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SubjectSpecific support for Intel Atom architecture
Date
Hi,

as some of you already might know, work is going on to make GCC fully support
Intel Atom architecture specifics, i.e. make -mtune=atom generate code
optimized for in-order architectures like Intel Atom [1].

I therefore started to make up a small patch which adds Intel Atom as a new
processor family which can be selected upon configuration. It's nothing
special and also requires a patched GCC. I'd just like to get some feedback on
it, i.e. is X86_L1_CACHE_SHIFT=6 ok for Atom CPUs (I was not able to find any
information on Atom's cacheline size)? Any chance to include this patch once
the Atom patch went into GCC mainline (probably in GCC 4.5)? Any other
objections?

Please Cc me, I'm not on the list.

Regards,

Tobias

[1] http://gcc.gnu.org/viewcvs/branches/ix86/atom/


From 6aa86b4431619d38849d469c70904afe1e5a8ca0 Mon Sep 17 00:00:00 2001
From: Tobias Doerffel <tobias.doerffel@gmail.com>
Date: Thu, 30 Apr 2009 12:36:46 +0200
Subject: [PATCH] x86: add specific support for Intel Atom architecture

This adds another option when selecting CPU family so the kernel can
be optimized for Intel Atom CPUs. This patch requires a GCC with a
patch applied which adds specific Intel Atom support.
---
arch/x86/Kconfig.cpu | 19 ++++++++++++++-----
arch/x86/Makefile_32.cpu | 1 +
arch/x86/include/asm/module.h | 2 ++
3 files changed, 17 insertions(+), 5 deletions(-)
diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu
index 8130334..8e565b7 100644
--- a/arch/x86/Kconfig.cpu
+++ b/arch/x86/Kconfig.cpu
@@ -262,6 +262,15 @@ config MCORE2
family in /proc/cpuinfo. Newer ones have 6 and older ones 15
(not a typo)

+config MATOM
+ bool "Intel Atom"
+ depends on X86_32
+ ---help---
+
+ Select this for Intel Atom platform. Intel Atom CPUs have an in-order
+ pipelining architecture and thus can benefit from in-order optimized
+ code (requires Intel Atom patch in GCC).
+
config GENERIC_CPU
bool "Generic-x86-64"
depends on X86_64
@@ -310,7 +319,7 @@ config X86_L1_CACHE_SHIFT
default "7" if MPENTIUM4 || MPSC
default "4" if X86_ELAN || M486 || M386 || MGEODEGX1
default "5" if MWINCHIP3D || MWINCHIPC6 || MCRUSOE || MEFFICEON || MCYRIXIII || MK6 || MPENTIUMIII || MPENTIUMII || M686 || M586MMX || M586TSC || M586 || MVIAC3_2 || MGEODE_LX
- default "6" if MK7 || MK8 || MPENTIUMM || MCORE2 || MVIAC7 || X86_GENERIC || GENERIC_CPU
+ default "6" if MK7 || MK8 || MPENTIUMM || MCORE2 || MATOM || MVIAC7 || X86_GENERIC || GENERIC_CPU

config X86_XADD
def_bool y
@@ -355,11 +364,11 @@ config X86_ALIGNMENT_16

config X86_INTEL_USERCOPY
def_bool y
- depends on MPENTIUM4 || MPENTIUMM || MPENTIUMIII || MPENTIUMII || M586MMX || X86_GENERIC || MK8 || MK7 || MEFFICEON || MCORE2
+ depends on MPENTIUM4 || MPENTIUMM || MPENTIUMIII || MPENTIUMII || M586MMX || X86_GENERIC || MK8 || MK7 || MEFFICEON || MCORE2 || MATOM

config X86_USE_PPRO_CHECKSUM
def_bool y
- depends on MWINCHIP3D || MWINCHIPC6 || MCYRIXIII || MK7 || MK6 || MPENTIUM4 || MPENTIUMM || MPENTIUMIII || MPENTIUMII || M686 || MK8 || MVIAC3_2 || MEFFICEON || MGEODE_LX || MCORE2
+ depends on MWINCHIP3D || MWINCHIPC6 || MCYRIXIII || MK7 || MK6 || MPENTIUM4 || MPENTIUMM || MPENTIUMIII || MPENTIUMII || M686 || MK8 || MVIAC3_2 || MEFFICEON || MGEODE_LX || MCORE2 || MATOM

config X86_USE_3DNOW
def_bool y
@@ -387,7 +396,7 @@ config X86_P6_NOP

config X86_TSC
def_bool y
- depends on ((MWINCHIP3D || MCRUSOE || MEFFICEON || MCYRIXIII || MK7 || MK6 || MPENTIUM4 || MPENTIUMM || MPENTIUMIII || MPENTIUMII || M686 || M586MMX || M586TSC || MK8 || MVIAC3_2 || MVIAC7 || MGEODEGX1 || MGEODE_LX || MCORE2) && !X86_NUMAQ) || X86_64
+ depends on ((MWINCHIP3D || MCRUSOE || MEFFICEON || MCYRIXIII || MK7 || MK6 || MPENTIUM4 || MPENTIUMM || MPENTIUMIII || MPENTIUMII || M686 || M586MMX || M586TSC || MK8 || MVIAC3_2 || MVIAC7 || MGEODEGX1 || MGEODE_LX || MCORE2 || MATOM) && !X86_NUMAQ) || X86_64

config X86_CMPXCHG64
def_bool y
@@ -397,7 +406,7 @@ config X86_CMPXCHG64
# generates cmov.
config X86_CMOV
def_bool y
- depends on (MK8 || MK7 || MCORE2 || MPENTIUM4 || MPENTIUMM || MPENTIUMIII || MPENTIUMII || M686 || MVIAC3_2 || MVIAC7 || MCRUSOE || MEFFICEON || X86_64)
+ depends on (MK8 || MK7 || MCORE2 || MPENTIUM4 || MPENTIUMM || MPENTIUMIII || MPENTIUMII || M686 || MVIAC3_2 || MVIAC7 || MCRUSOE || MEFFICEON || X86_64 || MATOM)

config X86_MINIMUM_CPU_FAMILY
int
diff --git a/arch/x86/Makefile_32.cpu b/arch/x86/Makefile_32.cpu
index 80177ec..07a11b0 100644
--- a/arch/x86/Makefile_32.cpu
+++ b/arch/x86/Makefile_32.cpu
@@ -33,6 +33,7 @@ cflags-$(CONFIG_MCYRIXIII) += $(call cc-option,-march=c3,-march=i486) $(align)-f
cflags-$(CONFIG_MVIAC3_2) += $(call cc-option,-march=c3-2,-march=i686)
cflags-$(CONFIG_MVIAC7) += -march=i686
cflags-$(CONFIG_MCORE2) += -march=i686 $(call tune,core2)
+cflags-$(CONFIG_MATOM) += -march=atom $(call tune,atom)

# AMD Elan support
cflags-$(CONFIG_X86_ELAN) += -march=i486
diff --git a/arch/x86/include/asm/module.h b/arch/x86/include/asm/module.h
index 47d6274..e959c4a 100644
--- a/arch/x86/include/asm/module.h
+++ b/arch/x86/include/asm/module.h
@@ -28,6 +28,8 @@ struct mod_arch_specific {};
#define MODULE_PROC_FAMILY "586MMX "
#elif defined CONFIG_MCORE2
#define MODULE_PROC_FAMILY "CORE2 "
+#elif defined CONFIG_MATOM
+#define MODULE_PROC_FAMILY "ATOM "
#elif defined CONFIG_M686
#define MODULE_PROC_FAMILY "686 "
#elif defined CONFIG_MPENTIUMII
--
1.6.2.4
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