Re: 3.4.4-rt13: btrfs + xfstests 006 = BOOM.. and a bonus rt_mutexdeadlock report for absolutely free!

From: Steven Rostedt
Date: Tue Jul 17 2012 - 00:27:56 EST

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

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

-- Steve

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