ia64/linux-2.6.18-xen.hg

view include/asm-generic/mutex-dec.h @ 782:9ab1c319531f

merge with linux-2.6.18-xen.hg
author Isaku Yamahata <yamahata@valinux.co.jp>
date Wed Jan 28 13:07:23 2009 +0900 (2009-01-28)
parents 831230e53067
children
line source
1 /*
2 * asm-generic/mutex-dec.h
3 *
4 * Generic implementation of the mutex fastpath, based on atomic
5 * decrement/increment.
6 */
7 #ifndef _ASM_GENERIC_MUTEX_DEC_H
8 #define _ASM_GENERIC_MUTEX_DEC_H
10 /**
11 * __mutex_fastpath_lock - try to take the lock by moving the count
12 * from 1 to a 0 value
13 * @count: pointer of type atomic_t
14 * @fail_fn: function to call if the original value was not 1
15 *
16 * Change the count from 1 to a value lower than 1, and call <fail_fn> if
17 * it wasn't 1 originally. This function MUST leave the value lower than
18 * 1 even when the "1" assertion wasn't true.
19 */
20 static inline void
21 __mutex_fastpath_lock(atomic_t *count, fastcall void (*fail_fn)(atomic_t *))
22 {
23 if (unlikely(atomic_dec_return(count) < 0))
24 fail_fn(count);
25 else
26 smp_mb();
27 }
29 /**
30 * __mutex_fastpath_lock_retval - try to take the lock by moving the count
31 * from 1 to a 0 value
32 * @count: pointer of type atomic_t
33 * @fail_fn: function to call if the original value was not 1
34 *
35 * Change the count from 1 to a value lower than 1, and call <fail_fn> if
36 * it wasn't 1 originally. This function returns 0 if the fastpath succeeds,
37 * or anything the slow path function returns.
38 */
39 static inline int
40 __mutex_fastpath_lock_retval(atomic_t *count, fastcall int (*fail_fn)(atomic_t *))
41 {
42 if (unlikely(atomic_dec_return(count) < 0))
43 return fail_fn(count);
44 else {
45 smp_mb();
46 return 0;
47 }
48 }
50 /**
51 * __mutex_fastpath_unlock - try to promote the count from 0 to 1
52 * @count: pointer of type atomic_t
53 * @fail_fn: function to call if the original value was not 0
54 *
55 * Try to promote the count from 0 to 1. If it wasn't 0, call <fail_fn>.
56 * In the failure case, this function is allowed to either set the value to
57 * 1, or to set it to a value lower than 1.
58 *
59 * If the implementation sets it to a value of lower than 1, then the
60 * __mutex_slowpath_needs_to_unlock() macro needs to return 1, it needs
61 * to return 0 otherwise.
62 */
63 static inline void
64 __mutex_fastpath_unlock(atomic_t *count, fastcall void (*fail_fn)(atomic_t *))
65 {
66 smp_mb();
67 if (unlikely(atomic_inc_return(count) <= 0))
68 fail_fn(count);
69 }
71 #define __mutex_slowpath_needs_to_unlock() 1
73 /**
74 * __mutex_fastpath_trylock - try to acquire the mutex, without waiting
75 *
76 * @count: pointer of type atomic_t
77 * @fail_fn: fallback function
78 *
79 * Change the count from 1 to a value lower than 1, and return 0 (failure)
80 * if it wasn't 1 originally, or return 1 (success) otherwise. This function
81 * MUST leave the value lower than 1 even when the "1" assertion wasn't true.
82 * Additionally, if the value was < 0 originally, this function must not leave
83 * it to 0 on failure.
84 *
85 * If the architecture has no effective trylock variant, it should call the
86 * <fail_fn> spinlock-based trylock variant unconditionally.
87 */
88 static inline int
89 __mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
90 {
91 /*
92 * We have two variants here. The cmpxchg based one is the best one
93 * because it never induce a false contention state. It is included
94 * here because architectures using the inc/dec algorithms over the
95 * xchg ones are much more likely to support cmpxchg natively.
96 *
97 * If not we fall back to the spinlock based variant - that is
98 * just as efficient (and simpler) as a 'destructive' probing of
99 * the mutex state would be.
100 */
101 #ifdef __HAVE_ARCH_CMPXCHG
102 if (likely(atomic_cmpxchg(count, 1, 0) == 1)) {
103 smp_mb();
104 return 1;
105 }
106 return 0;
107 #else
108 return fail_fn(count);
109 #endif
110 }
112 #endif