Re: [PATCH 03/13] jump label v9: x86 support

[Andi Kleen]

On Thu, Jun 10, 2010 at 02:14:40PM +0200, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> 
> > On Wed, 2010-06-09 at 17:39 -0400, Jason Baron wrote:
> > > +       select HAVE_ARCH_JUMP_LABEL if !CC_OPTIMIZE_FOR_SIZE
> > 
> > That deserves a comment somewhere, it basically makes OPTIMIZE_FOR_SIZE 
> > useless...
> 
> Hm, we need more than a comment for that - distros enable CC_OPTIMIZE_FOR_SIZE 
> all the time, for the massive kernel image (and hotpath cache footprint) 
> savings. Is this fixable?

Actually the big distros (RHEL, SLES) disable it all the time now. It costs you 
in some benchmarks. The code generated by -Os is often terrible.

Nearly everytime I investigate some bad asm code being generated by gcc
it goes away when that flag is disabled.

A much better to get smaller kernel images is to do more __cold
annotations for slow paths. Newer gcc will then simply only do -Os for these 
functions.

It's already done for __init.

-Andi
-- 
ak@xxxxxxxxxxxxxxx -- Speaking for myself only.
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