RE: [PATCH] sched: Make nr_uninterruptible count a signed value

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Tue, 2012-05-08 at 15:14 -0700, Diwakar Tundlam wrote:
> Sorry to bug you when it is late for you..
> 
Nah, I'm the idiot still behind the screen after midnight, its just the
brain that's slightly slower and needs more hints.

> You're right, there is no real difference at all.
> Only cosmetic difference when you look at the output of
> cat /proc/sched_debug.

Not sure I see that.. the printf is still using %Ld (signed) so the
output shouldn't matter regardless of if the variable is unsigned long
or long.
> 
> But I suddenly realized maybe the increment/decrement of
> nr_interruptible is reversed.
> Maybe that's the source of the problem: decrement in activate task and
> increment in deactivate task !!

No that's right. nr_uninterruptible counts the number of tasks in
uninterruptible sleep, so deactivate_task puts a task to sleep, so we
need to increment the number of sleeping tasks, activate_task wakes a
task up so we need to decrement the number of sleeping tasks.

I think the problem you're having is that we don't match the cpu where
we inc and dec the counter, and that's fully on purpose since its rather
expensive -- it would require atomics.