Problem about timer-interrupt

[echo579]

I add a loop in software/timer-interrupt/timer-interrupt.c to check intr_count update, and find nothing output. Is the timer-interrupt must be trigged by function metal_cpu_set_mtimecmp(cpu, 0);
Following is my code about the loop in timer-interrupt.c

    printf("before return %d\n", intr_count);
    int last = intr_count;
    while(1)
    {
        if(intr_count != last){
            printf("tmr updated %d\n", intr_count);
            last = intr_count;
        }
    }

I'm curious why timer-interrupt doesn't trigger automated.