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

Adrian Bunk
2008-04-27T17:22:35Z

On Sun, Apr 27, 2008 at 10:06:41AM -0700, Linus Torvalds wrote:
>
>
> On Sun, 27 Apr 2008, Adrian Bunk wrote:
> >
> > My opinion on this is still:
> > "OPTIMIZE" means "work around bugs in the kernel".
>
> No.
>
> It means that
>
> - gcc used to (long ago) always honor "inline", and we had kernel code
> that depended on that in various ways (ie required that there was no
> return etc).
>
> We've been mostly replacing the ones we know about with
> "__always_inline", but there may be some that remain. We'll find out, I
> guess.
>
> - gcc was a total and utter piece of horrible crap in the inlining
> department, doign insane things and changing their documentation to
> match the new behaviour (and some people then claimed that it was
> always documented that way).
>
> It would not inline big functions even when they statically collapsed
> to nothing, etc.
>
> As a result, we really couldn't afford to let gcc make any inlining
> decisions, because the compiler was simply *broken*.

I'm looking at it from a different angle, all code in the kernel should
follow the following rules [1]:
- no functions in .c files should be marked inline
- all functions in headers should be static inline
- all functions in headers should either be very small or collapse
to become very small after inlining

I can simply not see any usecase for a non-forced inline in the kernel,
and fixing the kernel should give a superset of the space savings of
this "inline optimization".

> Linus

cu
Adrian

[1] there might be rare exceptions

--

"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