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From:   Linus Torvalds <linus@linux-foundation.org>
Date:   Fri, 24 Jun 2022 11:29:49 -0700
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Subject: Re: [PATCH 0/2] Kconfig: -O3 enablement
To:     arnd@arndb.de
Cc:     bigeasy@linutronix.de, chris@chrisdown.name,
        dmitry.torokhov@gmail.com, gustavoars@kernel.org,
        john.ogness@linutronix.de, linux-kbuild@vger.kernel.org,
        linux-kernel@vger.kernel.org, masahiroy@kernel.org,
        mikoxyzzz@gmail.com, nathan@kernel.org, ndesaulniers@google.com,
        oleksandr@redhat.com, quic_eberman@quicinc.com, seanjc@google.com,
        tglx@linutronix.de, vbabka@suse.cz, x86@kernel.org
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On Thu, Jun 23 at 7:27:29 PM  Arnd Bergmann <arnd@arndb.de> wrote:
>
> This probably also needs a dependency on !COMPILE_TEST so we don't
> report compile-time problems that are specific to -O3.

Honestly, let's just remove -O3 entirely.

Enabling it, and then not even build-testing the result, is just about
the *worst* possible case. That's just horrible.

The argument that "but ARC uses it" is not an argument. It was always
a bad argument, and ARC needs to just fix whatever it is that made it
an issue (likely already fixed with a compiler upgrade).

And there is no way I would ever accept this as a "let people try it" when

 - as mentioned, just use KCFLAGS=-O3 if you want to

 - -O3 has a *loong* history of generating worse code than -O2

so I will *not* be taking these kinds of patches without some very
serious explanations of why -O3 has suddenly become acceptable again.

Those explanations had better be more than "let people try". They
should have in-depth actual performance numbers for a real load, not
some made-up "bigger is better" logic.

                 Linus