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SubjectRe: [PATCH 03/13] jump label v9: x86 support
On Thu, Jun 10, 2010 at 02:14:40PM +0200, Ingo Molnar wrote:
>
> * Peter Zijlstra <peterz@infradead.org> 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@linux.intel.com -- Speaking for myself only.


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