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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 1a45f11e645..4269a1105b3 100644 --- a/Documentation/local_ops.txt +++ b/Documentation/local_ops.txt @@ -68,29 +68,6 @@ typedef struct { atomic_long_t a; } local_t; variable can be read when reading some _other_ cpu's variables. -* Rules to follow when using local atomic operations - -- Variables touched by local ops must be per cpu variables. -- _Only_ the CPU owner of these variables must write to them. -- This CPU can use local ops from any context (process, irq, softirq, nmi, ...) - to update its local_t variables. -- Preemption (or interrupts) must be disabled when using local ops in - process context to make sure the process won't be migrated to a - different CPU between getting the per-cpu variable and doing the - actual local op. -- When using local ops in interrupt context, no special care must be - taken on a mainline kernel, since they will run on the local CPU with - preemption already disabled. I suggest, however, to explicitly - disable preemption anyway to make sure it will still work correctly on - -rt kernels. -- Reading the local cpu variable will provide the current copy of the - variable. -- Reads of these variables can be done from any CPU, because updates to - "long", aligned, variables are always atomic. Since no memory - synchronization is done by the writer CPU, an outdated copy of the - variable can be read when reading some _other_ cpu's variables. - - * How to use local atomic operations #include <linux/percpu.h> |