diff options
Diffstat (limited to 'arch/x86/include/asm/barrier.h')
-rw-r--r-- | arch/x86/include/asm/barrier.h | 59 |
1 files changed, 3 insertions, 56 deletions
diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h index 0f4460b5636d..5238000285c1 100644 --- a/arch/x86/include/asm/barrier.h +++ b/arch/x86/include/asm/barrier.h | |||
@@ -24,60 +24,6 @@ | |||
24 | #define wmb() asm volatile("sfence" ::: "memory") | 24 | #define wmb() asm volatile("sfence" ::: "memory") |
25 | #endif | 25 | #endif |
26 | 26 | ||
27 | /** | ||
28 | * read_barrier_depends - Flush all pending reads that subsequents reads | ||
29 | * depend on. | ||
30 | * | ||
31 | * No data-dependent reads from memory-like regions are ever reordered | ||
32 | * over this barrier. All reads preceding this primitive are guaranteed | ||
33 | * to access memory (but not necessarily other CPUs' caches) before any | ||
34 | * reads following this primitive that depend on the data return by | ||
35 | * any of the preceding reads. This primitive is much lighter weight than | ||
36 | * rmb() on most CPUs, and is never heavier weight than is | ||
37 | * rmb(). | ||
38 | * | ||
39 | * These ordering constraints are respected by both the local CPU | ||
40 | * and the compiler. | ||
41 | * | ||
42 | * Ordering is not guaranteed by anything other than these primitives, | ||
43 | * not even by data dependencies. See the documentation for | ||
44 | * memory_barrier() for examples and URLs to more information. | ||
45 | * | ||
46 | * For example, the following code would force ordering (the initial | ||
47 | * value of "a" is zero, "b" is one, and "p" is "&a"): | ||
48 | * | ||
49 | * <programlisting> | ||
50 | * CPU 0 CPU 1 | ||
51 | * | ||
52 | * b = 2; | ||
53 | * memory_barrier(); | ||
54 | * p = &b; q = p; | ||
55 | * read_barrier_depends(); | ||
56 | * d = *q; | ||
57 | * </programlisting> | ||
58 | * | ||
59 | * because the read of "*q" depends on the read of "p" and these | ||
60 | * two reads are separated by a read_barrier_depends(). However, | ||
61 | * the following code, with the same initial values for "a" and "b": | ||
62 | * | ||
63 | * <programlisting> | ||
64 | * CPU 0 CPU 1 | ||
65 | * | ||
66 | * a = 2; | ||
67 | * memory_barrier(); | ||
68 | * b = 3; y = b; | ||
69 | * read_barrier_depends(); | ||
70 | * x = a; | ||
71 | * </programlisting> | ||
72 | * | ||
73 | * does not enforce ordering, since there is no data dependency between | ||
74 | * the read of "a" and the read of "b". Therefore, on some CPUs, such | ||
75 | * as Alpha, "y" could be set to 3 and "x" to 0. Use rmb() | ||
76 | * in cases like this where there are no data dependencies. | ||
77 | **/ | ||
78 | |||
79 | #define read_barrier_depends() do { } while (0) | ||
80 | |||
81 | #ifdef CONFIG_SMP | 27 | #ifdef CONFIG_SMP |
82 | #define smp_mb() mb() | 28 | #define smp_mb() mb() |
83 | #ifdef CONFIG_X86_PPRO_FENCE | 29 | #ifdef CONFIG_X86_PPRO_FENCE |
@@ -86,16 +32,17 @@ | |||
86 | # define smp_rmb() barrier() | 32 | # define smp_rmb() barrier() |
87 | #endif | 33 | #endif |
88 | #define smp_wmb() barrier() | 34 | #define smp_wmb() barrier() |
89 | #define smp_read_barrier_depends() read_barrier_depends() | ||
90 | #define set_mb(var, value) do { (void)xchg(&var, value); } while (0) | 35 | #define set_mb(var, value) do { (void)xchg(&var, value); } while (0) |
91 | #else /* !SMP */ | 36 | #else /* !SMP */ |
92 | #define smp_mb() barrier() | 37 | #define smp_mb() barrier() |
93 | #define smp_rmb() barrier() | 38 | #define smp_rmb() barrier() |
94 | #define smp_wmb() barrier() | 39 | #define smp_wmb() barrier() |
95 | #define smp_read_barrier_depends() do { } while (0) | ||
96 | #define set_mb(var, value) do { var = value; barrier(); } while (0) | 40 | #define set_mb(var, value) do { var = value; barrier(); } while (0) |
97 | #endif /* SMP */ | 41 | #endif /* SMP */ |
98 | 42 | ||
43 | #define read_barrier_depends() do { } while (0) | ||
44 | #define smp_read_barrier_depends() do { } while (0) | ||
45 | |||
99 | #if defined(CONFIG_X86_PPRO_FENCE) | 46 | #if defined(CONFIG_X86_PPRO_FENCE) |
100 | 47 | ||
101 | /* | 48 | /* |