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

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Date:	Wed, 14 Jan 2009 21:51:22 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
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


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

> > > Do people enable CONFIG_SCHED_DEBUG?
> > 
> > If they suspect performance problems and want to analyze them?
> 
> The vast majority of users do not and usually cannot compile their own 
> kernels.

... which they derive from distro kernels or some old .config they always 
used, via 'make oldconfig'. You are arguing against well-established facts 
here.

If you dont believe my word for it, here's an analysis of all kernel 
configs posted to lkml in the past 8 months:

   $ grep ^CONFIG_SCHED_DEBUG linux-kernel | wc -l
   424

   $ grep 'CONFIG_SCHED_DEBUG is not' linux-kernel | wc -l
   109

i.e. CONFIG_SCHED_DEBUG=y is set in 80% of the configs. A large majority 
of testers has it enabled and /sys/debug/sched_features was always a good 
mechanism that we used for runtime toggles.

> > Note that CONFIG_SCHED_DEBUG=y is also the default.
> 
> akpm:/usr/src/25> echo $ARCH
> x86_64
> akpm:/usr/src/25> make defconfig
> *** Default configuration is based on 'x86_64_defconfig'

x86 defconfig is used too, but it's a pretty rare usage.

Under default i mean the customary meaning of default config: it's the 
default if you come via 'make oldconfig' or if you derive your config from 
a distro config:

| config SCHED_DEBUG
|        bool "Collect scheduler debugging info"
|        depends on DEBUG_KERNEL && PROC_FS
|        default y

	Ingo
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