linux-kernel - Re: [PATCH] Kconfig: default to CC_OPTIMIZE_FOR_PERFORMANCE

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Message-ID: <CAK8P3a06DmZr4cJt=v+1uT4sT-E3yWkeg-YioyjK3GZR5Twunw@mail.gmail.com>
Date:   Fri, 8 May 2020 15:04:25 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Oleksandr Natalenko <oleksandr@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] Kconfig: default to CC_OPTIMIZE_FOR_PERFORMANCE_O3 for
 gcc >= 10

On Fri, May 8, 2020 at 2:07 PM Jason A. Donenfeld <Jason@...c4.com> wrote:
> On Fri, May 8, 2020 at 5:56 AM Arnd Bergmann <arnd@...db.de> wrote:
>
> The other significant thing -- and what prompted this patchset -- is
> it looks like gcc 10 has lowered the inlining degree for -O2, and put
> gcc 9's inlining parameters from -O2 into gcc-10's -O3.

I suspect it is more complicated than that, as there are a number of
parameters that determine inlining decisions. It's also not clear whether
the ones for -O3 are generally better than the ones with -O2, or if it's
just that whatever changed caused a few surprises but is otherwise
preferable.

Did you see regressions in specific modules, or just a general slowdown
or growth in object size as the result?

      Arnd