From: Peter Zijlstra <peterz@infradead.org>
To: Bill Wendling <morbo@google.com>
Cc: Kees Cook <keescook@google.com>, Jonathan Corbet <corbet@lwn.net>,
Masahiro Yamada <masahiroy@kernel.org>,
Linux Doc Mailing List <linux-doc@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
clang-built-linux <clang-built-linux@googlegroups.com>,
Andrew Morton <akpm@linux-foundation.org>,
Nathan Chancellor <natechancellor@gmail.com>,
Nick Desaulniers <ndesaulniers@google.com>,
Sami Tolvanen <samitolvanen@google.com>,
Fangrui Song <maskray@google.com>,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel.org>
Subject: Re: [PATCH v9] pgo: add clang's Profile Guided Optimization infrastructure
Date: Sat, 12 Jun 2021 22:25:05 +0200 [thread overview]
Message-ID: <20210612202505.GG68208@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <CAGG=3QVHkkJ236mCJ8Jt_6JtgYtWHV9b4aVXnoj6ypc7GOnc0A@mail.gmail.com>
On Sat, Jun 12, 2021 at 12:10:03PM -0700, Bill Wendling wrote:
> > You're modifying a lot of x86 files, you don't think it's good to let us
> > know? Worse, afaict this -fprofile-generate changes code generation,
> > and we definitely want to know about that.
> >
> I got the list of people to add from the scripts/get_maintainer.pl.
$ ./scripts/get_maintainer.pl -f arch/x86/Makefile
Thomas Gleixner <tglx@linutronix.de> (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT))
Ingo Molnar <mingo@redhat.com> (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT))
Borislav Petkov <bp@alien8.de> (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT))
x86@kernel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT))
> there's one intel people CC'ed, but he didn't sign off on it.
Intel does not employ the main x86 maintainers, even it if did, mailing
a random Google person won't get the mail to you either, would it?
> These patches were available for review for months now,
Which doesn't help if you don't Cc the right people, does it. *nobody*
has time to read LKML.
> and posted to all of the lists and CC'ed to the people from
> scripts/get_maintainers.pl. Perhaps that program should be improved?
I suspect operator error, see above.
> > Supposedly -fprofile-generate adds instrumentation to the generated
> > code. noinstr *MUST* disable that. If not, this is a complete
> > non-starter for x86.
>
> "noinstr" has "notrace", which is defined as
> "__attribute__((__no_instrument_function__))", which is honored by
> both gcc and clang.
Yes it is, but is that sufficient in this case? It very much isn't for
KASAN, UBSAN, and a whole host of other instrumentation crud. They all
needed their own 'bugger-off' attributes.
> > We've got KCOV and GCOV support already. Coverage is also not an
> > argument mentioned anywhere else. Coverage can go pound sand, we really
> > don't need a third means of getting that.
> >
> Those aren't useful for clang-based implementations. And I like to
> look forward to potential improvements.
I look forward to less things doing the same over and over. The obvious
solution if of course to make clang use what we have, not the other way
around.
> > Do you have actual numbers that back up the sampling vs instrumented
> > argument? Having the instrumentation will affect performance which can
> > scew the profile just the same.
> >
> Instrumentation counts the number of times a branch is taken. Sampling
> is at a gross level, where if the sampling time is fine enough, you
> can get an idea of where the hot spots are, but it won't give you the
> fine-grained information that clang finds useful. Essentially, while
> sampling can "capture the hot spots very well", relying solely on
> sampling is basically leaving optimization on the floor.
>
> Our optimizations experts here have determined, through data of
> course, that instrumentation is the best option for PGO.
It would be very good to post some of that data and explicit examples.
Hear-say don't carry much weight.
next prev parent reply other threads:[~2021-06-12 20:25 UTC|newest]
Thread overview: 124+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-11 8:18 [PATCH] pgo: add clang's Profile Guided Optimization infrastructure Bill Wendling
2021-01-11 8:39 ` Sedat Dilek
2021-01-11 8:42 ` Sedat Dilek
2021-01-11 9:17 ` Bill Wendling
2021-01-11 9:57 ` Sedat Dilek
2021-01-11 18:28 ` Nathan Chancellor
2021-01-11 20:12 ` Fangrui Song
2021-01-11 20:23 ` Bill Wendling
2021-01-11 20:31 ` Fangrui Song
2021-01-12 0:37 ` Bill Wendling
2021-01-12 0:44 ` Fāng-ruì Sòng
2021-01-11 21:04 ` Nathan Chancellor
2021-01-11 21:17 ` Nick Desaulniers
2021-01-11 21:32 ` Bill Wendling
2021-01-12 5:14 ` [PATCH v2] " Bill Wendling
2021-01-12 5:17 ` Sedat Dilek
2021-01-12 5:31 ` [PATCH v3] " Bill Wendling
2021-01-12 9:10 ` kernel test robot
2021-01-12 9:10 ` kernel test robot
2021-01-12 17:22 ` Nathan Chancellor
2021-01-13 6:19 ` [PATCH v4] " Bill Wendling
2021-01-13 20:55 ` Nathan Chancellor
2021-01-13 21:59 ` Bill Wendling
2021-01-14 4:07 ` Nick Desaulniers
2021-01-16 0:01 ` Nick Desaulniers
2021-01-16 0:13 ` Nick Desaulniers
2021-01-16 4:30 ` Sedat Dilek
2021-01-16 5:07 ` Sedat Dilek
2021-01-16 5:18 ` Sedat Dilek
2021-01-18 0:57 ` Sedat Dilek
2021-01-13 23:01 ` Nick Desaulniers
2021-01-16 9:43 ` [PATCH v5] " Bill Wendling
2021-01-16 17:38 ` Sedat Dilek
2021-01-16 18:36 ` Sedat Dilek
2021-01-16 20:23 ` Bill Wendling
2021-01-17 10:44 ` Sedat Dilek
2021-01-17 10:53 ` Sedat Dilek
2021-01-17 11:23 ` Sedat Dilek
2021-01-17 11:42 ` Sedat Dilek
2021-01-17 11:58 ` Sedat Dilek
2021-01-17 12:05 ` Sedat Dilek
2021-01-17 17:42 ` Sedat Dilek
2021-01-17 20:34 ` Bill Wendling
2021-01-17 23:33 ` Sedat Dilek
2021-01-18 0:26 ` Sedat Dilek
2021-01-18 2:32 ` Bill Wendling
2021-01-18 12:39 ` Sedat Dilek
2021-01-18 17:26 ` Sedat Dilek
2021-01-18 21:56 ` Bill Wendling
2021-01-18 23:29 ` Sedat Dilek
2021-01-21 2:03 ` Sedat Dilek
2021-01-21 22:44 ` Sedat Dilek
2021-01-22 1:42 ` Nick Desaulniers
2021-01-22 1:49 ` Sedat Dilek
2021-01-22 1:52 ` Nick Desaulniers
2021-01-22 1:54 ` Sedat Dilek
2021-01-20 1:02 ` Nick Desaulniers
2021-01-21 0:51 ` Nick Desaulniers
2021-01-21 8:24 ` Bill Wendling
2021-01-21 8:24 ` [PATCH v6] " Bill Wendling
2021-01-21 10:34 ` Sedat Dilek
2021-01-22 1:44 ` Nick Desaulniers
2021-01-22 1:51 ` Sedat Dilek
2021-01-22 0:14 ` Sedat Dilek
2021-01-22 0:58 ` Sedat Dilek
2021-01-22 1:29 ` Nick Desaulniers
2021-01-22 10:11 ` [PATCH v7] " Bill Wendling
2021-01-22 11:31 ` Sedat Dilek
2021-01-22 18:41 ` Nick Desaulniers
2021-01-28 20:46 ` Sedat Dilek
2021-01-28 21:12 ` Nick Desaulniers
2021-01-28 21:19 ` Sedat Dilek
2021-01-28 21:24 ` Nick Desaulniers
2021-01-28 21:39 ` Sedat Dilek
2021-01-29 7:43 ` Sedat Dilek
2021-01-29 21:48 ` Nick Desaulniers
2021-02-10 23:25 ` Bill Wendling
2021-02-22 21:52 ` Bill Wendling
2021-02-26 22:20 ` [PATCH v8] " Bill Wendling
2021-02-26 22:55 ` Bill Wendling
2021-02-28 18:52 ` Fangrui Song
2021-02-28 21:50 ` Fangrui Song
2021-01-12 17:37 ` [PATCH v2] " Nick Desaulniers
2021-01-12 17:45 ` Fāng-ruì Sòng
2021-01-21 2:21 ` [PATCH] " Sedat Dilek
2021-01-22 1:34 ` Nick Desaulniers
2021-01-22 1:43 ` Sedat Dilek
2021-04-07 21:17 ` [PATCH v9] " Bill Wendling
2021-04-07 21:22 ` Kees Cook
2021-04-07 21:44 ` Fāng-ruì Sòng
2021-04-07 21:47 ` Nathan Chancellor
2021-04-07 21:58 ` Bill Wendling
2021-05-19 21:37 ` Kees Cook
2021-05-22 23:51 ` Bill Wendling
2021-05-31 21:12 ` Nathan Chancellor
2021-06-01 17:31 ` Nick Desaulniers
2021-06-12 16:59 ` Peter Zijlstra
2021-06-12 17:25 ` Bill Wendling
2021-06-12 18:15 ` Peter Zijlstra
2021-06-12 19:10 ` Bill Wendling
2021-06-12 19:28 ` Bill Wendling
2021-06-12 20:25 ` Peter Zijlstra [this message]
2021-06-12 20:56 ` Bill Wendling
2021-06-12 22:47 ` Bill Wendling
2021-06-13 18:07 ` Bill Wendling
2021-06-14 9:43 ` Peter Zijlstra
2021-06-14 10:18 ` Peter Zijlstra
2021-06-14 7:51 ` Peter Zijlstra
2021-06-14 9:01 ` Peter Zijlstra
2021-06-14 9:39 ` Bill Wendling
2021-06-14 10:44 ` Peter Zijlstra
2021-06-14 11:41 ` Bill Wendling
2021-06-14 11:43 ` Bill Wendling
2021-06-14 14:16 ` Marco Elver
2021-06-14 15:26 ` Kees Cook
2021-06-14 15:35 ` Peter Zijlstra
2021-06-14 16:22 ` Kees Cook
2021-06-14 18:07 ` Nick Desaulniers
2021-06-14 20:49 ` Nick Desaulniers
2021-06-14 15:46 ` Peter Zijlstra
2021-06-14 16:03 ` Nick Desaulniers
2021-06-12 20:20 ` Fangrui Song
2021-06-12 20:31 ` Peter Zijlstra
-- strict thread matches above, loose matches on Subject: below --
2021-06-01 18:53 Kees Cook
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