From: Bill Wendling <morbo@google.com>
To: Peter Zijlstra <peterz@infradead.org>
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 10:25:57 -0700 [thread overview]
Message-ID: <CAGG=3QXjD1DQjACu=CQQSP=whue-14Pw8FcNcXrJZfLC_E+y9w@mail.gmail.com> (raw)
In-Reply-To: <YMTn9yjuemKFLbws@hirez.programming.kicks-ass.net>
On Sat, Jun 12, 2021 at 9:59 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Wed, Apr 07, 2021 at 02:17:04PM -0700, Bill Wendling 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 now be used by the compiler:
> >
> > $ make LLVM=1 KCFLAGS=-fprofile-use=vmlinux.profdata ...
> >
> > This initial submission is restricted to x86, as that's the platform we
> > know works. This restriction can be lifted once other platforms have
> > been verified to work with PGO.
>
> *sigh*, and not a single x86 person on Cc, how nice :-/
>
This tool is generic and, despite the fact that it's first enabled for
x86, it contains no x86-specific code. The reason we're restricting it
to x86 is because it's the platform we tested on.
> > Note that this method of profiling the kernel is clang-native, unlike
> > the clang support in kernel/gcov.
> >
> > [1] https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization
>
> Also, and I don't see this answered *anywhere*, why are you not using
> perf for this? Your link even mentions Sampling Profilers (and I happen
> to know there's been significant effort to make perf output work as
> input for the PGO passes of the various compilers).
>
Instruction-based (non-sampling) profiling gives us a better
context-sensitive profile, making PGO more impactful. It's also useful
for coverage whereas sampling profiles cannot.
> > Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> > Co-developed-by: Bill Wendling <morbo@google.com>
> > Signed-off-by: Bill Wendling <morbo@google.com>
> > Tested-by: Nick Desaulniers <ndesaulniers@google.com>
> > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> > Reviewed-by: Fangrui Song <maskray@google.com>
> > ---
> > Documentation/dev-tools/index.rst | 1 +
> > Documentation/dev-tools/pgo.rst | 127 +++++++++
> > MAINTAINERS | 9 +
> > Makefile | 3 +
> > arch/Kconfig | 1 +
> > arch/x86/Kconfig | 1 +
> > arch/x86/boot/Makefile | 1 +
> > arch/x86/boot/compressed/Makefile | 1 +
> > arch/x86/crypto/Makefile | 4 +
> > arch/x86/entry/vdso/Makefile | 1 +
> > arch/x86/kernel/vmlinux.lds.S | 2 +
> > arch/x86/platform/efi/Makefile | 1 +
> > arch/x86/purgatory/Makefile | 1 +
> > arch/x86/realmode/rm/Makefile | 1 +
> > arch/x86/um/vdso/Makefile | 1 +
> > drivers/firmware/efi/libstub/Makefile | 1 +
> > include/asm-generic/vmlinux.lds.h | 34 +++
> > kernel/Makefile | 1 +
> > kernel/pgo/Kconfig | 35 +++
> > kernel/pgo/Makefile | 5 +
> > kernel/pgo/fs.c | 389 ++++++++++++++++++++++++++
> > kernel/pgo/instrument.c | 189 +++++++++++++
> > kernel/pgo/pgo.h | 203 ++++++++++++++
> > scripts/Makefile.lib | 10 +
> > 24 files changed, 1022 insertions(+)
> > create mode 100644 Documentation/dev-tools/pgo.rst
> > create mode 100644 kernel/pgo/Kconfig
> > create mode 100644 kernel/pgo/Makefile
> > create mode 100644 kernel/pgo/fs.c
> > create mode 100644 kernel/pgo/instrument.c
> > create mode 100644 kernel/pgo/pgo.h
>
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -660,6 +660,9 @@ endif # KBUILD_EXTMOD
> > # Defaults to vmlinux, but the arch makefile usually adds further targets
> > all: vmlinux
> >
> > +CFLAGS_PGO_CLANG := -fprofile-generate
> > +export CFLAGS_PGO_CLANG
> > +
> > CFLAGS_GCOV := -fprofile-arcs -ftest-coverage \
> > $(call cc-option,-fno-tree-loop-im) \
> > $(call cc-disable-warning,maybe-uninitialized,)
>
> And which of the many flags in noinstr disables this?
>
These flags aren't used with PGO. So there's no need to disable them.
> Basically I would like to NAK this whole thing until someone can
> adequately explain the interaction with noinstr and why we need those
> many lines of kernel code and can't simply use perf for this.
-bw
next prev parent reply other threads:[~2021-06-12 17:26 UTC|newest]
Thread overview: 123+ 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 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 [this message]
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
2021-06-01 18:53 Kees Cook
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