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: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Frank Mayhar <fmayhar@xxxxxxxxxx>,
Cc: John Stultz <johnstul@xxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Signed-off-by: Nick Piggin <npiggin@xxxxxxx>
---
include/linux/lglock.h | 172 +++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 172 insertions(+)
Index: linux-2.6/include/linux/lglock.h
===================================================================
--- /dev/null
+++ linux-2.6/include/linux/lglock.h
@@ -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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