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Diffstat (limited to 'Documentation/local_ops.txt')
-rw-r--r-- | Documentation/local_ops.txt | 23 |
1 files changed, 0 insertions, 23 deletions
diff --git a/Documentation/local_ops.txt b/Documentation/local_ops.txt index 1a45f11e645e..4269a1105b37 100644 --- a/Documentation/local_ops.txt +++ b/Documentation/local_ops.txt | |||
@@ -68,29 +68,6 @@ typedef struct { atomic_long_t a; } local_t; | |||
68 | variable can be read when reading some _other_ cpu's variables. | 68 | variable can be read when reading some _other_ cpu's variables. |
69 | 69 | ||
70 | 70 | ||
71 | * Rules to follow when using local atomic operations | ||
72 | |||
73 | - Variables touched by local ops must be per cpu variables. | ||
74 | - _Only_ the CPU owner of these variables must write to them. | ||
75 | - This CPU can use local ops from any context (process, irq, softirq, nmi, ...) | ||
76 | to update its local_t variables. | ||
77 | - Preemption (or interrupts) must be disabled when using local ops in | ||
78 | process context to make sure the process won't be migrated to a | ||
79 | different CPU between getting the per-cpu variable and doing the | ||
80 | actual local op. | ||
81 | - When using local ops in interrupt context, no special care must be | ||
82 | taken on a mainline kernel, since they will run on the local CPU with | ||
83 | preemption already disabled. I suggest, however, to explicitly | ||
84 | disable preemption anyway to make sure it will still work correctly on | ||
85 | -rt kernels. | ||
86 | - Reading the local cpu variable will provide the current copy of the | ||
87 | variable. | ||
88 | - Reads of these variables can be done from any CPU, because updates to | ||
89 | "long", aligned, variables are always atomic. Since no memory | ||
90 | synchronization is done by the writer CPU, an outdated copy of the | ||
91 | variable can be read when reading some _other_ cpu's variables. | ||
92 | |||
93 | |||
94 | * How to use local atomic operations | 71 | * How to use local atomic operations |
95 | 72 | ||
96 | #include <linux/percpu.h> | 73 | #include <linux/percpu.h> |