On Tue, 2012-07-17 at 00:27 -0400, Steven Rostedt wrote: 

On Tue, 2012-07-17 at 06:18 +0200, Mike Galbraith wrote:

quoted

quoted

There's that too. But the issue I was talking about is with all trylock
loops. As holding an rt-mutex now disables migration, if a high priority
process preempts a task that holds the lock, and then the high prio task
starts spinning waiting for that lock to release, the lower priority
process will never get to run to release it. The cpu_chill() doesn't
help.

Hrm.  I better go make a testcase, this one definitely wants pounding
through thick skull.

Actually, I was mistaken. I forgot that we defined 'cpu_chill()' as
msleep(1) on RT, which would keep a deadlock from happening.

Whew!  There are no stars and moons on my pointy hat, just plain white
cone, so you had me worried I was missing something critical there.

It doesn't explain the performance enhancement you get :-/

No, it doesn't.  The only thing I can think of is that while folks are
timed sleeping, they aren't preempting and interleaving IO as much, but
I'm pulling that out of thin air.  Timed sleep should be a lot longer
than regular wakeup, so to my mind, there should be less interleave due
to more thumb twiddling.

-Mike