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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>
This commit is contained in:
Linus Torvalds 2009-09-30 17:57:27 -07:00 committed by Ingo Molnar
parent 84d88d5d4e
commit 982d007a6e
1 changed files with 2 additions and 1 deletions
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3
arch/x86/Kconfig.cpu
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@ -400,7 +400,7 @@ config X86_TSC
config X86_CMPXCHG64 config X86_CMPXCHG64
def_bool y 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 # this should be set for all -march=.. options where the compiler
# generates cmov. # generates cmov.
@ -412,6 +412,7 @@ config X86_MINIMUM_CPU_FAMILY
int int
default "64" if X86_64 default "64" if X86_64
default "6" if X86_32 && X86_P6_NOP 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 "4" if X86_32 && (X86_XADD || X86_CMPXCHG || X86_BSWAP || X86_WP_WORKS_OK)
default "3" default "3"