linux-kernel - Re: [patch] x86: phase out forced inlining

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Message-ID: <20080304080335.GA5776@uranus.ravnborg.org>
Date:	Tue, 4 Mar 2008 09:03:59 +0100
From:	Sam Ravnborg <sam@...nborg.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Adrian Bunk <bunk@...nel.org>,
	Alexey Starikovskiy <aystarik@...il.com>, lenb@...nel.org,
	astarikovskiy@...e.de, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [patch] x86: phase out forced inlining

On Mon, Mar 03, 2008 at 10:42:31PM -0800, Andrew Morton wrote:
> On Mon, 3 Mar 2008 13:13:35 +0100 Ingo Molnar <mingo@...e.hu> wrote:
> 
> > +config OPTIMIZE_INLINING
> > +	bool "Allow gcc to uninline functions marked 'inline'"
> > +	default y
> > +	help
> > +	  This option determines if the kernel forces gcc to inline the functions
> > +	  developers have marked 'inline'. Doing so takes away freedom from gcc to
> > +	  do what it thinks is best, which is desirable for the gcc 3.x series of
> > +	  compilers. The gcc 4.x series have a rewritten inlining algorithm and
> > +	  disabling this option will generate a smaller kernel there. Hopefully
> > +	  this algorithm is so good that allowing gcc4 to make the decision can
> > +	  become the default in the future, until then this option is there to
> > +	  test gcc for this.
> 
> urgh.  This will cause whatever problem
> 4507a6a59cfc6997e532cd812a8bd244181e6205 fixed five years ago to resurface
> for incautious gcc-3.x users.
> 
> I'd suggest that this
> 
> > +#ifndef CONFIG_OPTIMIZE_INLINING
> 
> become something along the lines of
> 
> > +#ifndef CONFIG_OPTIMIZE_INLINING && (__GNUC__ > 3)
> 
> It would be nice to be able to feed the gcc version into the Kconfig logic,
> really..
We can do this using a few environment options.

Somewhere in a Makefile:
export CC_MAJOR=`magic`
export CC_MINOR=`more magic`

And in a Kconfig file:

config CC_MAJOR
	string
	option env=CC_MAJOR


And then we can do:
config CC_DEFAULT_INLINE
	bool "Force inline of functions annotated inline"
	default y if CC_MAJOR = 04

Shall I try to cook up a patch for this?
[I may get access to my dev box tonight - cannot promise..]

	Sam
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