Messages in this thread | | | Date | Thu, 10 Jun 2010 15:26:16 +0200 | From | Andi Kleen <> | Subject | Re: [PATCH 03/13] jump label v9: x86 support |
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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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