Wait queue question

Ian Abbott abbotti at mev.co.uk
Thu Feb 15 05:04:07 EST 2001

Ralph Blach wrote:

> If I have a wait queue thats I am using to wake up a device
> driver read
> from an interrupt service routine.
> If I get three interrupt and three wake_up_interrables, will I need to
> execute three sleep_ons to get the wait queue back to the
> null state, or
> is it just back after the first sleep_on?

They do not work like semaphores. wake_up and wake_up_interruptible have
an immediate effect on processes waiting on the specified queue, but
don't modify a counter or anything like that. This also means you can't
sleep on an event that has already happened, like you could with a

Also, you probably want to use interruptible_sleep_on rather than
sleep_on, unless you've already considered this.

These are general Linux driver writing questions, rather than embedded
Linux PPC questions. You may be better off addressing these sorts of
questions to a different list or newsgroup. Also, you may wish to
consider investing in Alessandro Rubini's "Linux Device Drivers",
published by O'Reilly. It's starting to get a little out-of-date in
places but is still a good introduction to writing device drivers for

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