Re: [PATCH 2/2] x86, Makefile: Add new generic x86-64 settings v2/v3/v4

[Nick Desaulniers]

On Tue, Aug 17, 2021 at 7:24 AM torvic9 via Clang Built Linux
<clang-built-linux@xxxxxxxxxxxxxxxx> wrote:
>
> Add new generic x86-64 CPU tunings introduced with recent versions of
> gcc and clang, as documented in x86-64-psABI [1].
>
> This is taken straight from graysky's CPU optimization patch with minor
> modifications [2].
>
> [1] https://gitlab.com/x86-psABIs/x86-64-ABI/-/commit/77566eb03bc6a326811cb7e9a6b9396884b67c7c
> [2] https://github.com/graysky2/kernel_compiler_patch
>
> Signed-off-by: Tor Vic <torvic9@xxxxxxxxxxx>
> ---
>  arch/x86/Kconfig.cpu  | 26 +++++++++++++++++++++++++-
>  arch/x86/Makefile.cpu |  6 ++++++
>  2 files changed, 31 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu
> index 814fe0d349b0..a2c872aa5a0b 100644
> --- a/arch/x86/Kconfig.cpu
> +++ b/arch/x86/Kconfig.cpu
> @@ -294,6 +294,30 @@ config GENERIC_CPU
>           Generic x86-64 CPU.
>           Run equally well on all x86-64 CPUs.
>
> +config GENERIC_CPU_V2
> +       bool "Generic-x86-64-v2"
> +       depends on ( CC_IS_GCC && GCC_VERSION > 110000 ) || ( CC_IS_CLANG && CLANG_VERSION >= 120000 )

Can we stick with either > or >=, but at least be consistent? Also,
there's unnecessary whitespace inside the parens that could be
removed.

> +       depends on X86_64
> +       help
> +         Generic x86-64 CPU.
> +         Run equally well on all x86-64 CPUs with min support of x86-64-v2.
> +
> +config GENERIC_CPU_V3
> +       bool "Generic-x86-64-v3"
> +       depends on ( CC_IS_GCC && GCC_VERSION > 110000 ) || ( CC_IS_CLANG && CLANG_VERSION >= 120000 )
> +       depends on X86_64
> +       help
> +         Generic x86-64-v3 CPU with v3 instructions.
> +         Run equally well on all x86-64 CPUs with min support of x86-64-v3.
> +
> +config GENERIC_CPU_V4
> +       bool "Generic-x86-64-v4"
> +       depends on ( CC_IS_GCC && GCC_VERSION > 110000 ) || ( CC_IS_CLANG && CLANG_VERSION >= 120000 )
> +       depends on X86_64
> +       help
> +         Generic x86-64 CPU with v4 instructions.
> +         Run equally well on all x86-64 CPUs with min support of x86-64-v4.
> +
>  endchoice
>
>  config X86_GENERIC
> @@ -318,7 +342,7 @@ config X86_INTERNODE_CACHE_SHIFT
>  config X86_L1_CACHE_SHIFT
>         int
>         default "7" if MPENTIUM4 || MPSC
> -       default "6" if MK7 || MK8 || MPENTIUMM || MCORE2 || MATOM || MVIAC7 || X86_GENERIC || GENERIC_CPU
> +       default "6" if MK7 || MK8 || MPENTIUMM || MCORE2 || MATOM || MVIAC7 || X86_GENERIC || GENERIC_CPU || GENERIC_CPU_V2 || GENERIC_CPU_V3 || GENERIC_CPU_V4
>         default "4" if MELAN || M486SX || M486 || MGEODEGX1
>         default "5" if MWINCHIP3D || MWINCHIPC6 || MCRUSOE || MEFFICEON || MCYRIXIII || MK6 || MPENTIUMIII || MPENTIUMII || M686 || M586MMX || M586TSC || M586 || MVIAC3_2 || MGEODE_LX
>
> diff --git a/arch/x86/Makefile.cpu b/arch/x86/Makefile.cpu
> index fb407ae94d90..f190feefe964 100644
> --- a/arch/x86/Makefile.cpu
> +++ b/arch/x86/Makefile.cpu
> @@ -10,3 +10,9 @@ cflags-$(CONFIG_MCORE2) += \
>  cflags-$(CONFIG_MATOM) += $(call cc-option,-march=atom) \
>         $(call cc-option,-mtune=atom,$(call cc-option,-mtune=generic))
>  cflags-$(CONFIG_GENERIC_CPU) += $(call cc-option,-mtune=generic)
> +
> +# New generic x86-64 CPU options.
> +# Don't call the compiler, we have Kconfig compiler checks for these.

You'd be surprised how quickly using time-relative words like "New"
bitrot. My copy of "Modern C++" already doesn't feel very "modern" for
example.  I'd just drop the comment block here; we don't need a
comment every time we skip cc-option checks.  Thanks for the patches!

> +cflags-$(CONFIG_GENERIC_CPU_V2) += -march=x86-64-v2
> +cflags-$(CONFIG_GENERIC_CPU_V3) += -march=x86-64-v3
> +cflags-$(CONFIG_GENERIC_CPU_V4) += -march=x86-64-v4
> --
-- 
Thanks,
~Nick Desaulniers