linux-kernel - Re: [2.6 patch] acpi/battery.c: make 2 functions static

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Date:	Mon, 3 Mar 2008 11:48:59 +0200
From:	Adrian Bunk <bunk@...nel.org>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Alexey Starikovskiy <aystarik@...il.com>, lenb@...nel.org,
	astarikovskiy@...e.de, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [2.6 patch] acpi/battery.c: make 2 functions static

On Mon, Mar 03, 2008 at 10:31:03AM +0100, Sam Ravnborg wrote:
> On Mon, Mar 03, 2008 at 10:17:14AM +0100, Ingo Molnar wrote:
> > 
> > * Adrian Bunk <bunk@...nel.org> wrote:
> > 
> > > On Mon, Mar 03, 2008 at 09:57:20AM +0100, Ingo Molnar wrote:
> > > > 
> > > > * Adrian Bunk <bunk@...nel.org> wrote:
> > > > 
> > > > > On Sat, Mar 01, 2008 at 09:26:41PM +0300, Alexey Starikovskiy wrote:
> > > > > > May I keep them inline?
> > > > > 
> > > > > The problem with such manual inlines is that we force gcc to always 
> > > > > inline them - and history has shown that functions grow without the 
> > > > > "inline" being removed.
> > > > 
> > > > what do you mean by "we force gcc to always inline them"?
> > > 
> > > #define inline          inline          __attribute__((always_inline))
> > > 
> > > > gcc is free to decide whether to inline or to not inline.
> > > 
> > > Not with __attribute__((always_inline)).
> > 
> > but that wasnt used in the code you patched:
> > 
> >   -inline int acpi_battery_present(struct acpi_battery *battery)
> >   +static int acpi_battery_present(struct acpi_battery *battery)
> 
> >From compiler-gcc.h:
> 
> #define inline          inline          __attribute__((always_inline))
> 
> So unless I am missing something obvious then each time we
> say inline to a function we require gcc to inline the function.

Exactly.

> It is my impression that today we only say inline if really needed
> and otherwise let gcc decide. So in almost all cases inlise should
> just be nuked?

The rule is:
- all static functions in headers should be marked inline
- no functions in .c files should be marked inline

For the latter there are a _few_ exceptions in hotpaths where doing so 
brings measurable advantages.

But generally (and especially long-term) it's best to let gcc decide 
which static functions in .c files should be inlined.

> 	Sam

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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