Mastering Linux Kernel Development

CPU local timer

PIT is a global timer, and interrupts raised by it that can be handled by any CPU in an SMP system. In some cases, having such a common timer is beneficial, whereas in other cases, a per-CPU timer is more desirable. In an SMP system, keeping process time and monitoring allotted time slices to a process in each CPU would be much easier and efficient with a local timer.

Local APIC in recent x86 microprocessors embeds such a CPU local timer. A CPU local timer can issue interrupts either once or periodically. It uses a 32-bit timer and can issue interrupts at a very low frequency (this wider counter allows more ticks to occur before an interrupt is raised). The APIC timer works with the bus clock signal. The APIC timer is quite ...