linux-kernel - Re: [GIT PULL] scheduler fixes

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Date:	Thu, 01 Oct 2009 07:30:38 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...radead.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <johnstul@...ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [GIT PULL] scheduler fixes

Linus Torvalds a écrit :
> 
> On Wed, 30 Sep 2009, Linus Torvalds wrote:
> 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.
> 

Agreed.

Please find following patch to conditionaly compile cmpxchg8b_emu.o and
EXPORT_SYMBOL(cmpxchg8b_emu).

This patch doesnt depend on yours.

Thanks

[PATCH] x86: Dont generate cmpxchg8b_emu if CONFIG_X86_CMPXCHG64=y

cmpxchg8b_emu helper wont be used if CONFIG_X86_CMPXCHG64=y

Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
---
 arch/x86/kernel/i386_ksyms_32.c |    2 ++
 arch/x86/lib/Makefile           |    6 ++++--
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/i386_ksyms_32.c b/arch/x86/kernel/i386_ksyms_32.c
index 1736c5a..9c3bd4a 100644
--- a/arch/x86/kernel/i386_ksyms_32.c
+++ b/arch/x86/kernel/i386_ksyms_32.c
@@ -15,8 +15,10 @@ EXPORT_SYMBOL(mcount);
  * the export, but dont use it from C code, it is used
  * by assembly code and is not using C calling convention!
  */
+#ifndef CONFIG_X86_CMPXCHG64
 extern void cmpxchg8b_emu(void);
 EXPORT_SYMBOL(cmpxchg8b_emu);
+#endif
 
 /* Networking helper routines. */
 EXPORT_SYMBOL(csum_partial_copy_generic);
diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index 3e549b8..c309b82 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -15,8 +15,10 @@ ifeq ($(CONFIG_X86_32),y)
         obj-y += atomic64_32.o
         lib-y += checksum_32.o
         lib-y += strstr_32.o
-        lib-y += semaphore_32.o string_32.o cmpxchg8b_emu.o
-
+        lib-y += semaphore_32.o string_32.o
+ifeq ($(CONFIG_X86_CMPXCHG64),n)
+        lib-y += cmpxchg8b_emu.o
+endif
         lib-$(CONFIG_X86_USE_3DNOW) += mmx_32.o
 else
         obj-y += io_64.o iomap_copy_64.o
--
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