| Ingo Molnar | b8aa036 | 2006-01-09 15:59:18 -0800 | [diff] [blame] | 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_MUTEX_H |
| 10 | #define _ASM_MUTEX_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 | #define __mutex_fastpath_lock(v, fail_fn) \ |
| 20 | do { \ |
| 21 | unsigned long dummy; \ |
| 22 | \ |
| 23 | typecheck(atomic_t *, v); \ |
| 24 | typecheck_fn(fastcall void (*)(atomic_t *), fail_fn); \ |
| 25 | \ |
| 26 | __asm__ __volatile__( \ |
| 27 | LOCK " decl (%%rdi) \n" \ |
| 28 | " js 2f \n" \ |
| 29 | "1: \n" \ |
| 30 | \ |
| 31 | LOCK_SECTION_START("") \ |
| 32 | "2: call "#fail_fn" \n" \ |
| 33 | " jmp 1b \n" \ |
| 34 | LOCK_SECTION_END \ |
| 35 | \ |
| 36 | :"=D" (dummy) \ |
| 37 | : "D" (v) \ |
| 38 | : "rax", "rsi", "rdx", "rcx", \ |
| 39 | "r8", "r9", "r10", "r11", "memory"); \ |
| 40 | } while (0) |
| 41 | |
| 42 | /** |
| 43 | * __mutex_fastpath_lock_retval - try to take the lock by moving the count |
| 44 | * from 1 to a 0 value |
| 45 | * @count: pointer of type atomic_t |
| 46 | * @fail_fn: function to call if the original value was not 1 |
| 47 | * |
| 48 | * Change the count from 1 to a value lower than 1, and call <fail_fn> if |
| 49 | * it wasn't 1 originally. This function returns 0 if the fastpath succeeds, |
| 50 | * or anything the slow path function returns |
| 51 | */ |
| 52 | static inline int |
| 53 | __mutex_fastpath_lock_retval(atomic_t *count, |
| 54 | int fastcall (*fail_fn)(atomic_t *)) |
| 55 | { |
| 56 | if (unlikely(atomic_dec_return(count) < 0)) |
| 57 | return fail_fn(count); |
| 58 | else |
| 59 | return 0; |
| 60 | } |
| 61 | |
| 62 | /** |
| 63 | * __mutex_fastpath_unlock - increment and call function if nonpositive |
| 64 | * @v: pointer of type atomic_t |
| 65 | * @fail_fn: function to call if the result is nonpositive |
| 66 | * |
| 67 | * Atomically increments @v and calls <fail_fn> if the result is nonpositive. |
| 68 | */ |
| 69 | #define __mutex_fastpath_unlock(v, fail_fn) \ |
| 70 | do { \ |
| 71 | unsigned long dummy; \ |
| 72 | \ |
| 73 | typecheck(atomic_t *, v); \ |
| 74 | typecheck_fn(fastcall void (*)(atomic_t *), fail_fn); \ |
| 75 | \ |
| 76 | __asm__ __volatile__( \ |
| 77 | LOCK " incl (%%rdi) \n" \ |
| 78 | " jle 2f \n" \ |
| 79 | "1: \n" \ |
| 80 | \ |
| 81 | LOCK_SECTION_START("") \ |
| 82 | "2: call "#fail_fn" \n" \ |
| 83 | " jmp 1b \n" \ |
| 84 | LOCK_SECTION_END \ |
| 85 | \ |
| 86 | :"=D" (dummy) \ |
| 87 | : "D" (v) \ |
| 88 | : "rax", "rsi", "rdx", "rcx", \ |
| 89 | "r8", "r9", "r10", "r11", "memory"); \ |
| 90 | } while (0) |
| 91 | |
| 92 | #define __mutex_slowpath_needs_to_unlock() 1 |
| 93 | |
| 94 | /** |
| 95 | * __mutex_fastpath_trylock - try to acquire the mutex, without waiting |
| 96 | * |
| 97 | * @count: pointer of type atomic_t |
| 98 | * @fail_fn: fallback function |
| 99 | * |
| 100 | * Change the count from 1 to 0 and return 1 (success), or return 0 (failure) |
| 101 | * if it wasn't 1 originally. [the fallback function is never used on |
| 102 | * x86_64, because all x86_64 CPUs have a CMPXCHG instruction.] |
| 103 | */ |
| 104 | static inline int |
| 105 | __mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *)) |
| 106 | { |
| 107 | if (likely(atomic_cmpxchg(count, 1, 0)) == 1) |
| 108 | return 1; |
| 109 | else |
| 110 | return 0; |
| 111 | } |
| 112 | |
| 113 | #endif |