From: Linus Torvalds <torvalds@linux-foundation.org>
To: Vineet Gupta <Vineet.Gupta1@synopsys.com>
Cc: Arnd Bergmann <arnd@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Masahiro Yamada <masahiroy@kernel.org>,
Jann Horn <jannh@google.com>, lkml <linux-kernel@vger.kernel.org>,
arcml <linux-snps-arc@lists.infradead.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>
Subject: Re: Heads up: gcc miscompiling initramfs zlib decompression code at -O3
Date: Fri, 30 Apr 2021 15:52:52 -0700 [thread overview]
Message-ID: <CAHk-=wizZ-HoBJ24TPFawS5zHqT+HcreqfmFRf3Cw4SS0NxV+Q@mail.gmail.com> (raw)
In-Reply-To: <9538bb7e-a600-2211-6b4d-561b99f1deca@synopsys.com>
On Fri, Apr 30, 2021 at 3:44 PM Vineet Gupta <Vineet.Gupta1@synopsys.com> wrote:
>
> I agree that -O2 is default, but we've had -O3 default for ARC kernel
> forever, since last decade seriously. The reason I turned it on back
> then was upside of 10% performance improvement on select LMBench numbers
> on hardware at the time which for a rookie kernel hacker was yay momemt.
> I can revisit this and see if that is still true.
It would be interesting if you can actually show 10% improvement, and
also pinpoint things in the profile.
I (long long long ago) actually used -O6 for kernel builds as a "give
me everything you have" (I don't think gcc has actually ever done
anything more than O3, but whatever).
In fact, you can find
Q: What Does gcc -O6 Do?
in some kernel FAQ's from those historical times.
We eventually gave up on it, because it just generated bigger and
slower code, and people got very tired of all the compiler bugs.
Linus
next prev parent reply other threads:[~2021-04-30 22:53 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-30 20:46 Heads up: gcc miscompiling initramfs zlib decompression code at -O3 Vineet Gupta
2021-04-30 22:06 ` Linus Torvalds
2021-04-30 22:44 ` Vineet Gupta
2021-04-30 22:52 ` Linus Torvalds [this message]
2021-05-01 21:03 ` Oleksandr Natalenko
2021-05-03 17:41 ` Linus Torvalds
2021-05-03 19:18 ` Vineet Gupta
2021-05-05 17:44 ` Heiko Carstens
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAHk-=wizZ-HoBJ24TPFawS5zHqT+HcreqfmFRf3Cw4SS0NxV+Q@mail.gmail.com' \
--to=torvalds@linux-foundation.org \
--cc=Vineet.Gupta1@synopsys.com \
--cc=arnd@kernel.org \
--cc=jannh@google.com \
--cc=linux-arch@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-snps-arc@lists.infradead.org \
--cc=masahiroy@kernel.org \
--cc=peterz@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).