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From: Linus Torvalds <linus@linux-foundation.org>
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
Subject: Re: [PATCH 0/2] Kconfig: -O3 enablement
Date: Fri, 24 Jun 2022 11:29:49 -0700	[thread overview]
Message-ID: <CA+55aFz2sNBbZyg-_i8_Ldr2e8o9dfvdSfHHuRzVtP2VMAUWPg@mail.gmail.com> (raw)

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

             reply	other threads:[~2022-06-24 18:30 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-24 18:29 Linus Torvalds [this message]
     [not found] ` <CA+55aFyugRmHNV1BbhB_YHf3mgaiU6ND_KL8bu0PPEaRVNwWHg@mail.gmail.com>
2022-06-24 18:38   ` Linus Torvalds
2022-06-28 21:04 ` [PATCH] kbuild: drop support for CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 Nick Desaulniers
2022-06-29 10:48   ` Miko Larsson
2022-07-11  5:50     ` Masahiro Yamada
2022-07-11  5:05   ` Masahiro Yamada
  -- strict thread matches above, loose matches on Subject: below --
2022-06-21 13:35 [PATCH 0/2] Kconfig: -O3 enablement Miko Larsson
2022-06-21 16:16 ` Nick Desaulniers
2022-06-22  1:57   ` Masahiro Yamada
2022-06-23 15:42     ` Miko Larsson
2022-06-23 15:44       ` Masahiro Yamada
2022-06-23 17:00         ` Miko Larsson
2022-06-23 17:15           ` Masahiro Yamada
2022-06-23 17:44             ` Miko Larsson
2022-06-23 17:27     ` Arnd Bergmann

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