Linux内核获取当前CPU id

CPU id是​​percpu变量​​​，调用​​smp_processor_id()​​可以取出。内核里对它的注释如下：

smp_processor_id() is safe if it's used in a preemption-off critical section, or in a thread that is bound to the current CPU.

所以除非是在绑定在CPU上的线程中使用，否则必须要先关抢占。内核已经封装了带关抢占的API：

#define get_cpu()   ({ preempt_disable(); smp_processor_id(); })
#define put_cpu()   preempt_enable()

典型用法：

int cpuid = get_cpu();
// Do something
put_cpu()