From: tip-bot for Davidlohr Bueso <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: mingo@kernel.org, linux-kernel@vger.kernel.org,
longman@redhat.com, akpm@linux-foundation.org, dave@stgolabs.net,
peterz@infradead.org, tglx@linutronix.de, will.deacon@arm.com,
elohimes@gmail.com, dbueso@suse.de, hpa@zytor.com,
paulmck@linux.vnet.ibm.com, torvalds@linux-foundation.org
Subject: [tip:locking/core] sched/wake_q: Add branch prediction hint to wake_q_add() cmpxchg
Date: Mon, 21 Jan 2019 03:28:53 -0800 [thread overview]
Message-ID: <tip-87ff19cb2f1aa55a5d8b691e6690cc059a59d2ec@git.kernel.org> (raw)
In-Reply-To: <20181203053130.gwkw6kg72azt2npb@linux-r8p5>
Commit-ID: 87ff19cb2f1aa55a5d8b691e6690cc059a59d2ec
Gitweb: https://git.kernel.org/tip/87ff19cb2f1aa55a5d8b691e6690cc059a59d2ec
Author: Davidlohr Bueso <dave@stgolabs.net>
AuthorDate: Sun, 2 Dec 2018 21:31:30 -0800
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 21 Jan 2019 11:18:50 +0100
sched/wake_q: Add branch prediction hint to wake_q_add() cmpxchg
The cmpxchg() will fail when the task is already in the process
of waking up, and as such is an extremely rare occurrence.
Micro-optimize the call and put an unlikely() around it.
To no surprise, when using CONFIG_PROFILE_ANNOTATED_BRANCHES
under a number of workloads the incorrect rate was a mere 1-2%.
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Yongji Xie <elohimes@gmail.com>
Cc: andrea.parri@amarulasolutions.com
Cc: lilin24@baidu.com
Cc: liuqi16@baidu.com
Cc: nixun@baidu.com
Cc: xieyongji@baidu.com
Cc: yuanlinsi01@baidu.com
Cc: zhangyu31@baidu.com
Link: https://lkml.kernel.org/r/20181203053130.gwkw6kg72azt2npb@linux-r8p5
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/sched/core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d8d76a65cfdd..b05eef7d7a1f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -421,7 +421,7 @@ void wake_q_add(struct wake_q_head *head, struct task_struct *task)
* state, even in the failed case, an explicit smp_mb() must be used.
*/
smp_mb__before_atomic();
- if (cmpxchg_relaxed(&node->next, NULL, WAKE_Q_TAIL))
+ if (unlikely(cmpxchg_relaxed(&node->next, NULL, WAKE_Q_TAIL)))
return;
get_task_struct(task);
next prev parent reply other threads:[~2019-01-21 11:29 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-29 12:50 [RFC] locking/rwsem: Avoid issuing wakeup before setting the reader waiter to nil Yongji Xie
2018-11-29 13:12 ` Peter Zijlstra
2018-11-29 13:44 ` Peter Zijlstra
2018-11-29 14:02 ` Yongji Xie
2018-11-29 18:43 ` Davidlohr Bueso
2018-11-29 18:49 ` Waiman Long
2018-11-29 15:21 ` Waiman Long
2018-11-29 15:29 ` Waiman Long
2018-11-29 16:06 ` Peter Zijlstra
2018-11-29 17:02 ` Waiman Long
2018-11-29 17:27 ` Peter Zijlstra
2018-11-29 17:58 ` Waiman Long
2018-11-29 18:13 ` Peter Zijlstra
2018-11-29 18:17 ` Davidlohr Bueso
2018-11-29 18:08 ` Peter Zijlstra
2018-11-29 18:26 ` Waiman Long
2018-11-29 18:31 ` Will Deacon
2018-11-29 18:34 ` Waiman Long
2018-11-29 22:05 ` Peter Zijlstra
2018-11-30 9:34 ` 答复: " Liu,Qi(ACU-T1)
2018-11-30 14:15 ` Peter Zijlstra
2018-11-29 21:30 ` Davidlohr Bueso
2018-11-29 21:34 ` Davidlohr Bueso
2018-11-29 22:17 ` Peter Zijlstra
2018-11-30 9:30 ` Andrea Parri
2018-12-03 5:31 ` [PATCH -tip] kernel/sched,wake_q: Branch predict wake_q_add() cmpxchg Davidlohr Bueso
2018-12-03 16:10 ` Waiman Long
2019-01-21 11:28 ` tip-bot for Davidlohr Bueso [this message]
2018-12-10 15:12 ` [RFC] locking/rwsem: Avoid issuing wakeup before setting the reader waiter to nil Yongji Xie
2018-12-17 11:37 ` Peter Zijlstra
2018-12-17 13:12 ` Yongji Xie
2019-01-07 14:35 ` Waiman Long
2019-01-07 15:31 ` Peter Zijlstra
2019-01-07 15:35 ` Waiman Long
2018-12-17 20:53 ` Davidlohr Bueso
2018-12-18 13:10 ` Peter Zijlstra
2018-12-18 13:14 ` Peter Zijlstra
2018-12-18 17:27 ` Davidlohr Bueso
2018-12-18 18:54 ` [PATCH v2] sched/wake_q: Reduce reference counting for special users Davidlohr Bueso
2018-12-18 19:17 ` Waiman Long
2018-12-18 19:30 ` Davidlohr Bueso
2018-12-18 19:39 ` Davidlohr Bueso
2018-12-18 19:53 ` [PATCH v4] " Davidlohr Bueso
2018-12-18 20:35 ` Waiman Long
2019-01-21 16:02 ` Davidlohr Bueso
2019-01-22 8:55 ` Peter Zijlstra
2019-02-04 8:57 ` [tip:locking/core] " tip-bot for Davidlohr Bueso
2019-02-07 19:30 ` Davidlohr Bueso
2019-02-12 14:14 ` Daniel Vacek
2019-01-21 11:28 ` [tip:locking/core] locking/rwsem: Fix (possible) missed wakeup tip-bot for Xie Yongji
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