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Date: Wed, 14 Jan 2009 20:00:08 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
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Subject: Re: [GIT PULL] adaptive spinning mutexes
Message-ID: <20090114190008.GA13203@elte.hu>
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* 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
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