From 34aebfd3bdc93c0c5614f1f61e43b6ddc4be52ae Mon Sep 17 00:00:00 2001 From: Li Zefan Date: Thu, 17 Jan 2008 15:21:20 -0800 Subject: [PATCH] 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 Acked-by: Mathieu Desnoyers Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/local_ops.txt | 23 ----------------------- 1 file changed, 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 Since no memory - synchronization is done by the writer CPU, an outdated copy of the - variable can be read when reading some _other_ cpu's variables.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 -- 2.11.4.GIT