Re: [GIT PULL] scheduler fixes

Linus Torvalds
2009-10-01T00:58:13Z

On Wed, 30 Sep 2009, Linus Torvalds wrote:
>
> Pulled. I'd also like to see something that actually fails gracefully on
> cmpxchg() of an unsupported size, though. The silent failure still annoys
> me.

Oh, and we probably should 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.

[ If I recall correctly, cmpxchg8b support detection was something that
was totally messed up in WNT, and I have this memory of TMTA _not_
claiming to support CX8 in the cpuid bits, but happily supporting the
instruction itself - because otherwise WNT would blue-screen on boot or
something silly like that.

As a result, the patch below only adds CMPXCHG8B for the obvious Intel
CPU's, not for others. There was something really messy about cmpxchg8b
and clone CPU's, but I'm not 100% sure about the details, so take this
patch with a pinch of salt, and some thinking ]

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.

Linus

---
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"