1 /*
2 * Assembly implementation of the mutex fastpath, based on atomic
3 * decrement/increment.
4 *
5 * started by Ingo Molnar:
6 *
7 * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
8 */
9 #ifndef _ASM_X86_MUTEX_64_H
10 #define _ASM_X86_MUTEX_64_H
11
12 /**
13 * __mutex_fastpath_lock - decrement and call function if negative
14 * @v: pointer of type atomic_t
15 * @fail_fn: function to call if the result is negative
16 *
17 * Atomically decrements @v and calls <fail_fn> if the result is negative.
18 */
19 #ifdef CC_HAVE_ASM_GOTO
__mutex_fastpath_lock(atomic_t * v,void (* fail_fn)(atomic_t *))20 static inline void __mutex_fastpath_lock(atomic_t *v,
21 void (*fail_fn)(atomic_t *))
22 {
23 asm_volatile_goto(LOCK_PREFIX " decl %0\n"
24 " jns %l[exit]\n"
25 : : "m" (v->counter)
26 : "memory", "cc"
27 : exit);
28 fail_fn(v);
29 exit:
30 return;
31 }
32 #else
33 #define __mutex_fastpath_lock(v, fail_fn) \
34 do { \
35 unsigned long dummy; \
36 \
37 typecheck(atomic_t *, v); \
38 typecheck_fn(void (*)(atomic_t *), fail_fn); \
39 \
40 asm volatile(LOCK_PREFIX " decl (%%rdi)\n" \
41 " jns 1f \n" \
42 " call " #fail_fn "\n" \
43 "1:" \
44 : "=D" (dummy) \
45 : "D" (v) \
46 : "rax", "rsi", "rdx", "rcx", \
47 "r8", "r9", "r10", "r11", "memory"); \
48 } while (0)
49 #endif
50
51 /**
52 * __mutex_fastpath_lock_retval - try to take the lock by moving the count
53 * from 1 to a 0 value
54 * @count: pointer of type atomic_t
55 *
56 * Change the count from 1 to a value lower than 1. This function returns 0
57 * if the fastpath succeeds, or -1 otherwise.
58 */
__mutex_fastpath_lock_retval(atomic_t * count)59 static inline int __mutex_fastpath_lock_retval(atomic_t *count)
60 {
61 if (unlikely(atomic_dec_return(count) < 0))
62 return -1;
63 else
64 return 0;
65 }
66
67 /**
68 * __mutex_fastpath_unlock - increment and call function if nonpositive
69 * @v: pointer of type atomic_t
70 * @fail_fn: function to call if the result is nonpositive
71 *
72 * Atomically increments @v and calls <fail_fn> if the result is nonpositive.
73 */
74 #ifdef CC_HAVE_ASM_GOTO
__mutex_fastpath_unlock(atomic_t * v,void (* fail_fn)(atomic_t *))75 static inline void __mutex_fastpath_unlock(atomic_t *v,
76 void (*fail_fn)(atomic_t *))
77 {
78 asm_volatile_goto(LOCK_PREFIX " incl %0\n"
79 " jg %l[exit]\n"
80 : : "m" (v->counter)
81 : "memory", "cc"
82 : exit);
83 fail_fn(v);
84 exit:
85 return;
86 }
87 #else
88 #define __mutex_fastpath_unlock(v, fail_fn) \
89 do { \
90 unsigned long dummy; \
91 \
92 typecheck(atomic_t *, v); \
93 typecheck_fn(void (*)(atomic_t *), fail_fn); \
94 \
95 asm volatile(LOCK_PREFIX " incl (%%rdi)\n" \
96 " jg 1f\n" \
97 " call " #fail_fn "\n" \
98 "1:" \
99 : "=D" (dummy) \
100 : "D" (v) \
101 : "rax", "rsi", "rdx", "rcx", \
102 "r8", "r9", "r10", "r11", "memory"); \
103 } while (0)
104 #endif
105
106 #define __mutex_slowpath_needs_to_unlock() 1
107
108 /**
109 * __mutex_fastpath_trylock - try to acquire the mutex, without waiting
110 *
111 * @count: pointer of type atomic_t
112 * @fail_fn: fallback function
113 *
114 * Change the count from 1 to 0 and return 1 (success), or return 0 (failure)
115 * if it wasn't 1 originally. [the fallback function is never used on
116 * x86_64, because all x86_64 CPUs have a CMPXCHG instruction.]
117 */
__mutex_fastpath_trylock(atomic_t * count,int (* fail_fn)(atomic_t *))118 static inline int __mutex_fastpath_trylock(atomic_t *count,
119 int (*fail_fn)(atomic_t *))
120 {
121 if (likely(atomic_cmpxchg(count, 1, 0) == 1))
122 return 1;
123 else
124 return 0;
125 }
126
127 #endif /* _ASM_X86_MUTEX_64_H */
128