Re: [PATCH -v11][RFC] mutex: implement adaptive spinning

[Peter Zijlstra <peterz@infradead.org>]

On Thu, 2009-01-15 at 01:46 +0100, Nick Piggin wrote:

> Hmm, well this is rather a slow path, I would say. I'd prefer not to
> modify schedule in this way (if we just get scheduled back on after
> being switched away, the subsequent call to schedule is going to be
> cache hot and not do too much work).
> 
> preempt_enable_noresched maybe if you really care, would close up the
> window even more. But is it really worthwhile? We'd want to see numbers
> (when in doubt, keep it  simpler).

I initially did the preempt_enable_no_resched() thing and that showed
some improvement for PREEMPT=y kernels (lost the numbers though).

When I redid all the patches I tried closing that last hole by doing
that __schedule() thing, never realizing that schedule() would then get
extra overhead,.. d'0h.

I agree that that isn't worth it. I shall revert to
preempt_enable_no_resched() and try to get some new numbers.