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authorLi Zefan <lizf@cn.fujitsu.com>2008-01-17 15:21:20 -0800
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2008-01-17 15:38:59 -0800
commit34aebfd3bdc93c0c5614f1f61e43b6ddc4be52ae (patch)
treeed8f9df6c17883382584b8df5587fd28eb39c53e /Documentation
parent545c4423335469de06af7f7c95e97c1122c1c818 (diff)
downloadop-kernel-dev-34aebfd3bdc93c0c5614f1f61e43b6ddc4be52ae.zip
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Revert "local_t Documentation update"
This reverts commit e1265205c0ee3919c3f2c750662630154c8faab2. It's a duplicate commit of commit 74beb9db77930be476b267ec8518a642f39a04bf, resulting in a duplicate section. Signed-off-by: Li Zefan <lizf@cn.fujitsu.com> Acked-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/local_ops.txt23
1 files changed, 0 insertions, 23 deletions
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- synchronization is done by the writer CPU, an outdated copy of the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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