linux-kernel - Re: [PATCH] prepare kconfig inline optimization for all architectures

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Date:	Sun, 27 Apr 2008 20:09:57 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Adrian Bunk <bunk@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux arch <linux-arch@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH] prepare kconfig inline optimization for all architectures

On Sun, Apr 27, 2008 at 02:00:07PM -0400, Christoph Hellwig wrote:
> On Sun, Apr 27, 2008 at 08:47:14PM +0300, Adrian Bunk wrote:
> > What I want instead:
> > - we continue to force the compiler to always inline with "inline"
> > - we remove the inline's in .c files and make too big functions in 
> >   headers out-of-line
> 
> It doesn't matter whether we use inline or always_inline to force
> inlining of a function, that's just syntactical sugar.

inline => the developer hints the compiler that it may
          be a good idea to inline this function

always_inline => the developer tell gcc that for some obscure reasons
                 MUST always inline uses of this function

> What is rather
> annoying is that with the config option we'd have something marked
> inline without actually meaning it's inline.
With the config option we pass the inline hint to gcc (if enabled).
So with the config option we have the possibility to pass a _hint_ to
gcc about inlining.

Before the config option there were no difference between
static int alwyas_inline foo() {}
and
static int inline foo() {}

With the config option we now have a situation where they actually
differ as they should do (assuming gcc > 4.x).

> And what's even worse
> is that this is depending on a user-visible config option which is
> entirely stupid.
So you say that it is safe to assume all places where we really need
always_inline are annotedted such - and we do not need a simple
config option that the user can uncheck.
Fine by me - I prefer the simpler solution.

	Sam
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