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Date:   Fri, 7 Jul 2023 13:28:05 +0200
From:   Borislav Petkov <bp@alien8.de>
To:     Dimitri John Ledkov <dimitri.ledkov@canonical.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86/cpu: Add support for modern x86-64-v* march
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References: <20230707105601.133221-1-dimitri.ledkov@canonical.com>
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On Fri, Jul 07, 2023 at 11:56:00AM +0100, Dimitri John Ledkov wrote:
> Add support for setting march to x86-64-v2, x86-64-v3, x86-64-v4 with
> tuning set to an early family of CPUs that support such instruction
> levels. By default gcc sets generic tuning for x86-64-v*, which is
> suboptimal for all brands of CPUs with such instruction set support.

Prove that it is suboptimal for the kernel. Numbers please.

And even if it shows on *some* uarch:

* we need a *single* setting for distro kernels - i.e.,
CONFIG_GENERIC_CPU and compilers do make sure that -mtune=generic does
the most optimal code generation for all uarches

* our Kconfig option set is abysmal so don't need any more if useless.

Yeah, a patch like that keeps popping up on a regular basis but no,
thanks.

-- 
Regards/Gruss,
    Boris.

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