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-rw-r--r--arch/x86/include/asm/barrier.h59
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/*