Re: Interrupt handlers in NetBSD 5.0

[Andrew Doran <ad%netbsd.org@localhost>]

On Mon, Jun 08, 2009 at 09:24:26PM +0100, Mindaugas Rasiukevicius wrote:

> Hans Petter Selasky <hselasky%c2i.net@localhost> wrote:
> > I have a quick question:
> > 
> > How are interrupt handlers implemented in NetBSD 5.0?
> > 
> 
> It looks like you are interested in software interrupts. They are described
> in softint(9) manual page.
> 
> > Are the interrupt handlers deferred to an interrupt thread so that locking 
> > a kernel mutex from within the interrupt handler is allowed?
> 
> Yes, mutex(9) could be used from soft interrupt handlers.

To elaborate on what Mindaugas said:

- Interrrupt handlers look somewhat like a traditional Unix system, but
  there are fewer priority levels.

- Software interrupts work like hardware interrupts for the most part, but
  they have partial thread context and so can sleep on locks. This works a
  bit like Solaris, if you are familiar with it.

- There's no implicit deferral of work to threads like FreeBSD does with
  hardware interrupts. If you need thread context for locking then work must
  be passed to another level: to a softint, to a workqueue, to the eventual
  consumer, or to a kthread using a custom mechanism.

Also have a look at the spl(9) page, it gives some more details on interrupt
structure and what you can do at the various priority levels.