jump label v9: x86 support
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From: Ingo Molnar on 10 Jun 2010 08:20 * Peter Zijlstra <peterz(a)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? Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Peter Zijlstra on 10 Jun 2010 08:20 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... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Peter Zijlstra on 10 Jun 2010 08:20 On Wed, 2010-06-09 at 17:39 -0400, Jason Baron wrote: > +#define JUMP_LABEL(tag, label, cond) \ > + do { \ > + extern const char __jlstrtab_##tag[]; \ > + asm goto("1:" \ > + JUMP_LABEL_NOP \ > + ".pushsection __jump_table, \"a\" \n\t"\ > + _ASM_PTR "1b, %l[" #label "], %c0 \n\t" \ > + ".popsection \n\t" \ > + : : "i" (__jlstrtab_##tag) : : label);\ > + } while (0) Would it make sense to have that macro at least evaluate cond in some way? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Peter Zijlstra on 10 Jun 2010 08:40 On Wed, 2010-06-09 at 17:39 -0400, Jason Baron wrote: > add x86 support for jump label. I'm keeping this patch separate so its clear to > arch maintainers what was required for x86 support this new feature. hopefully, > it wouldn't be too painful for other arches. Well patch 10 really rather spoils that, doesn't it? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Andi Kleen on 10 Jun 2010 09:30
On Thu, Jun 10, 2010 at 02:14:40PM +0200, Ingo Molnar wrote: > > * Peter Zijlstra <peterz(a)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(a)linux.intel.com -- Speaking for myself only. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |