title: How kernel notify a user space program an interrupt occurrs
body: <p>I'm writing a user space program and a kernel space device driver.</p>
  
  <p>Goal: Once an interrupt occurs, user space program needs to do something quickly.</p>
  
  <p>My naive method: User space program uses ioctl to call wait_event_interruptible(), kernel ISR calls wake_up_interruptible() to wake up user space program. It turns out that it takes too much time from interrupt to user space.</p>
  
  <p>Is there any better way?</p>
  
  <p>Thanks!</p>