With -mmovbe enabled (implicit with -march=atom), this allows the compiler to use the movbe instruction. This doesn't have a significant effect on code size (unlike on PowerPC), because the movbe instruction actually takes as many bytes to encode as a simple mov and a bswap. But for Atom in particular I believe it should give a performance win over the mov+bswap alternative. That was kind of why movbe was invented in the first place, after all... I've done basic functionality testing with IPv6 and Legacy IP, but no performance testing. The EFI firmware on my test box unfortunately no longer starts up. Signed-off-by: David Woodhouse <David.Woodhouse@xxxxxxxxx> Acked-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx> --- arch/x86/Kconfig | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 97f8c5a..2ab0f0c 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -115,6 +115,7 @@ config X86 select MODULES_USE_ELF_REL if X86_32 select MODULES_USE_ELF_RELA if X86_64 select CLONE_BACKWARDS if X86_32 + select ARCH_USE_BUILTIN_BSWAP config INSTRUCTION_DECODER def_bool y -- 1.8.0.1 -- dwmw2
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