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From: Waiman Long <longman@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>,
	Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org, linux-xtensa@linux-xtensa.org,
	Davidlohr Bueso <dave@stgolabs.net>,
	linux-ia64@vger.kernel.org, Tim Chen <tim.c.chen@linux.intel.com>,
	Arnd Bergmann <arnd@arndb.de>,
	linux-sh@vger.kernel.org, linux-hexagon@vger.kernel.org,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	linux-kernel@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Borislav Petkov <bp@alien8.de>,
	linux-alpha@vger.kernel.org, sparclinux@vger.kernel.org,
	Waiman Long <longman@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linuxppc-dev@lists.ozlabs.org,
	linux-arm-kernel@lists.infradead.org
Subject: [PATCH-tip 18/22] locking/rwsem: Make rwsem_spin_on_owner() return a tri-state value
Date: Thu,  7 Feb 2019 14:07:22 -0500
Message-ID: <1549566446-27967-19-git-send-email-longman@redhat.com> (raw)
In-Reply-To: <1549566446-27967-1-git-send-email-longman@redhat.com>

This patch modifies rwsem_spin_on_owner() to return a tri-state value
to better reflect the state of lock holder which enables us to make a
better decision of what to do next.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 kernel/locking/rwsem-xadd.c | 25 +++++++++++++++++++------
 kernel/locking/rwsem-xadd.h |  5 +++++
 2 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index 21d462f..0a29aac 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -305,14 +305,24 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
 }
 
 /*
- * Return true only if we can still spin on the owner field of the rwsem.
+ * Return the folowing three values depending on the lock owner state.
+ *   1	when owner changes and no reader is detected yet.
+ *   0	when owner changes and the new owner may be a reader.
+ *  -1	when optimistic spinning has to stop because either the owner stops
+ *	running, is unknown, or its timeslice has been used up.
  */
-static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem)
+enum owner_state {
+	OWNER_SPINNABLE = 1,
+	OWNER_READER = 0,
+	OWNER_NONSPINNABLE = -1,
+};
+
+static noinline enum owner_state rwsem_spin_on_owner(struct rw_semaphore *sem)
 {
 	struct task_struct *owner = rwsem_get_owner(sem);
 
 	if (!is_rwsem_owner_spinnable(owner))
-		return false;
+		return OWNER_NONSPINNABLE;
 
 	rcu_read_lock();
 	/*
@@ -337,7 +347,7 @@ static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem)
 		 */
 		if (need_resched() || !owner_on_cpu(owner, sem)) {
 			rcu_read_unlock();
-			return false;
+			return OWNER_NONSPINNABLE;
 		}
 
 		cpu_relax();
@@ -348,7 +358,10 @@ static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem)
 	 * If there is a new owner or the owner is not set, we continue
 	 * spinning.
 	 */
-	return is_rwsem_owner_spinnable(rwsem_get_owner(sem));
+	owner = rwsem_get_owner(sem);
+	if (!is_rwsem_owner_spinnable(owner))
+		return OWNER_NONSPINNABLE;
+	return is_rwsem_owner_reader(owner) ? OWNER_READER : OWNER_SPINNABLE;
 }
 
 static bool rwsem_optimistic_spin(struct rw_semaphore *sem, const long wlock)
@@ -371,7 +384,7 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem, const long wlock)
 	 *  2) readers own the lock as we can't determine if they are
 	 *     actively running or not.
 	 */
-	while (rwsem_spin_on_owner(sem)) {
+	while (rwsem_spin_on_owner(sem) == OWNER_SPINNABLE) {
 		/*
 		 * Try to acquire the lock
 		 */
diff --git a/kernel/locking/rwsem-xadd.h b/kernel/locking/rwsem-xadd.h
index d54b5db..1de6f1e 100644
--- a/kernel/locking/rwsem-xadd.h
+++ b/kernel/locking/rwsem-xadd.h
@@ -200,6 +200,11 @@ static inline bool is_rwsem_owner_spinnable(struct task_struct *owner)
 	return !((unsigned long)owner & RWSEM_ANONYMOUSLY_OWNED);
 }
 
+static inline bool is_rwsem_owner_reader(struct task_struct *owner)
+{
+	return (unsigned long)owner & RWSEM_READER_OWNED;
+}
+
 /*
  * Return true if the rwsem is owned by a reader.
  */
-- 
1.8.3.1


  parent reply index

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-07 19:07 [PATCH-tip 00/22] locking/rwsem: Rework rwsem-xadd & enable new rwsem features Waiman Long
2019-02-07 19:07 ` [PATCH-tip 01/22] locking/qspinlock_stat: Introduce a generic lockevent counting APIs Waiman Long
2019-02-07 19:07 ` [PATCH-tip 02/22] locking/lock_events: Make lock_events available for all archs & other locks Waiman Long
2019-02-07 19:07 ` [PATCH-tip 03/22] locking/rwsem: Relocate rwsem_down_read_failed() Waiman Long
2019-02-07 19:07 ` [PATCH-tip 04/22] locking/rwsem: Remove arch specific rwsem files Waiman Long
2019-02-07 19:36   ` Peter Zijlstra
2019-02-07 19:43     ` Waiman Long
2019-02-07 19:48     ` Peter Zijlstra
2019-02-07 19:07 ` [PATCH-tip 05/22] locking/rwsem: Move owner setting code from rwsem.c to rwsem.h Waiman Long
2019-02-07 19:07 ` [PATCH-tip 06/22] locking/rwsem: Rename kernel/locking/rwsem.h Waiman Long
2019-02-07 19:07 ` [PATCH-tip 07/22] locking/rwsem: Move rwsem internal function declarations to rwsem-xadd.h Waiman Long
2019-02-07 19:07 ` [PATCH-tip 08/22] locking/rwsem: Add debug check for __down_read*() Waiman Long
2019-02-07 19:07 ` [PATCH-tip 09/22] locking/rwsem: Enhance DEBUG_RWSEMS_WARN_ON() macro Waiman Long
2019-02-07 19:07 ` [PATCH-tip 10/22] locking/rwsem: Enable lock event counting Waiman Long
2019-02-07 19:07 ` [PATCH-tip 11/22] locking/rwsem: Implement a new locking scheme Waiman Long
2019-02-07 19:07 ` [PATCH-tip 12/22] locking/rwsem: Implement lock handoff to prevent lock starvation Waiman Long
2019-02-07 19:07 ` [PATCH-tip 13/22] locking/rwsem: Remove rwsem_wake() wakeup optimization Waiman Long
2019-02-07 19:07 ` [PATCH-tip 14/22] locking/rwsem: Add more rwsem owner access helpers Waiman Long
2019-02-07 19:07 ` [PATCH-tip 15/22] locking/rwsem: Merge owner into count on x86-64 Waiman Long
2019-02-07 19:45   ` Peter Zijlstra
2019-02-07 19:55     ` Waiman Long
2019-02-07 20:08   ` Peter Zijlstra
2019-02-07 20:54     ` Waiman Long
2019-02-08 14:19       ` Waiman Long
2019-02-07 19:07 ` [PATCH-tip 16/22] locking/rwsem: Remove redundant computation of writer lock word Waiman Long
2019-02-07 19:07 ` [PATCH-tip 17/22] locking/rwsem: Recheck owner if it is not on cpu Waiman Long
2019-02-07 19:07 ` Waiman Long [this message]
2019-02-07 19:07 ` [PATCH-tip 19/22] locking/rwsem: Enable readers spinning on writer Waiman Long
2019-02-07 19:07 ` [PATCH-tip 20/22] locking/rwsem: Enable count-based spinning on reader Waiman Long
2019-02-07 19:07 ` [PATCH-tip 21/22] locking/rwsem: Wake up all readers in wait queue Waiman Long
2019-02-07 19:07 ` [PATCH-tip 22/22] locking/rwsem: Ensure an RT task will not spin on reader Waiman Long
2019-02-07 19:51 ` [PATCH-tip 00/22] locking/rwsem: Rework rwsem-xadd & enable new rwsem features Davidlohr Bueso
2019-02-07 20:00   ` Waiman Long
2019-02-11  7:38     ` Ingo Molnar
2019-02-08 19:50 ` Linus Torvalds
2019-02-08 20:31   ` Waiman Long
2019-02-09  0:03     ` Linus Torvalds
2019-02-14 13:23     ` Davidlohr Bueso
2019-02-14 15:22       ` Waiman Long
2019-02-13  9:19 ` Chen Rong
2019-02-13 19:56   ` Linus Torvalds
2019-04-10  8:15     ` huang ying
2019-04-10 16:08       ` Waiman Long
2019-04-12  0:49         ` huang ying

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