linux-kernel - Re: [GIT PULL] adaptive spinning mutexes

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Date:	Wed, 14 Jan 2009 11:36:38 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	torvalds@...ux-foundation.org, a.p.zijlstra@...llo.nl,
	paulmck@...ux.vnet.ibm.com, ghaskins@...ell.com, matthew@....cx,
	andi@...stfloor.org, chris.mason@...cle.com,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-btrfs@...r.kernel.org, tglx@...utronix.de, npiggin@...e.de,
	pmorreale@...ell.com, SDietrich@...ell.com,
	dmitry.adamushko@...il.com, hannes@...xchg.org
Subject: Re: [GIT PULL] adaptive spinning mutexes

On Wed, 14 Jan 2009 20:00:08 +0100
Ingo Molnar <mingo@...e.hu> wrote:

> 
> * Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > On Wed, 14 Jan 2009 19:33:19 +0100 Ingo Molnar <mingo@...e.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.

Do people enable CONFIG_SCHED_DEBUG?

CONFIG_DEBUG_MUTEXES=n, CONFIG_SCHED_DEBUG=y is getting to be a pretty
small subset?

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