[tip:x86/urgent] x86: Optimize cmpxchg64() at build-time some more

tip-bot for Linus Torvalds
2009-10-01T06:41:31Z

Commit-ID: 982d007a6eec4a0abb404d2355eeec2c041c61ea
Gitweb: http://git.kernel.org/tip/982d007a6eec4a0abb404d2355eeec2c041c61ea
Author: Linus Torvalds <torvalds@linux-foundation.org>
AuthorDate: Wed, 30 Sep 2009 17:57:27 -0700
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Thu, 1 Oct 2009 08:01:08 +0200

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>

---
arch/x86/Kconfig.cpu | 3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu
index 527519b..f2824fb 100644
--- a/arch/x86/Kconfig.cpu
+++ b/arch/x86/Kconfig.cpu
@@ -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"