X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=Documentation%2Flocal_ops.txt;h=f4f8b1c6c8ba45ba6ec351aa92c40e798024983c;hb=e2858ce3ed519500e3b9af1c16c25250ff16cd5c;hp=1a45f11e645e978f445ba7396f0c5411a1695e06;hpb=95b00786f3b8fa99f53931361beeb4c10504ad87;p=pandora-kernel.git diff --git a/Documentation/local_ops.txt b/Documentation/local_ops.txt index 1a45f11e645e..f4f8b1c6c8ba 100644 --- a/Documentation/local_ops.txt +++ b/Documentation/local_ops.txt @@ -36,7 +36,7 @@ It can be done by slightly modifying the standard atomic operations : only 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 @@ -45,29 +45,6 @@ long fails. The definition looks like : 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 Since no memory - synchronization is done by the writer CPU, an outdated copy of the - variable can be read when reading some _other_ cpu's variables.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.