their UP variant must be kept. It typically means removing LOCK prefix (on
i386 and x86_64) and any SMP sychronization barrier. If the architecture does
not have a different behavior between SMP and UP, including asm-generic/local.h
-in your archtecture's local.h is sufficient.
+in your architecture's local.h is sufficient.
The local_t type is defined as an opaque signed long by embedding an
atomic_long_t inside a structure. This is made so a cast from this type to a
typedef struct { atomic_long_t a; } local_t;
-* 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- synchronization is done by the writer CPU, an outdated copy of the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.
-
-
* Rules to follow when using local atomic operations
- Variables touched by local ops must be per cpu variables.
git.openpandora.org / pandora-kernel.git / blobdiff