How does the kernel update current process's time statistics?

On a uniprocessor, the global timer interrupt handler calls
update_process_times() to update current process time statistics.

call chain:

   timer_interrupt() (arch/i386/kernel/time.c)
     do_timer_interrupt (arch/i386/timer.c)
       do_timer_interrupt_hook (include/asm-i386/mach-*/do_timer.h)
         #ifndef CONFIG_SMP
         update_process_times (kernel/timer.c)
           scheduler_tick (kernel/sched.c)

On a multiprocessor, global timer interrupt is no longer used to update
process time statistics.  Instead, we use local APIC timer.

   smp_acpi_timer_interrupt (arch/i386/kernel/apic.c)
     smp_local_timer_interrupt (arch/i386/kernel/apic.c)
       #ifdef CONFIG_SMP
       update_process_times (kernel/timer.c)
         scheduler_tick (kernel/sched.c)