[patch 08/10] lglock: introduce special lglock and brlock spin locks

[Nick Piggin]

lglock: introduce special lglock and brlock spin locks

This patch introduces "local-global" locks (lglocks). These can be used to:

- Provide fast exclusive access to per-CPU data, with exclusive access to
  another CPU's data allowed but possibly subject to contention, and to provide
  very slow exclusive access to all per-CPU data.
- Or to provide very fast and scalable read serialisation, and to provide
  very slow exclusive serialisation of data (not necessarily per-CPU data).

Brlocks are also implemented as a short-hand notation for the latter use
case.

Thanks to Paul for local/global naming convention.

Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Nick Piggin <npiggin@xxxxxxxxx>

---
 include/linux/lglock.h |  172 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 172 insertions(+)

Index: linux-2.6/include/linux/lglock.h
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6/include/linux/lglock.h	2010-08-18 04:04:29.000000000 +1000
@@ -0,0 +1,172 @@
+/*
+ * Specialised local-global spinlock. Can only be declared as global variables
+ * to avoid overhead and keep things simple (and we don't want to start using
+ * these inside dynamically allocated structures).
+ *
+ * "local/global locks" (lglocks) can be used to:
+ *
+ * - Provide fast exclusive access to per-CPU data, with exclusive access to
+ *   another CPU's data allowed but possibly subject to contention, and to
+ *   provide very slow exclusive access to all per-CPU data.
+ * - Or to provide very fast and scalable read serialisation, and to provide
+ *   very slow exclusive serialisation of data (not necessarily per-CPU data).
+ *
+ * Brlocks are also implemented as a short-hand notation for the latter use
+ * case.
+ *
+ * Copyright 2009, 2010, Nick Piggin, Novell Inc.
+ */
+#ifndef __LINUX_LGLOCK_H
+#define __LINUX_LGLOCK_H
+
+#include <linux/spinlock.h>
+#include <linux/lockdep.h>
+#include <linux/percpu.h>
+
+/* can make br locks by using local lock for read side, global lock for write */
+#define br_lock_init(name)	name##_lock_init()
+#define br_read_lock(name)	name##_local_lock()
+#define br_read_unlock(name)	name##_local_unlock()
+#define br_write_lock(name)	name##_global_lock_online()
+#define br_write_unlock(name)	name##_global_unlock_online()
+
+#define DECLARE_BRLOCK(name)	DECLARE_LGLOCK(name)
+#define DEFINE_BRLOCK(name)	DEFINE_LGLOCK(name)
+
+
+#define lg_lock_init(name)	name##_lock_init()
+#define lg_local_lock(name)	name##_local_lock()
+#define lg_local_unlock(name)	name##_local_unlock()
+#define lg_local_lock_cpu(name, cpu)	name##_local_lock_cpu(cpu)
+#define lg_local_unlock_cpu(name, cpu)	name##_local_unlock_cpu(cpu)
+#define lg_global_lock(name)	name##_global_lock()
+#define lg_global_unlock(name)	name##_global_unlock()
+#define lg_global_lock_online(name) name##_global_lock_online()
+#define lg_global_unlock_online(name) name##_global_unlock_online()
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+#define LOCKDEP_INIT_MAP lockdep_init_map
+
+#define DEFINE_LGLOCK_LOCKDEP(name)					\
+ struct lock_class_key name##_lock_key;					\
+ struct lockdep_map name##_lock_dep_map;				\
+ EXPORT_SYMBOL(name##_lock_dep_map)
+
+#else
+#define LOCKDEP_INIT_MAP(a, b, c, d)
+
+#define DEFINE_LGLOCK_LOCKDEP(name)
+#endif
+
+
+#define DECLARE_LGLOCK(name)						\
+ extern void name##_lock_init(void);					\
+ extern void name##_local_lock(void);					\
+ extern void name##_local_unlock(void);					\
+ extern void name##_local_lock_cpu(int cpu);				\
+ extern void name##_local_unlock_cpu(int cpu);				\
+ extern void name##_global_lock(void);					\
+ extern void name##_global_unlock(void);				\
+ extern void name##_global_lock_online(void);				\
+ extern void name##_global_unlock_online(void);				\
+
+#define DEFINE_LGLOCK(name)						\
+									\
+ DEFINE_PER_CPU(arch_spinlock_t, name##_lock);				\
+ DEFINE_LGLOCK_LOCKDEP(name);						\
+									\
+ void name##_lock_init(void) {						\
+	int i;								\
+	LOCKDEP_INIT_MAP(&name##_lock_dep_map, #name, &name##_lock_key, 0); \
+	for_each_possible_cpu(i) {					\
+		arch_spinlock_t *lock;					\
+		lock = &per_cpu(name##_lock, i);			\
+		*lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;	\
+	}								\
+ }									\
+ EXPORT_SYMBOL(name##_lock_init);					\
+									\
+ void name##_local_lock(void) {						\
+	arch_spinlock_t *lock;						\
+	preempt_disable();						\
+	rwlock_acquire_read(&name##_lock_dep_map, 0, 0, _THIS_IP_);	\
+	lock = &__get_cpu_var(name##_lock);				\
+	arch_spin_lock(lock);						\
+ }									\
+ EXPORT_SYMBOL(name##_local_lock);					\
+									\
+ void name##_local_unlock(void) {					\
+	arch_spinlock_t *lock;						\
+	rwlock_release(&name##_lock_dep_map, 1, _THIS_IP_);		\
+	lock = &__get_cpu_var(name##_lock);				\
+	arch_spin_unlock(lock);						\
+	preempt_enable();						\
+ }									\
+ EXPORT_SYMBOL(name##_local_unlock);					\
+									\
+ void name##_local_lock_cpu(int cpu) {					\
+	arch_spinlock_t *lock;						\
+	preempt_disable();						\
+	rwlock_acquire_read(&name##_lock_dep_map, 0, 0, _THIS_IP_);	\
+	lock = &per_cpu(name##_lock, cpu);				\
+	arch_spin_lock(lock);						\
+ }									\
+ EXPORT_SYMBOL(name##_local_lock_cpu);					\
+									\
+ void name##_local_unlock_cpu(int cpu) {				\
+	arch_spinlock_t *lock;						\
+	rwlock_release(&name##_lock_dep_map, 1, _THIS_IP_);		\
+	lock = &per_cpu(name##_lock, cpu);				\
+	arch_spin_unlock(lock);						\
+	preempt_enable();						\
+ }									\
+ EXPORT_SYMBOL(name##_local_unlock_cpu);				\
+									\
+ void name##_global_lock_online(void) {					\
+	int i;								\
+	preempt_disable();						\
+	rwlock_acquire(&name##_lock_dep_map, 0, 0, _RET_IP_);		\
+	for_each_online_cpu(i) {					\
+		arch_spinlock_t *lock;					\
+		lock = &per_cpu(name##_lock, i);			\
+		arch_spin_lock(lock);					\
+	}								\
+ }									\
+ EXPORT_SYMBOL(name##_global_lock_online);				\
+									\
+ void name##_global_unlock_online(void) {				\
+	int i;								\
+	rwlock_release(&name##_lock_dep_map, 1, _RET_IP_);		\
+	for_each_online_cpu(i) {					\
+		arch_spinlock_t *lock;					\
+		lock = &per_cpu(name##_lock, i);			\
+		arch_spin_unlock(lock);					\
+	}								\
+	preempt_enable();						\
+ }									\
+ EXPORT_SYMBOL(name##_global_unlock_online);				\
+									\
+ void name##_global_lock(void) {					\
+	int i;								\
+	preempt_disable();						\
+	rwlock_acquire(&name##_lock_dep_map, 0, 0, _RET_IP_);		\
+	for_each_online_cpu(i) {					\
+		arch_spinlock_t *lock;					\
+		lock = &per_cpu(name##_lock, i);			\
+		arch_spin_lock(lock);					\
+	}								\
+ }									\
+ EXPORT_SYMBOL(name##_global_lock);					\
+									\
+ void name##_global_unlock(void) {					\
+	int i;								\
+	rwlock_release(&name##_lock_dep_map, 1, _RET_IP_);		\
+	for_each_online_cpu(i) {					\
+		arch_spinlock_t *lock;					\
+		lock = &per_cpu(name##_lock, i);			\
+		arch_spin_unlock(lock);					\
+	}								\
+	preempt_enable();						\
+ }									\
+ EXPORT_SYMBOL(name##_global_unlock);
+#endif


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