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C/C++ Source or Header  |  2008-12-24  |  2.9 KB  |  101 lines
  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. #define __mutex_fastpath_lock(v, fail_fn)            \
  20. do {                                \
  21.     unsigned long dummy;                    \
  22.                                 \
  23.     typecheck(atomic_t *, v);                \
  24.     typecheck_fn(void (*)(atomic_t *), fail_fn);        \
  25.                                 \
  26.     asm volatile(LOCK_PREFIX "   decl (%%rdi)\n"        \
  27.              "   jns 1f        \n"            \
  28.              "   call " #fail_fn "\n"            \
  29.              "1:"                    \
  30.              : "=D" (dummy)                \
  31.              : "D" (v)                    \
  32.              : "rax", "rsi", "rdx", "rcx",        \
  33.                "r8", "r9", "r10", "r11", "memory");    \
  34. } while (0)
  35.  
  36. /**
  37.  *  __mutex_fastpath_lock_retval - try to take the lock by moving the count
  38.  *                                 from 1 to a 0 value
  39.  *  @count: pointer of type atomic_t
  40.  *  @fail_fn: function to call if the original value was not 1
  41.  *
  42.  * Change the count from 1 to a value lower than 1, and call <fail_fn> if
  43.  * it wasn't 1 originally. This function returns 0 if the fastpath succeeds,
  44.  * or anything the slow path function returns
  45.  */
  46. static inline int __mutex_fastpath_lock_retval(atomic_t *count,
  47.                            int (*fail_fn)(atomic_t *))
  48. {
  49.     if (unlikely(atomic_dec_return(count) < 0))
  50.         return fail_fn(count);
  51.     else
  52.         return 0;
  53. }
  54.  
  55. /**
  56.  * __mutex_fastpath_unlock - increment and call function if nonpositive
  57.  * @v: pointer of type atomic_t
  58.  * @fail_fn: function to call if the result is nonpositive
  59.  *
  60.  * Atomically increments @v and calls <fail_fn> if the result is nonpositive.
  61.  */
  62. #define __mutex_fastpath_unlock(v, fail_fn)            \
  63. do {                                \
  64.     unsigned long dummy;                    \
  65.                                 \
  66.     typecheck(atomic_t *, v);                \
  67.     typecheck_fn(void (*)(atomic_t *), fail_fn);        \
  68.                                 \
  69.     asm volatile(LOCK_PREFIX "   incl (%%rdi)\n"        \
  70.              "   jg 1f\n"                \
  71.              "   call " #fail_fn "\n"            \
  72.              "1:"                    \
  73.              : "=D" (dummy)                \
  74.              : "D" (v)                    \
  75.              : "rax", "rsi", "rdx", "rcx",        \
  76.                "r8", "r9", "r10", "r11", "memory");    \
  77. } while (0)
  78.  
  79. #define __mutex_slowpath_needs_to_unlock()    1
  80.  
  81. /**
  82.  * __mutex_fastpath_trylock - try to acquire the mutex, without waiting
  83.  *
  84.  *  @count: pointer of type atomic_t
  85.  *  @fail_fn: fallback function
  86.  *
  87.  * Change the count from 1 to 0 and return 1 (success), or return 0 (failure)
  88.  * if it wasn't 1 originally. [the fallback function is never used on
  89.  * x86_64, because all x86_64 CPUs have a CMPXCHG instruction.]
  90.  */
  91. static inline int __mutex_fastpath_trylock(atomic_t *count,
  92.                        int (*fail_fn)(atomic_t *))
  93. {
  94.     if (likely(atomic_cmpxchg(count, 1, 0) == 1))
  95.         return 1;
  96.     else
  97.         return 0;
  98. }
  99.  
  100. #endif /* _ASM_X86_MUTEX_64_H */
  101.