Re: [GIT PULL] adaptive spinning mutexes

Ingo Molnar
2009-01-14T19:00:08Z

* Andrew Morton <akpm@linux-foundation.org> wrote:

> On Wed, 14 Jan 2009 19:33:19 +0100 Ingo Molnar <mingo@elte.hu> wrote:
>
> > Please pull the adaptive-mutexes-for-linus git tree
>
> <fear>
>
> - It seems a major shortcoming that the feature is disabled if
> CONFIG_DEBUG_MUTEXES=y. It means that lots of people won't test it.
>
> - When people hit performance/latency oddities, it would be nice if
> they had a /proc knob with which they could disable this feature at
> runtime.
>
> This would also be useful for comparative performance testing.

Yeah. From my other mail:

> > We still have the /sys/debug/sched_features tunable under
> > CONFIG_SCHED_DEBUG=y, so should this cause any performance regressions
> > somewhere, it can be pinned down and blamed back on this change
> > easily, without bisection and without rebooting the box.

This kind of easy knob was included early on - this is how all those spin
versus no-spin numbers were done.

Ingo