什么是Linux本地计时器中断？

The local APIC present in recent 80×86 microprocessors (see the
section “Interrupts and Exceptions” in Chapter 4) provides yet another
time-measuring device: the CPU local timer.

The CPU local timer is a device similar to the Programmable Interval
Timer just described that can issue one-shot or periodic interrupts.
There are,however,a few differences:

• The APIC’s timer counter is 32 bits long,while the PIT’s timer counter is 16 bits long; therefore,the local timer can be programmed
  to issue interrupts at very low frequencies (the counter stores the
  number of ticks that must elapse before the interrupt is issued).
• The local APIC timer sends an interrupt only to its processor,while the PIT raises a global interrupt,which may be handled by any
  CPU in the system.
• The APIC’s timer is based on the bus clock signal (or the APIC bus signal,in older machines). It can be programmed in such a way to decrease the timer counter every 1,2,4,8,16,32,64,or 128 bus clock signals. Conversely,the PIT,which makes use of its own clock signals,can be programmed in a more flexible way.