linux-kernel - Re: [PATCH] x86: add more x86-64 micro-architecture levels

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Message-ID: <20240915124944.GAZubX6LAcjQjN-yEb@fat_crate.local>
Date: Sun, 15 Sep 2024 14:49:44 +0200
From: Borislav Petkov <bp@...en8.de>
To: John <therealgraysky@...ton.me>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, Unknown <x86@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86: add more x86-64 micro-architecture levels

On Sun, Sep 15, 2024 at 11:05:52AM +0000, John wrote:
> GCC 11.1 and Clang 12.0[1] allow for the following new generic
> 64-bit levels: x86-64-v2, x86-64-v3, and x86-64-v4.  This commit
> adds them as options accessible under:
>  Processor type and features  --->
>   Processor family --->
> 
> Users of glibc 2.33 and above can see which level is supported
> by running: /lib/ld-linux-x86-64.so.2 --help | grep supported
> 
> or: /lib64/ld-linux-x86-64.so.2 --help | grep supported
> 
> ACKNOWLEDGMENTS
> This patch builds on the seminal work by Jeroen.[2]
> 
> REFERENCES
> 1.  https://gitlab.com/x86-psABIs/x86-64-ABI/-/commit/77566eb03bc6a326811cb7e9
> 2.  http://www.linuxforge.net/docs/linux/linux-gcc.php
> 
> Signed-off-by: John Audia <therealgraysky@...ton.me>
> ---
>  arch/x86/Kconfig.cpu | 60 +++++++++++++++++++++++++++++++++++++++-----
>  arch/x86/Makefile    |  6 +++++
>  2 files changed, 60 insertions(+), 6 deletions(-)

Patches like this one appear off and on on the mailing list and each
time I ask what's the upside of maintaining this complexity?

And everytime I get no reply or random handwaving. That's because -march
settings have no noticeable effect on kernel code generation. Because
the kernel code is already pretty much optimized when generated by the
compiler and all those flavors don't bring anything additional.

So this is not going anywhere. But hey, I'm always open to nice
surprises...

Thx.

-- 
Regards/Gruss,
    Boris.

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