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Date:   Tue, 17 Aug 2021 20:36:35 +0200
From:   Borislav Petkov <bp@alien8.de>
To:     torvic9@mailbox.org
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>,
        "clang-built-linux@googlegroups.com" 
        <clang-built-linux@googlegroups.com>,
        "graysky@archlinux.us" <graysky@archlinux.us>
Subject: Re: [PATCH 2/2] x86, Makefile: Add new generic x86-64 settings
 v2/v3/v4
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 <796036867.117557.1629210288168@office.mailbox.org>
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On Tue, Aug 17, 2021 at 04:24:48PM +0200, torvic9@mailbox.org 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@mailbox.org>
> ---
>  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 )
> +	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.

Every once in a while, patches like that pop up without any real numbers
advocating for the additional and perhaps unnecessary complexity.

If those -march switches don't bring any measureable improvements - and
I highly doubt they do - you shouldn't waste time with submitting them.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette