From: Bill Wendling <morbo@google.com>
To: Fangrui Song <maskray@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>,
Masahiro Yamada <masahiroy@kernel.org>,
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>
Subject: Re: [PATCH] pgo: add clang's Profile Guided Optimization infrastructure
Date: Mon, 11 Jan 2021 12:23:08 -0800 [thread overview]
Message-ID: <CAGG=3QWo5_wwTMHtif4BzFssByaW1ScvpaEH1p1nZ6ymVggLjA@mail.gmail.com> (raw)
In-Reply-To: <20210111201224.l5r2zxuyd7ayszke@google.com>
On Mon, Jan 11, 2021 at 12:12 PM Fangrui Song <maskray@google.com> wrote:
>
> On 2021-01-11, 'Bill Wendling' via Clang Built Linux wrote:
> >From: Sami Tolvanen <samitolvanen@google.com>
> >
> >Enable the use of clang's Profile-Guided Optimization[1]. To generate a
> >profile, the kernel is instrumented with PGO counters, a representative
> >workload is run, and the raw profile data is collected from
> >/sys/kernel/debug/pgo/profraw.
> >
> >The raw profile data must be processed by clang's "llvm-profdata" tool before
> >it can be used during recompilation:
> >
> > $ cp /sys/kernel/debug/pgo/profraw vmlinux.profraw
> > $ llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> >
> >Multiple raw profiles may be merged during this step.
> >
> >The data can be used either by the compiler if LTO isn't enabled:
> >
> > ... -fprofile-use=vmlinux.profdata ...
> >
> >or by LLD if LTO is enabled:
> >
> > ... -lto-cs-profile-file=vmlinux.profdata ...
>
> This LLD option does not exist.
> LLD does have some `--lto-*` options but the `-lto-*` form is not supported
> (it clashes with -l) https://reviews.llvm.org/D79371
>
That's strange. I've been using that option for years now. :-) Is this
a recent change?
> (There is an earlier -fprofile-instr-generate which does
> instrumentation in Clang, but the option does not have broad usage.
> It is used more for code coverage, not for optimization.
> Noticeably, it does not even implement the Kirchhoff's current law
> optimization)
>
Right. I've been told outside of this email that -fprofile-generate is
the prefered flag to use.
> -fprofile-use= is used by both regular PGO and context-sensitive PGO (CSPGO).
>
> clang -flto=thin -fprofile-use= passes -plugin-opt=cs-profile-path= to the linker.
> For regular PGO, this option is effectively a no-op (confirmed with CSPGO main developer).
>
> So I think the "or by LLD if LTO is enabled:" part should be removed.
But what if you specify the linking step explicitly? Linux doesn't
call "clang" when linking, but "ld.lld".
-bw
next prev parent reply other threads:[~2021-01-11 20:25 UTC|newest]
Thread overview: 116+ 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 [this message]
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
[not found] ` <202101121755.pyYoRozB-lkp@intel.com>
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
[not found] ` <CA+icZUXmn15w=kSq2CZzQD5JggJw_9AEam=Sz13M0KpJ68MWZg@mail.gmail.com>
2021-01-17 17:42 ` Sedat Dilek
2021-01-17 20:34 ` Bill Wendling
[not found] ` <CA+icZUU1HihUFaEHzF69+01+Picg8aq6HAqHupxiRqyDGJ=Mpw@mail.gmail.com>
[not found] ` <CA+icZUUuzA5JEXyVzKbVX+T3xeOdRAU6-mntbo+VwwTxqmN7LA@mail.gmail.com>
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
2021-01-20 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
[not found] ` <CA+icZUU=XfwqMcXYonQKcD4QgqTBW-mA+d_84b7cU2R3HYPOSQ@mail.gmail.com>
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
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
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='CAGG=3QWo5_wwTMHtif4BzFssByaW1ScvpaEH1p1nZ6ymVggLjA@mail.gmail.com' \
--to=morbo@google.com \
--cc=akpm@linux-foundation.org \
--cc=clang-built-linux@googlegroups.com \
--cc=corbet@lwn.net \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kbuild@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=masahiroy@kernel.org \
--cc=maskray@google.com \
--cc=natechancellor@gmail.com \
--cc=ndesaulniers@google.com \
--cc=samitolvanen@google.com \
/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).