Subject: Interrupt, interrupt threads, continuations, and kernel lwps
To: None <firstname.lastname@example.org>
From: Matt Thomas <email@example.com>
Date: 02/21/2007 00:08:36
After a great of pondering, I've concluded that interrupt threads are
an extremely bad idea.
I think that hard interrupts should simply invoke the handler (at the
appropriate IPL), the handler will disable the cause of the
interrupt, optionally it may use a SPIN mutex to gain control over a
shared section, do something to the device, release the mutex, or it
may just schedule a continuation to run (either via software
interrupt or via a kernel lwp workqueue, the former can't sleep/
block, the latter can).
While IPL will need to continue to exist for talking to hardware, I
think software priority levels will eventually disappear as they
currently exist. They will transition to actual real-time priorities
used by the scheduler to run kernel lwps (< SPL_SCHED) or become
mutexes (>= SPL_SCHED).