全局时钟中断的用处是什么？

今天看深入理解内核，里面介绍了全局时钟中断（依赖PIC）和cpu本地时钟中断（依赖apic）
内核的定时器处理和软中断的处理以及时间的更新都是依赖于cpu本地的时钟中断的，那全局的pic时钟中断有何用呢？

这本书的中英文版本，都不是这么说的。你恐怕看岔了。
Chapter 6.2
In a multiprocessor system, all general activities (such as handling of software timers)
are triggered by the interrupts raised by the global timer,
while CPU-specific activities (such as monitoring the execution time of the currently running process)
are triggered by the interrupts raised by the local APIC timer.