percpu: update local_ops.txt to reflect this_cpu operations
Update the documentation to reflect changes due to the availability of
this_cpu operations.
Signed-off-by: Christoph Lameter <cl@linux.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/local_ops.txt b/Documentation/local_ops.txt
index 300da4b..407576a 100644
--- a/Documentation/local_ops.txt
+++ b/Documentation/local_ops.txt
@@ -8,6 +8,11 @@
properly. It also stresses on the precautions that must be taken when reading
those local variables across CPUs when the order of memory writes matters.
+Note that local_t based operations are not recommended for general kernel use.
+Please use the this_cpu operations instead unless there is really a special purpose.
+Most uses of local_t in the kernel have been replaced by this_cpu operations.
+this_cpu operations combine the relocation with the local_t like semantics in
+a single instruction and yield more compact and faster executing code.
* Purpose of local atomic operations
@@ -87,10 +92,10 @@
local_inc(&get_cpu_var(counters));
put_cpu_var(counters);
-If you are already in a preemption-safe context, you can directly use
-__get_cpu_var() instead.
+If you are already in a preemption-safe context, you can use
+this_cpu_ptr() instead.
- local_inc(&__get_cpu_var(counters));
+ local_inc(this_cpu_ptr(&counters));
@@ -134,7 +139,7 @@
{
/* Increment the counter from a non preemptible context */
printk("Increment on cpu %d\n", smp_processor_id());
- local_inc(&__get_cpu_var(counters));
+ local_inc(this_cpu_ptr(&counters));
/* This is what incrementing the variable would look like within a
* preemptible context (it disables preemption) :