Giovanni, Ok, I divided the hrtimer by 2 (main.c, line 95), as shown below, and now it's sounds almost normal, maybe just a slightly faster. in whole fs-demo, skype gone forward for a 1 second. hrtimer_forward(&dev->timer_inq, now, ktime_set(0, SKYPOPEN_SLEEP * 1000000/2)); btw, unlocked_ioctl works too.