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 <[e-mail]>
Cc: Tejun Heo <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

Documentation/local_ops.txt

···
 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+Most uses of local_t in the kernel have been replaced by this_cpu operations.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
···
 	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));
 
 
 
···
 {
 	/* 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) :