linux-kernel - Re: 2.6.23-rc1: BUG_ON in kmap_atomic

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Message-ID: <20070724194046.GD6019@stusta.de>
Date:	Tue, 24 Jul 2007 21:40:46 +0200
From:	Adrian Bunk <bunk@...sta.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: 2.6.23-rc1: BUG_ON in kmap_atomic_prot()

On Tue, Jul 24, 2007 at 12:15:48PM -0700, Linus Torvalds wrote:
> 
> 
> On Tue, 24 Jul 2007, Andrew Morton wrote:
> > 
> > fwiw, -fno-inline-functions-called-once (who knew?) takes i386 allnoconfig
> > vmlinux .text from 928360 up to 955362 bytes (27k larger).
> > 
> > A surprisingly large increase - I wonder if it did something dumb.  It
> > appears to still correctly inline those things which we've manually marked
> > inline.  hm.
> 
> I think inlining small enough functions is worth it, and the thing is, the 
> kernel is actually pretty damn good at having lots of small functions. 
> It's one of the few things I really care about from a coding style 
> standpoint.
> 
> So I'm not surprised that "-fno-inline-functions-called-once" makes things 
> larger, because I think it's generally a good idea to inline things that 
> are just called once. But it does make things harder to debug, and the 
> performance advantages become increasingly small for bigger functions.
> 
> And that's a balancing act. Do we care about performance? Yes.

When using CONFIG_CC_OPTIMIZE_FOR_SIZE=y we even actively tell gcc that 
we only care about size and do not care about performance...

> But do we 
> care so much that it's worth inlining something like buffered_rmqueue()? 
>...

Where is the problem with having buffered_rmqueue() inlined?

> 		Linus

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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