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authorPaul Mackerras <paulus@samba.org>2008-01-24 10:07:21 +1100
committerPaul Mackerras <paulus@samba.org>2008-01-24 10:07:21 +1100
commit9156ad48338e0306e508ead5c0d9986050744475 (patch)
tree37f3a90e38190052ecf3cdf9171dfdddd37b56fd /Documentation/local_ops.txt
parentfa28237cfcc5827553044cbd6ee52e33692b0faa (diff)
parent8f7b3d156d348b6766833cd4e272d0d19b501e64 (diff)
downloadop-kernel-dev-9156ad48338e0306e508ead5c0d9986050744475.zip
op-kernel-dev-9156ad48338e0306e508ead5c0d9986050744475.tar.gz
Merge branch 'linux-2.6'
Diffstat (limited to 'Documentation/local_ops.txt')
-rw-r--r--Documentation/local_ops.txt23
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diff --git a/Documentation/local_ops.txt b/Documentation/local_ops.txt
index 1a45f11..4269a11 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- synchronization is done by the writer CPU, an outdated copy of the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>
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