01-07 23:47 ` Linus Torvalds
2009-01-08  7:50   ` Peter Zijlstra
2008-12-04 19:41 Ingo Molnar
2008-04-14 15:07 Ingo Molnar
2008-01-22 10:33 Ingo Molnar
2007-10-29 20:39 [git pull] scheduler fixes Ingo Molnar
2007-10-29 23:34 ` [git pull] scheduler fix Ingo Molnar
2007-10-30 10:15   ` Guillaume Chazarain
2007-11-01  8:39     ` Ingo Molnar

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