[PATCH 1/4] MCS Lock: Restructure the MCS lock defines and locking code into its own file
We will need the MCS lock code for doing optimistic spinning for rwsem.
Extracting the MCS code from mutex.c and put into its own file allow us
to reuse this code easily for rwsem.
Reviewed-by: Ingo Molnar
Reviewed-by: Peter Zijlstra
Signed-off-by: Tim Chen
Signed-off-by: Davidlohr Bueso
---
include/linux/mcs_spinlock.h | 64 ++
include/linux/mutex.h|5 ++-
kernel/mutex.c | 60 --
3 files changed, 74 insertions(+), 55 deletions(-)
create mode 100644 include/linux/mcs_spinlock.h
diff --git a/include/linux/mcs_spinlock.h b/include/linux/mcs_spinlock.h
new file mode 100644
index 000..b5de3b0
--- /dev/null
+++ b/include/linux/mcs_spinlock.h
@@ -0,0 +1,64 @@
+/*
+ * MCS lock defines
+ *
+ * This file contains the main data structure and API definitions of MCS lock.
+ *
+ * The MCS lock (proposed by Mellor-Crummey and Scott) is a simple spin-lock
+ * with the desirable properties of being fair, and with each cpu trying
+ * to acquire the lock spinning on a local variable.
+ * It avoids expensive cache bouncings that common test-and-set spin-lock
+ * implementations incur.
+ */
+#ifndef __LINUX_MCS_SPINLOCK_H
+#define __LINUX_MCS_SPINLOCK_H
+
+struct mcs_spinlock {
+ struct mcs_spinlock *next;
+ int locked; /* 1 if lock acquired */
+};
+
+/*
+ * We don't inline mcs_spin_lock() so that perf can correctly account for the
+ * time spent in this lock function.
+ */
+static noinline
+void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
+{
+ struct mcs_spinlock *prev;
+
+ /* Init node */
+ node->locked = 0;
+ node->next = NULL;
+
+ prev = xchg(lock, node);
+ if (likely(prev == NULL)) {
+ /* Lock acquired */
+ node->locked = 1;
+ return;
+ }
+ ACCESS_ONCE(prev->next) = node;
+ smp_wmb();
+ /* Wait until the lock holder passes the lock down */
+ while (!ACCESS_ONCE(node->locked))
+ arch_mutex_cpu_relax();
+}
+
+static void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock
*node)
+{
+ struct mcs_spinlock *next = ACCESS_ONCE(node->next);
+
+ if (likely(!next)) {
+ /*
+* Release the lock by setting it to NULL
+*/
+ if (cmpxchg(lock, node, NULL) == node)
+ return;
+ /* Wait until the next pointer is set */
+ while (!(next = ACCESS_ONCE(node->next)))
+ arch_mutex_cpu_relax();
+ }
+ ACCESS_ONCE(next->locked) = 1;
+ smp_wmb();
+}
+
+#endif /* __LINUX_MCS_SPINLOCK_H */
diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index ccd4260..e6eaeea 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -46,6 +46,7 @@
* - detects multi-task circular deadlocks and prints out all affected
* locks and tasks (and only those tasks)
*/
+struct mcs_spinlock;
struct mutex {
/* 1: unlocked, 0: locked, negative: locked, possible waiters */
atomic_tcount;
@@ -55,7 +56,7 @@ struct mutex {
struct task_struct *owner;
#endif
#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
- void*spin_mlock;/* Spinner MCS lock */
+ struct mcs_spinlock *mcs_lock; /* Spinner MCS lock */
#endif
#ifdef CONFIG_DEBUG_MUTEXES
const char *name;
@@ -179,4 +180,4 @@ extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct
mutex *lock);
#define arch_mutex_cpu_relax() cpu_relax()
#endif
-#endif
+#endif /* __LINUX_MUTEX_H */
diff --git a/kernel/mutex.c b/kernel/mutex.c
index 6d647ae..4640731 100644
--- a/kernel/mutex.c
+++ b/kernel/mutex.c
@@ -25,6 +25,7 @@
#include
#include
#include
+#include
/*
* In the DEBUG case we are using the "NULL fastpath" for mutexes,
@@ -52,7 +53,7 @@ __mutex_init(struct mutex *lock, const char *name, struct
lock_class_key *key)
INIT_LIST_HEAD(>wait_list);
mutex_clear_owner(lock);
#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
- lock->spin_mlock = NULL;
+ lock->mcs_lock = NULL;
#endif
debug_mutex_init(lock, name, key);
@@ -111,54 +112,7 @@ EXPORT_SYMBOL(mutex_lock);
* more or less simultaneously, the spinners need to acquire a MCS lock
* first before spinning on the owner field.
*
- * We don't inline mspin_lock() so that perf can correctly account for the
- * time spent in this lock function.
*/
-struct mspin_node {
- struct mspin_node *next ;
- int locked; /* 1 if lock acquired */
-};
-#defineMLOCK(mutex)((struct mspin_node **)&((mutex)->spin_mlock))
-
-static noinline
-void mspin_lock(struct mspin_node **lock, struct mspin_node *node)
-{
- struct mspin_node *prev;
-
- /* Init node */
- node->locked = 0;
- node->next = NULL;
-
- prev = xchg(lock, node);
[PATCH 1/4] MCS Lock: Restructure the MCS lock defines and locking code into its own file
We will need the MCS lock code for doing optimistic spinning for rwsem.
Extracting the MCS code from mutex.c and put into its own file allow us
to reuse this code easily for rwsem.
Reviewed-by: Ingo Molnar mi...@elte.hu
Reviewed-by: Peter Zijlstra pet...@infradead.org
Signed-off-by: Tim Chen tim.c.c...@linux.intel.com
Signed-off-by: Davidlohr Bueso davidl...@hp.com
---
include/linux/mcs_spinlock.h | 64 ++
include/linux/mutex.h|5 ++-
kernel/mutex.c | 60 --
3 files changed, 74 insertions(+), 55 deletions(-)
create mode 100644 include/linux/mcs_spinlock.h
diff --git a/include/linux/mcs_spinlock.h b/include/linux/mcs_spinlock.h
new file mode 100644
index 000..b5de3b0
--- /dev/null
+++ b/include/linux/mcs_spinlock.h
@@ -0,0 +1,64 @@
+/*
+ * MCS lock defines
+ *
+ * This file contains the main data structure and API definitions of MCS lock.
+ *
+ * The MCS lock (proposed by Mellor-Crummey and Scott) is a simple spin-lock
+ * with the desirable properties of being fair, and with each cpu trying
+ * to acquire the lock spinning on a local variable.
+ * It avoids expensive cache bouncings that common test-and-set spin-lock
+ * implementations incur.
+ */
+#ifndef __LINUX_MCS_SPINLOCK_H
+#define __LINUX_MCS_SPINLOCK_H
+
+struct mcs_spinlock {
+ struct mcs_spinlock *next;
+ int locked; /* 1 if lock acquired */
+};
+
+/*
+ * We don't inline mcs_spin_lock() so that perf can correctly account for the
+ * time spent in this lock function.
+ */
+static noinline
+void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
+{
+ struct mcs_spinlock *prev;
+
+ /* Init node */
+ node-locked = 0;
+ node-next = NULL;
+
+ prev = xchg(lock, node);
+ if (likely(prev == NULL)) {
+ /* Lock acquired */
+ node-locked = 1;
+ return;
+ }
+ ACCESS_ONCE(prev-next) = node;
+ smp_wmb();
+ /* Wait until the lock holder passes the lock down */
+ while (!ACCESS_ONCE(node-locked))
+ arch_mutex_cpu_relax();
+}
+
+static void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock
*node)
+{
+ struct mcs_spinlock *next = ACCESS_ONCE(node-next);
+
+ if (likely(!next)) {
+ /*
+* Release the lock by setting it to NULL
+*/
+ if (cmpxchg(lock, node, NULL) == node)
+ return;
+ /* Wait until the next pointer is set */
+ while (!(next = ACCESS_ONCE(node-next)))
+ arch_mutex_cpu_relax();
+ }
+ ACCESS_ONCE(next-locked) = 1;
+ smp_wmb();
+}
+
+#endif /* __LINUX_MCS_SPINLOCK_H */
diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index ccd4260..e6eaeea 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -46,6 +46,7 @@
* - detects multi-task circular deadlocks and prints out all affected
* locks and tasks (and only those tasks)
*/
+struct mcs_spinlock;
struct mutex {
/* 1: unlocked, 0: locked, negative: locked, possible waiters */
atomic_tcount;
@@ -55,7 +56,7 @@ struct mutex {
struct task_struct *owner;
#endif
#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
- void*spin_mlock;/* Spinner MCS lock */
+ struct mcs_spinlock *mcs_lock; /* Spinner MCS lock */
#endif
#ifdef CONFIG_DEBUG_MUTEXES
const char *name;
@@ -179,4 +180,4 @@ extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct
mutex *lock);
#define arch_mutex_cpu_relax() cpu_relax()
#endif
-#endif
+#endif /* __LINUX_MUTEX_H */
diff --git a/kernel/mutex.c b/kernel/mutex.c
index 6d647ae..4640731 100644
--- a/kernel/mutex.c
+++ b/kernel/mutex.c
@@ -25,6 +25,7 @@
#include linux/spinlock.h
#include linux/interrupt.h
#include linux/debug_locks.h
+#include linux/mcs_spinlock.h
/*
* In the DEBUG case we are using the NULL fastpath for mutexes,
@@ -52,7 +53,7 @@ __mutex_init(struct mutex *lock, const char *name, struct
lock_class_key *key)
INIT_LIST_HEAD(lock-wait_list);
mutex_clear_owner(lock);
#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
- lock-spin_mlock = NULL;
+ lock-mcs_lock = NULL;
#endif
debug_mutex_init(lock, name, key);
@@ -111,54 +112,7 @@ EXPORT_SYMBOL(mutex_lock);
* more or less simultaneously, the spinners need to acquire a MCS lock
* first before spinning on the owner field.
*
- * We don't inline mspin_lock() so that perf can correctly account for the
- * time spent in this lock function.
*/
-struct mspin_node {
- struct mspin_node *next ;
- int locked; /* 1 if lock acquired */
-};
-#defineMLOCK(mutex)((struct mspin_node **)((mutex)-spin_mlock))
-
-static noinline
-void mspin_lock(struct mspin_node **lock, struct mspin_node *node)
-{
-
