Linux driver example for Per CPU Variable

Per CPU Variables is an interesting feature available from Linux Kernel Version 2.6

When you define a Per CPU Variable, each processor in the system will have its own copy of the variable, hence no locking is required and better performance is achieved.

Header File: <linux/percpu.h>

To create a Per CPU Variable at compile time, use the macro:
DEFINE_PER_CPU(type, name);
E.g. DEFINE_PER_CPU(int, counter);

As linux kernel is preemptible, you must use
get_cpu_var macro to access the current processor's copy of a given variable
And finally call put_cpu_var macro after you have completed using it.

You can access another processor's copy of the variable with:
per_cpu(variable, int cpu_id);

Example:

Output: