Re: [PATCH v7] pgo: add clang's Profile Guided Optimization infrastructure

Nick Desaulniers
2021-01-28T21:26:12Z

On Thu, Jan 28, 2021 at 1:19 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
>
> On Thu, Jan 28, 2021 at 10:12 PM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > On Thu, Jan 28, 2021 at 12:46 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
> > >
> > > [ LLVM ]
> > >
> > > Today, I switched over to LLVM version 12.0.0-rc1.
> > >
> > >
> > > [ Step #1: 5.11.0-rc5-5-amd64-clang12-pgo ]
> > >
> > > My first kernel was built with CONFIG_PGO_CLANG=y and LLVM=1 plus LLVM_IAS=1.
> > >
> > > [ start-build_5.11.0-rc5-5-amd64-clang12-pgo.txt ]
> > > dileks 193090 193065 0 06:54 pts/2 00:00:00 /usr/bin/perf_5.10
> > > stat make V=1 -j4 HOSTCC=clang HOSTCXX=clang++ HOSTLD=ld.lld CC=clang
> > > LD=ld.lld LLVM=1 LLVM_IAS=1 PAHOLE=/opt/pahole/bin/pahole
> > > LOCALVERSION=-5-amd64-clang12-pgo KBUILD_VERBOSE=1
> > > KBUILD_BUILD_HOST=iniza KBUILD_BUILD_USER=sedat.dilek@gmail.com
> > > KBUILD_BUILD_TIMESTAMP=2021-01-28 bindeb-pkg
> > > KDEB_PKGVERSION=5.11.0~rc5-5~bullseye+dileks1
> > >
> > > Config: config-5.11.0-rc5-5-amd64-clang12-pgo
> > >
> > >
> > > [ Step #2: x86-64 defconfig & vmlinux.profdata ]
> > >
> > > Booted into 5.11.0-rc5-5-amd64-clang12-pgo and built an x86-64
> > > defconfig to generate/merge a vmlinux.profdata file.
> > >
> > > [ start-build_x86-64-defconfig.txt ]
> > > dileks 18430 15640 0 11:15 pts/2 00:00:00 make V=1 -j4
> > > HOSTCC=clang HOSTCXX=clang++ HOSTLD=ld.lld CC=clang LD=ld.lld LLVM=1
> > > LLVM_IAS=1
> > >
> > > Script: profile_clang-pgo.sh
> > > Config: dot-config.x86-64-defconfig
> > >
> > >
> > > [ Step #3.1: 5.11.0-rc5-6-amd64-clang12-pgo & GNU-AS ]
> > >
> > > The first rebuild with CONFIG_PGO_CLANG=n and "LLVM=1
> > > KCFLAGS=-fprofile-use=vmlinux.profdata".
> > > I was able to boot into this one.
> > > Used assembler: GNU-AS 2.35.1
> > >
> > > [ start-build_5.11.0-rc5-6-amd64-clang12-pgo.txt ]
> > > dileks 65734 65709 0 11:54 pts/2 00:00:00 /usr/bin/perf_5.10
> > > stat make V=1 -j4 HOSTCC=clang HOSTCXX=clang++ HOSTLD=ld.lld CC=clang
> > > LD=ld.lld PAHOLE=/opt/pahole/bin/pahole
> > > LOCALVERSION=-6-amd64-clang12-pgo KBUILD_VERBOSE=1
> > > KBUILD_BUILD_HOST=iniza KBUILD_BUILD_USER=sedat.dilek@gmail.com
> > > KBUILD_BUILD_TIMESTAMP=2021-01-28 bindeb-pkg
> > > KDEB_PKGVERSION=5.11.0~rc5-6~bullseye+dileks1 LLVM=1
> > > KCFLAGS=-fprofile-use=vmlinux.profdata
> > >
> > > Config: config-5.11.0-rc5-6-amd64-clang12-pgo
> > >
> > >
> > > [ Step #3.2: 5.11.0-rc5-7-amd64-clang12-pgo & Clang-IAS ]
> > >
> > > The second rebuild with CONFIG_PGO_CLANG=n and "LLVM=1
> > > KCFLAGS=-fprofile-use=vmlinux.profdata" plus LLVM_IAS=1.
> > > Compilable but NOT bootable in QEMU and on bare metal.
> > > Used assembler: Clang-IAS v12.0.0-rc1
> > >
> > > [ start-build_5.11.0-rc5-7-amd64-clang12-pgo.txt ]
> > > dileks 6545 6520 0 16:31 pts/2 00:00:00 /usr/bin/perf_5.10
> > > stat make V=1 -j4 HOSTCC=clang HOSTCXX=clang++ HOSTLD=ld.lld CC=clang
> > > LD=ld.lld PAHOLE=/opt/pahole/bin/pahole
> > > LOCALVERSION=-7-amd64-clang12-pgo KBUILD_VERBOSE=1
> > > KBUILD_BUILD_HOST=iniza KBUILD_BUILD_USER=sedat.dilek@gmail.com
> > > KBUILD_BUILD_TIMESTAMP=2021-01-28 bindeb-pkg
> > > KDEB_PKGVERSION=5.11.0~rc5-7~bullseye+dileks1 LLVM=1
> > > KCFLAGS=-fprofile-use=vmlinux.profdata LLVM_IAS=1
> > >
> > > Config: config-5.11.0-rc5-7-amd64-clang12-pgo
> > >
> > >
> > > [ Conclusion ]
> > >
> > > The only statement I can tell you is a "PGO optimized" rebuild with
> > > LLVM_IAS=1 is compilable but NOT bootable.
> >
> > Thanks for the extensive testing and report. Can you compress, upload,
> > and post a link to your kernel image? I would like to take it for a
> > spin in QEMU and see if I can find what it's doing, then work
> > backwards from there.
> >
>
> Which files do you need?
> For QEMU: bzImage and initrd.img enough?

bzImage should be enough; I'll use my own initrd. If that boots for
me, maybe then I'll take a look with the initrd added.
--
Thanks,
~Nick Desaulniers