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

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Date:	Sun, 27 Apr 2008 21:41:06 +0300
From:	Adrian Bunk <bunk@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Sam Ravnborg <sam@...nborg.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 11:11:27AM -0700, Linus Torvalds wrote:
> 
> 
> On Sun, 27 Apr 2008, 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
> 
> Sure, I can agree with that as a mostly good goal, but you're still 
> ignoring the fact that nobody should really expect the compiler to always 
> do a good job at deciding high-level issues.
> 
> For example, what's wrong with having "inline" on functions in .c files if 
> the author thinks they are small enough? He's likely right. Considering 
> past behaviour, he's quite often more right than the compiler.
>...

Ingo's commit in your tree just broke this assumption.

And he justified breaking it with a 2.3% size decrease.

And after
- grep'ing for "inline" through drivers/
- remembering how driver authors use likely/unlikely
- remembering the practically non-existing quality criteria you set
  for new drivers [1]
"He's likely right." is likely not right for the average driver author.

You might be smarter than gcc, but most kernel developers (including me) 
are not.

> 		Linus

cu
Adrian

[1] you said you really wanted this driver merged in this state in 2.6.25:

      grep -C4 volatile drivers/infiniband/hw/nes/nes_nic.c


-- 

       "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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