Linux 调度器之抢占

//include/linux/preempt.h 
#define preempt_disable() \ 
do { \ 
    preempt_count_inc(); \ 
    barrier(); \ 
} while (0) 
 
#define preempt_count_inc() preempt_count_add(1) //include/linux/preempt.h 
 
#define preempt_count_add(val)    __preempt_count_add(val) //include/linux/preempt.h 
 
static inline void __preempt_count_add(int val) //arch/arm64/include/asm/preempt.h 
{ 
    /* 使用的是 current->thread_info.preempt.count */ 
    u32 pc = READ_ONCE(current_thread_info()->preempt.count); 
    pc += val; 
    WRITE_ONCE(current_thread_info()->preempt.count, pc); 
}

#define preempt_enable() \ 
do { \ 
    barrier(); \ 
    if (unlikely(preempt_count_dec_and_test())) \ 
        __preempt_schedule(); \ 
} while (0)