Re: Specific support for Intel Atom architecture

From: Ingo Molnar
Date: Thu Apr 30 2009 - 11:41:24 EST


* Tobias Doerffel <tobias.doerffel@xxxxxxxxx> wrote:

> 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@xxxxxxxxx>
> 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

Makes sense. One question would be X86_L1_CACHE_SHIFT - you set it
to 2^6 == 64 - that's correct i think, most Atoms come with 64 byte
L2 cache AFAIK.

I've Cc:-ed Intel folks - is this assumption about 64 bytes correct?

Ingo
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