How kernel notify a user space program an interrupt occurrs

7
votes

I'm writing a user space program and a kernel space device driver.

Goal: Once an interrupt occurs, user space program needs to do something quickly.

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.

Is there any better way?

Thanks!

1
linuxinterrupt
Have you used nice to increase the program's priority? – Ben Voigt
I'm using uClinux. There is no "nice" command. However, I did try to use sched_get_priority_max();sched_setscheduler(); in my user space program but it doesn't really help. :( – user1747565
busybox has nice, renice, and chpst. If any of those applets are enabled, you can use them to run your user-space program with a differently priority. Is it running as root (only the superuser can raise priority)? – Ben Voigt
I would use in kernel driver a dedicated char device for the purpose of signaling the application (which should poll(2) that device). – Basile Starynkevitch
Thanks Ben, I just found the "nice" option in busybox. I'll try it later! – user1747565

1 Answers

3
votes

There is a similar question asked here:

Notify gpio interrupt to user space from a kernel module

Please check above question. However, i can provide my approach which i suggested there as well.

You can send a signal to user space thread from kernel API, which can help u run non-blocking:

send_sig(int sig, struct task_struct *p, int priv);

You need to be aware of pid of user thread in Kernel. You can over come this by writing pid of user process via /proc and then kernel reading the pid. With this arrangement, when there is an interrupt, kernel can send signal to user thread. In case your process restarts or gets killed, you will have to update the pid via proc. Just for status notification you can use this method; however if you like to transfer data along with status than Netlink or char driver mechanism is good way.