Commit 982d007a authored Sep 30, 2009 by Linus Torvalds Committed by Ingo Molnar Oct 01, 2009

x86: Optimize cmpxchg64() at build-time some more



Try to avoid the 'alternates()' code when we can statically
determine that cmpxchg8b is fine. We already have that
CONFIG_x86_CMPXCHG64 (enabled by PAE support), and we could easily
also enable it for some of the CPU cases.

Note, this patch only adds CMPXCHG8B for the obvious Intel CPU's,
not for others. (There was something really messy about cmpxchg8b
and clone CPU's, so if you enable it on other CPUs later, do it
carefully.)

If we avoid that asm-alternative thing when we can assume the
instruction exists, we'll generate less support crud, and we'll
avoid the whole issue with that extra 'nop' for padding instruction
sizes etc.

LKML-Reference: <alpine.LFD.2.01.0909301743150.6996@localhost.localdomain>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 84d88d5d

arch/x86/Kconfig.cpu

+2 −1

Original line number	Diff line number	Diff line
		@@ -400,7 +400,7 @@ config X86_TSC

		config X86_CMPXCHG64
		def_bool y
		depends on X86_PAE \|\| X86_64
		depends on X86_PAE \|\| X86_64 \|\| MCORE2 \|\| MPENTIUM4 \|\| MPENTIUMM \|\| MPENTIUMIII \|\| MPENTIUMII \|\| M686 \|\| MATOM

		# this should be set for all -march=.. options where the compiler
		# generates cmov.
		@@ -412,6 +412,7 @@ config X86_MINIMUM_CPU_FAMILY
		int
		default "64" if X86_64
		default "6" if X86_32 && X86_P6_NOP
		default "5" if X86_32 && X86_CMPXCHG64
		default "4" if X86_32 && (X86_XADD \|\| X86_CMPXCHG \|\| X86_BSWAP \|\| X86_WP_WORKS_OK)
		default "3"