Re: [PATCH -v9][RFC] mutex: implement adaptive spinning

[Ingo Molnar <mingo@elte.hu>]

* Peter Zijlstra <peterz@infradead.org> wrote:

> > Now you're forcing the slow-path on unlock. Maybe it was intentional, 
> > maybe it wasn't. Did you perhaps mean
> > 
> > 	if (atomic_cmpxchg(&lock->count, 1, 0) == 1) {
> > 
> > here? I thought we agreed it was safe, if only because it should be 
> > equivalent to just having done "mutex_trylock()" instead of a "real" 
> > lock sequence.
> 
> Yes, that was an 'accident' from -v8, yes we did think the cmpxchg was 
> good, however I did get some spurious lockups on -v7, and I only noticed 
> the thing after I'd done most of the testing, so I decided to let it be 
> for now.
> 
> Let me put the cmpxchg back in and see if this is all still good (only 
> 3*2*2 configs to test :-).

i saw sporadic lockups with -v7 too, so if you send a -v10 with Linus's 
sequence for the unlock it takes about an hour of testing to check whether 
it still occurs.

	Ingo