[PATCH] x86_64 merge: arch + asm
[opensuse:kernel.git] / include / asm-x86_64 / rwsem.h
1 /* rwsem.h: R/W semaphores implemented using XADD/CMPXCHG for x86_64+
2  *
3  * Written by David Howells (dhowells@redhat.com).
4  * Ported by Andi Kleen <ak@suse.de> to x86-64.
5  *
6  * Derived from asm-i386/semaphore.h and asm-i386/rwsem.h
7  *
8  *
9  * The MSW of the count is the negated number of active writers and waiting
10  * lockers, and the LSW is the total number of active locks
11  *
12  * The lock count is initialized to 0 (no active and no waiting lockers).
13  *
14  * When a writer subtracts WRITE_BIAS, it'll get 0xffff0001 for the case of an
15  * uncontended lock. This can be determined because XADD returns the old value.
16  * Readers increment by 1 and see a positive value when uncontended, negative
17  * if there are writers (and maybe) readers waiting (in which case it goes to
18  * sleep).
19  *
20  * The value of WAITING_BIAS supports up to 32766 waiting processes. This can
21  * be extended to 65534 by manually checking the whole MSW rather than relying
22  * on the S flag.
23  *
24  * The value of ACTIVE_BIAS supports up to 65535 active processes.
25  *
26  * This should be totally fair - if anything is waiting, a process that wants a
27  * lock will go to the back of the queue. When the currently active lock is
28  * released, if there's a writer at the front of the queue, then that and only
29  * that will be woken up; if there's a bunch of consequtive readers at the
30  * front, then they'll all be woken up, but no other readers will be.
31  */
32
33 #ifndef _X8664_RWSEM_H
34 #define _X8664_RWSEM_H
35
36 #ifndef _LINUX_RWSEM_H
37 #error please dont include asm/rwsem.h directly, use linux/rwsem.h instead
38 #endif
39
40 #ifdef __KERNEL__
41
42 #include <linux/list.h>
43 #include <linux/spinlock.h>
44
45 struct rwsem_waiter;
46
47 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
48 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
49 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
50
51 /*
52  * the semaphore definition
53  */
54 struct rw_semaphore {
55         signed long             count;
56 #define RWSEM_UNLOCKED_VALUE            0x00000000
57 #define RWSEM_ACTIVE_BIAS               0x00000001
58 #define RWSEM_ACTIVE_MASK               0x0000ffff
59 #define RWSEM_WAITING_BIAS              (-0x00010000)
60 #define RWSEM_ACTIVE_READ_BIAS          RWSEM_ACTIVE_BIAS
61 #define RWSEM_ACTIVE_WRITE_BIAS         (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
62         spinlock_t              wait_lock;
63         struct list_head        wait_list;
64 #if RWSEM_DEBUG
65         int                     debug;
66 #endif
67 };
68
69 /*
70  * initialisation
71  */
72 #if RWSEM_DEBUG
73 #define __RWSEM_DEBUG_INIT      , 0
74 #else
75 #define __RWSEM_DEBUG_INIT      /* */
76 #endif
77
78 #define __RWSEM_INITIALIZER(name) \
79 { RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, LIST_HEAD_INIT((name).wait_list) \
80         __RWSEM_DEBUG_INIT }
81
82 #define DECLARE_RWSEM(name) \
83         struct rw_semaphore name = __RWSEM_INITIALIZER(name)
84
85 static inline void init_rwsem(struct rw_semaphore *sem)
86 {
87         sem->count = RWSEM_UNLOCKED_VALUE;
88         spin_lock_init(&sem->wait_lock);
89         INIT_LIST_HEAD(&sem->wait_list);
90 #if RWSEM_DEBUG
91         sem->debug = 0;
92 #endif
93 }
94
95 /*
96  * lock for reading
97  */
98 static inline void __down_read(struct rw_semaphore *sem)
99 {
100         __asm__ __volatile__(
101                 "# beginning down_read\n\t"
102 LOCK_PREFIX     "  incl      (%%rax)\n\t" /* adds 0x00000001, returns the old value */
103                 "  js        2f\n\t" /* jump if we weren't granted the lock */
104                 "1:\n\t"
105                 ".section .text.lock,\"ax\"\n"
106                 "2:\n\t"
107                 "  call      rwsem_down_read_failed_thunk\n\t"
108                 "  jmp       1b\n"
109                 ".previous"
110                 "# ending down_read\n\t"
111                 : "+m"(sem->count)
112                 : "a"(sem)
113                 : "memory", "cc");
114 }
115
116 /*
117  * lock for writing
118  */
119 static inline void __down_write(struct rw_semaphore *sem)
120 {
121         int tmp;
122
123         tmp = RWSEM_ACTIVE_WRITE_BIAS;
124         __asm__ __volatile__(
125                 "# beginning down_write\n\t"
126 LOCK_PREFIX     "  xadd      %0,(%%rax)\n\t" /* subtract 0x0000ffff, returns the old value */
127                 "  testl     %0,%0\n\t" /* was the count 0 before? */
128                 "  jnz       2f\n\t" /* jump if we weren't granted the lock */
129                 "1:\n\t"
130                 ".section .text.lock,\"ax\"\n"
131                 "2:\n\t"
132                 "  call      rwsem_down_write_failed_thunk\n\t"
133                 "  jmp       1b\n"
134                 ".previous\n"
135                 "# ending down_write"
136                 : "=r" (tmp) 
137                 : "0"(tmp), "a"(sem)
138                 : "memory", "cc");
139 }
140
141 /*
142  * unlock after reading
143  */
144 static inline void __up_read(struct rw_semaphore *sem)
145 {
146         __s32 tmp = -RWSEM_ACTIVE_READ_BIAS;
147         __asm__ __volatile__(
148                 "# beginning __up_read\n\t"
149 LOCK_PREFIX     "  xadd      %%edx,(%%rax)\n\t" /* subtracts 1, returns the old value */
150                 "  js        2f\n\t" /* jump if the lock is being waited upon */
151                 "1:\n\t"
152                 ".section .text.lock,\"ax\"\n"
153                 "2:\n\t"
154                 "  decw      %%dx\n\t" /* do nothing if still outstanding active readers */
155                 "  jnz       1b\n\t"
156                 "  call      rwsem_wake_thunk\n\t"
157                 "  jmp       1b\n"
158                 ".previous\n"
159                 "# ending __up_read\n"
160                 : "+m"(sem->count), "+d"(tmp)
161                 : "a"(sem)
162                 : "memory", "cc");
163 }
164
165 /*
166  * unlock after writing
167  */
168 static inline void __up_write(struct rw_semaphore *sem)
169 {
170         __asm__ __volatile__(
171                 "# beginning __up_write\n\t"
172                 "  movl      %2,%%edx\n\t"
173 LOCK_PREFIX     "  xaddl     %%edx,(%%rax)\n\t" /* tries to transition 0xffff0001 -> 0x00000000 */
174                 "  jnz       2f\n\t" /* jump if the lock is being waited upon */
175                 "1:\n\t"
176                 ".section .text.lock,\"ax\"\n"
177                 "2:\n\t"
178                 "  decw      %%dx\n\t" /* did the active count reduce to 0? */
179                 "  jnz       1b\n\t" /* jump back if not */
180                 "  call      rwsem_wake_thunk\n\t"
181                 "  jmp       1b\n"
182                 ".previous\n"
183                 "# ending __up_write\n"
184                 : "+m"(sem->count)
185                 : "a"(sem), "i"(-RWSEM_ACTIVE_WRITE_BIAS)
186                 : "memory", "cc", "edx");
187 }
188
189 /*
190  * implement atomic add functionality
191  */
192 static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
193 {
194         __asm__ __volatile__(
195 LOCK_PREFIX     "addl %1,%0"
196                 :"=m"(sem->count)
197                 :"ir"(delta), "m"(sem->count));
198 }
199
200 /*
201  * implement exchange and add functionality
202  */
203 static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
204 {
205         int tmp = delta;
206
207         __asm__ __volatile__(
208 LOCK_PREFIX     "xadd %0,(%2)"
209                 : "=r"(tmp), "=m"(sem->count)
210                 : "r"(sem), "m"(sem->count), "0" (tmp)
211                 : "memory");
212
213         return tmp+delta;
214 }
215
216 #endif /* __KERNEL__ */
217 #endif /* _I386_RWSEM_H */