On Wed, Mar 17, 2010 at 10:44:40AM +1100, Nick Piggin wrote:
> On Tue, Mar 16, 2010 at 01:01:09PM -0600, Andreas Dilger wrote:
> > On 2010-03-16, at 06:22, Nick Piggin wrote:
> > What makes these macros unpleasant is that it is no longer possible
> > to tag to the implementation to see what it does, since there is no
> > real declaration for these locks.
> >
> > Is it possible to change the macros to take the lock name as a
> > parameter, like normal lock/unlock functions do, and then have a
> > single declaration for br_lock_init(), br_wlock(), etc. macros?
>
> The problem is that then you can't do out of line functions, and
> things like wlock/wunlock are rather large.
>
> What I think I can do is add macros in the brlock.h file
>
> #define br_rlock(name) ##name_rlock()
>
> So the macro calls the right function and your tag should take
> you pretty close to the right place.
>
> Any better ideas how to implement this nicely would be welcome.
> It must be as light-weight as possible in the rlock path though.
It looks like this. Is it better?
--
brlock: introduce special brlocks
This patch introduces special brlocks, these can only be used as global
locks, and use some preprocessor trickery to allow us to retain a more
optimal per-cpu lock implementation. We don't bother working around
lockdep yet.
The other thing we can do in future is a really neat atomic-free
implementation like Dave M did for the old brlocks, so we might actually
be able to speed up the single-thread path for these things.
Signed-off-by: Nick Piggin <npiggin@xxxxxxx>
---
include/linux/brlock.h | 120 +++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 120 insertions(+)
Index: linux-2.6/include/linux/brlock.h
===================================================================
--- /dev/null
+++ linux-2.6/include/linux/brlock.h
@@ -0,0 +1,120 @@
+/*
+ * Specialised big-reader 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).
+ *
+ * Copyright 2009, Nick Piggin, Novell Inc.
+ */
+#ifndef __LINUX_BRLOCK_H
+#define __LINUX_BRLOCK_H
+
+#include <linux/spinlock.h>
+#include <linux/percpu.h>
+#include <asm/atomic.h>
+
+#define br_lock_init(name) name##_lock_init()
+#define br_read_lock(name) name##_read_lock()
+#define br_read_unlock(name) name##_read_unlock()
+#define br_write_lock(name) name##_write_lock()
+#define br_write_unlock(name) name##_write_unlock()
+#define atomic_dec_and_br_read_lock(atomic, name) name##_atomic_dec_and_read_lock(atomic)
+#define atomic_dec_and_br_write_lock(atomic, name) name##_atomic_dec_and_write_lock(atomic)
+
+#if defined(CONFIG_SMP) && !defined(CONFIG_LOCKDEP)
+#define DECLARE_BRLOCK(name) \
+ DECLARE_PER_CPU(spinlock_t, name##_lock); \
+ extern void name##_lock_init(void); \
+ static inline void name##_read_lock(void) { \
+ spinlock_t *lock; \
+ lock = &get_cpu_var(name##_lock); \
+ spin_lock(lock); \
+ put_cpu_var(name##_lock); \
+ } \
+ static inline void name##_read_unlock(void) { \
+ spinlock_t *lock; \
+ lock = &__get_cpu_var(name##_lock); \
+ spin_unlock(lock); \
+ } \
+ extern void name##_write_lock(void); \
+ extern void name##_write_unlock(void); \
+ static inline int name##_atomic_dec_and_read_lock(atomic_t *a) { \
+ int ret; \
+ spinlock_t *lock; \
+ lock = &get_cpu_var(name##_lock); \
+ ret = atomic_dec_and_lock(a, lock); \
+ put_cpu_var(name##_lock); \
+ return ret; \
+ } \
+ extern int name##_atomic_dec_and_write_lock__failed(atomic_t *a); \
+ static inline int name##_atomic_dec_and_write_lock(atomic_t *a) { \
+ if (atomic_add_unless(a, -1, 1)) \
+ return 0; \
+ return name##_atomic_dec_and_write_lock__failed(a); \
+ }
+
+#define DEFINE_BRLOCK(name) \
+ DEFINE_PER_CPU(spinlock_t, name##_lock); \
+ void name##_lock_init(void) { \
+ int i; \
+ for_each_possible_cpu(i) { \
+ spinlock_t *lock; \
+ lock = &per_cpu(name##_lock, i); \
+ spin_lock_init(lock); \
+ } \
+ } \
+ void name##_write_lock(void) { \
+ int i; \
+ for_each_online_cpu(i) { \
+ spinlock_t *lock; \
+ lock = &per_cpu(name##_lock, i); \
+ spin_lock(lock); \
+ } \
+ } \
+ void name##_write_unlock(void) { \
+ int i; \
+ for_each_online_cpu(i) { \
+ spinlock_t *lock; \
+ lock = &per_cpu(name##_lock, i); \
+ spin_unlock(lock); \
+ } \
+ } \
+ int name##_atomic_dec_and_write_lock__failed(atomic_t *a) { \
+ name##_write_lock(); \
+ if (!atomic_dec_and_test(a)) { \
+ name##_write_unlock(); \
+ return 0; \
+ } \
+ return 1; \
+ }
+
+#else
+
+#define DECLARE_BRLOCK(name) \
+ extern spinlock_t name##_lock; \
+ static inline void name##_lock_init(void) { \
+ spin_lock_init(&name##_lock); \
+ } \
+ static inline void name##_read_lock(void) { \
+ spin_lock(&name##_lock); \
+ } \
+ static inline void name##_read_unlock(void) { \
+ spin_unlock(&name##_lock); \
+ } \
+ static inline void name##_write_lock(void) { \
+ spin_lock(&name##_lock); \
+ } \
+ static inline void name##_write_unlock(void) { \
+ spin_unlock(&name##_lock); \
+ } \
+ static inline int name##_atomic_dec_and_read_lock(atomic_t *a) { \
+ return atomic_dec_and_lock(a, &name##_lock); \
+ } \
+ static inline int name##_atomic_dec_and_write_lock(atomic_t *a) { \
+ return atomic_dec_and_lock(a, &name##_lock); \
+ }
+
+#define DEFINE_BRLOCK(name) \
+ spinlock_t name##_lock
+#endif
+
+#endif
--
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