linux-kernel - Re: 2.6.28-rc4-mmotm1110 - you gotta be kidding me...

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Date:	Tue, 11 Nov 2008 15:58:44 +1100
From:	Stephen Rothwell <sfr@...b.auug.org.au>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Valdis.Kletnieks@...edu, linux-kernel@...r.kernel.org,
	Ken Chen <kenchen@...gle.com>, Ingo Molnar <mingo@...e.hu>
Subject: Re: 2.6.28-rc4-mmotm1110 - you gotta be kidding me...

On Mon, 10 Nov 2008 19:37:13 -0800 Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Mon, 10 Nov 2008 21:55:37 -0500 Valdis.Kletnieks@...edu wrote:
> 
> > Somebody's been hitting the phunky pharmaceuticals in the last 4 days,
> > because this ball-of-joy snuck into linux-next.patch sometime between
> > -mmotm1106 and --mmotm1110.
> > 
> > Seen in a 'make silentallconfig'
> > 
> >   Single-depth WCHAN output (SCHED_NO_NO_OMIT_FRAME_POINTER) [Y/n/?] (NEW) ?
> > 
> >   Calculate simpler /proc/<PID>/wchan values. If this option
> >   is disabled then wchan values will recurse back to the
> >   caller function. This provides more accurate wchan values,
> >   at the expense of slightly more scheduling overhead.
> 
> I got lost here.
> 
> >   If in doubt, say "Y".
> > 
> > So if I say 'y', is that a request to disable it, or enable it?  And
> > what exactly do I get if I vote *against* 'more accurate wchan values'?
> > Do I get everybody having the same wchan pointing somewhere in the
> > scheduler code, because that's where __builtin_return_address() points?
> > 
> > And please - a triple negative in the Kconfig variable name?  This has
> > gotta be a winner for poor taste in variable naming...
> > 
> 
> Even if that is all sorted out, how the heck is anyone to decide
> whether or not they need this thing?
> 
> Also, if we really really are so wishy-washy indecisive that we need to
> make the function optional, it should if at all possible be made
> runtime-configurable, not compile-time.

This came from commit a87d091434ed2a34d647979ab12084139ee1fe41 ("x86,
sched: enable wchan config menu item on 64-bit").  We have had
CONFIG_SCHED_NO_NO_OMIT_FRAME_POINTER for some time on various
architectures, this commit just made it available on x86_64 (by changing
its dependency from X86_32 to X86).

-- 
Cheers,
Stephen Rothwell                    sfr@...b.auug.org.au
http://www.canb.auug.org.au/~sfr/

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