Re: [PATCH -v8][RFC] mutex: implement adaptive spinning

Peter Zijlstra
2009-01-12T17:16:21Z

On Mon, 2009-01-12 at 08:20 -0800, Linus Torvalds wrote:
>
> On Mon, 12 Jan 2009, Linus Torvalds wrote:
> >
> > You made it back into the locked version.
>
> Btw, even if you probably had some reason for this, one thing to note is
> that I think Chris' performance testing showed that the version using a
> lock was inferior to his local btrfs hack, while the unlocked version
> actually beat his hack.
>
> Maybe I misunderstood his numbers, though. But if I followed that sub-part
> of the test right, it really means that the locked version is pointless -
> it will never be able to replace peoples local hacks for this same thing,
> because it just doesn't give the performance people are looking for.
>
> Since the whole (and _only_) point of this thing is to perform well,
> that's a big deal.

Like said in reply to Chris' email, I just wanted to see if fairness was
worth the effort, because the pure unlocked spin showed significant
unfairness (and I know some people really care about some level of
fairness).

Initial testing with the simple test-mutex thing didn't show too bad
numbers.