linux-doc.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
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

  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).