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Message-ID: <e4dad58c-e329-4e9a-aa6f-8b08bdf8f350@cachyos.org>
Date: Tue, 5 Nov 2024 15:56:51 +0100
From: Peter Jung <ptr1337@...hyos.org>
To: Rong Xu <xur@...gle.com>, Han Shen <shenhan@...gle.com>
Cc: Alice Ryhl <aliceryhl@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>, Arnd Bergmann <arnd@...db.de>,
Bill Wendling <morbo@...gle.com>, Borislav Petkov <bp@...en8.de>,
Breno Leitao <leitao@...ian.org>, Brian Gerst <brgerst@...il.com>,
Dave Hansen <dave.hansen@...ux.intel.com>, David Li <davidxl@...gle.com>,
Heiko Carstens <hca@...ux.ibm.com>, "H. Peter Anvin" <hpa@...or.com>,
Ingo Molnar <mingo@...hat.com>, Jann Horn <jannh@...gle.com>,
Jonathan Corbet <corbet@....net>, Josh Poimboeuf <jpoimboe@...nel.org>,
Juergen Gross <jgross@...e.com>, Justin Stitt <justinstitt@...gle.com>,
Kees Cook <kees@...nel.org>, Masahiro Yamada <masahiroy@...nel.org>,
"Mike Rapoport (IBM)" <rppt@...nel.org>,
Nathan Chancellor <nathan@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Nicolas Schier <nicolas@...sle.eu>, "Paul E. McKenney" <paulmck@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
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<tglx@...utronix.de>, Wei Yang <richard.weiyang@...il.com>,
workflows@...r.kernel.org, Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
Maksim Panchenko <max4bolt@...il.com>, "David S. Miller"
<davem@...emloft.net>, Andreas Larsson <andreas@...sler.com>,
Yonghong Song <yonghong.song@...ux.dev>, Yabin Cui <yabinc@...gle.com>,
Krzysztof Pszeniczny <kpszeniczny@...gle.com>,
Sriraman Tallam <tmsriram@...gle.com>, Stephane Eranian
<eranian@...gle.com>, x86@...nel.org, linux-arch@...r.kernel.org,
sparclinux@...r.kernel.org, linux-doc@...r.kernel.org,
linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
llvm@...ts.linux.dev
Subject: Re: [PATCH v7 1/7] Add AutoFDO support for Clang build
You were right - reverting commit:
https://github.com/bminor/binutils-gdb/commit/b20ab53f81db7eefa0db00d14f06c04527ac324c
from the 2.43 branch does fix the packaging.
I will forward this to an issue at their bugzilla.
On 05.11.24 15:33, Peter Jung wrote:
> Hi Rong,
>
> Glad that you were able to reproduce the issue!
> Thanks for finding the root cause as well as the part of the code. This
> really helps.
>
> I was able to do a successful packaging with binutils 2.42.
> Lets forward this to the binutils tracker and hope this will be soon
> solved. 🙂
>
> I have tested this also on the latest commit
> (e1e4078ac59740a79cd709d61872abe15aba0087) and the issue is also
> reproducible there.
>
> Thanks for your time! I dont see this as blocker. 🙂
> It gets time to get this series merged :P
>
> Best regards,
>
> Peter
>
>
>
> On 05.11.24 08:25, Rong Xu wrote:
>> We debugged this issue and we found the failure seems to only happen
>> with strip (version 2.43) in binutil.
>>
>> For a profile-use compilation, either with -fprofile-use (PGO or
>> iFDO), or -fprofile-sample-use (AutoFDO),
>> an ELF section of .llvm.call-graph-profile is created for the object.
>> For some reasons (like to save space?),
>> the relocations in this section are of type "rel', rather the more
>> common "rela" type.
>>
>> In this case,
>> $ readelf -r kvm.ko |grep llvm.call-graph-profile
>> Relocation section '.rel.llvm.call-graph-profile' at offset 0xf62a00
>> contains 4 entries:
>>
>> strip (v2.43.0) has difficulty handling the relocations in
>> .rel.llvm.call-graph-profile -- it silently failed with --strip-debug.
>> But strip (v.2.42) has no issue with kvm.ko. The strip in llvm (i.e.
>> llvm-strip) also passes with kvm.ko
>>
>> I compared binutil/strip source code for version v2.43.0 and v2.42.
>> The different is around here:
>> In v2.42 of bfd/elfcode.h
>> Â Â Â 1618Â Â Â Â Â Â if ((entsize == sizeof (Elf_External_Rela)
>> Â Â Â 1619Â Â Â Â Â Â Â Â Â Â Â && ebd->elf_info_to_howto != NULL)
>> Â Â Â 1620Â Â Â Â Â Â Â Â Â Â || ebd->elf_info_to_howto_rel == NULL)
>> Â Â Â 1621Â Â Â Â Â Â Â Â res = ebd->elf_info_to_howto (abfd, relent, &rela);
>> Â Â Â 1622Â Â Â Â Â Â else
>> Â Â Â 1623Â Â Â Â Â Â Â Â res = ebd->elf_info_to_howto_rel (abfd, relent, &rela);
>>
>> In v2.43.0 of bfd/elfcode.h
>> Â Â Â 1618Â Â Â Â Â Â if (entsize == sizeof (Elf_External_Rela)
>> Â Â Â 1619Â Â Â Â Â Â Â Â Â Â && ebd->elf_info_to_howto != NULL)
>> Â Â Â 1620Â Â Â Â Â Â Â Â res = ebd->elf_info_to_howto (abfd, relent, &rela);
>> Â Â Â 1621Â Â Â Â Â Â else if (ebd->elf_info_to_howto_rel != NULL)
>> Â Â Â 1622Â Â Â Â Â Â Â Â res = ebd->elf_info_to_howto_rel (abfd, relent, &rela);
>>
>> In the 2.43 strip, line 1618 is false and line 1621 is also false.
>> "res" is returned as false and the program exits with -1.
>>
>> While in 2.42, line 1620 is true and we get "res" from line 1621 and
>> program functions correctly.
>>
>> I'm not familiar with binutil code base and don't know the reason for
>> removing line 1620.
>> I can file a bug for binutil for people to further investigate this.
>>
>> It seems to me that this issue should not be a blocker for our patch.
>>
>> Regards,
>>
>> -Rong
>>
>>
>>
>>
>>
>> On Mon, Nov 4, 2024 at 12:24 PM Han Shen<shenhan@...gle.com> wrote:
>>> Hi Peter,
>>> Thanks for providing the detailed reproduce.
>>> Now I can see the error (after I synced to 6.12.0-rc6, I was using rc5).
>>> I'll look into that and report back.
>>>
>>>> I have tested your provided method, but the AutoFDO profile (lld does
>>> not get lto-sample-profile=$pathtoprofile passed)
>>>
>>> I see. You also turned on ThinLTO, which I didn't, so the profile was
>>> only used during compilation, not passed to lld.
>>>
>>> Thanks,
>>> Han
>>>
>>> On Mon, Nov 4, 2024 at 9:31 AM Peter Jung<ptr1337@...hyos.org> wrote:
>>>> Hi Han,
>>>>
>>>> I have tested your provided method, but the AutoFDO profile (lld does
>>>> not get lto-sample-profile=$pathtoprofile passed)Â nor Clang as
>>>> compiler
>>>> gets used.
>>>> Please replace following PKGBUILD and config from linux-mainline with
>>>> the provided one in the gist. The patch is also included there.
>>>>
>>>> https://gist.github.com/ptr1337/c92728bb273f7dbc2817db75eedec9ed
>>>>
>>>> The main change I am doing here, is passing following to the build
>>>> array
>>>> and replacing "make all":
>>>>
>>>> make LLVM=1 LLVM_IAS=1 CLANG_AUTOFDO_PROFILE=${srcdir}/perf.afdo all
>>>>
>>>> When compiling the kernel with makepkg, this results at the
>>>> packaging to
>>>> following issue and can be reliable reproduced.
>>>>
>>>> Regards,
>>>>
>>>> Peter
>>>>
>>>>
>>>> On 04.11.24 05:50, Han Shen wrote:
>>>>> Hi Peter, thanks for reporting the issue. I am trying to reproduce it
>>>>> in the up-to-date archlinux environment. Below is what I have:
>>>>> Â Â Â 0. pacman -Syu
>>>>> Â Â Â 1. cloned archlinux build files from
>>>>> https://aur.archlinux.org/linux-mainline.git the newest mainline
>>>>> version is 6.12rc5-1.
>>>>> Â Â Â 2. changed the PKGBUILD file to include the patches series
>>>>> Â Â Â 3. changed the "config" to turn on clang autofdo
>>>>> Â Â Â 4. collected afdo profiles
>>>>> Â Â Â 5. MAKEFLAGS="-j48 V=1 LLVM=1 CLANG_AUTOFDO_PROFILE=$(pwd)/
>>>>> perf.afdo" \
>>>>> Â Â Â Â Â Â Â Â Â makepkg -s --skipinteg --skippgp
>>>>> Â Â Â 6. install and reboot
>>>>> The above steps succeeded.
>>>>> You mentioned the error happens at "module_install", can you instruct
>>>>> me how to execute the "module_install" step?
>>>>>
>>>>> Thanks,
>>>>> Han
>>>>>
>>>>> On Sat, Nov 2, 2024 at 12:53 PM Peter Jung<ptr1337@...hyos.org> wrote:
>>>>>>
>>>>>> On 02.11.24 20:46, Peter Jung wrote:
>>>>>>> On 02.11.24 18:51, Rong Xu wrote:
>>>>>>>> Add the build support for using Clang's AutoFDO. Building the
>>>>>>>> kernel
>>>>>>>> with AutoFDO does not reduce the optimization level from the
>>>>>>>> compiler. AutoFDO uses hardware sampling to gather information
>>>>>>>> about
>>>>>>>> the frequency of execution of different code paths within a binary.
>>>>>>>> This information is then used to guide the compiler's optimization
>>>>>>>> decisions, resulting in a more efficient binary. Experiments
>>>>>>>> showed that the kernel can improve up to 10% in latency.
>>>>>>>>
>>>>>>>> The support requires a Clang compiler after LLVM 17. This
>>>>>>>> submission
>>>>>>>> is limited to x86 platforms that support PMU features like LBR on
>>>>>>>> Intel machines and AMD Zen3 BRS. Support for SPE on ARM 1,
>>>>>>>> Â Â Â and BRBE on ARM 1 is part of planned future work.
>>>>>>>>
>>>>>>>> Here is an example workflow for AutoFDO kernel:
>>>>>>>>
>>>>>>>> 1) Build the kernel on the host machine with LLVM enabled, for
>>>>>>>> example,
>>>>>>>> Â Â Â Â Â Â Â Â Â $ make menuconfig LLVM=1
>>>>>>>> Â Â Â Â Â Â Turn on AutoFDO build config:
>>>>>>>> Â Â Â Â Â Â Â Â CONFIG_AUTOFDO_CLANG=y
>>>>>>>> Â Â Â Â Â Â With a configuration that has LLVM enabled, use the
>>>>>>>> following
>>>>>>>> Â Â Â Â Â Â command:
>>>>>>>> Â Â Â Â Â Â Â Â Â scripts/config -e AUTOFDO_CLANG
>>>>>>>> Â Â Â Â Â Â After getting the config, build with
>>>>>>>> Â Â Â Â Â Â Â Â $ make LLVM=1
>>>>>>>>
>>>>>>>> 2) Install the kernel on the test machine.
>>>>>>>>
>>>>>>>> 3) Run the load tests. The '-c' option in perf specifies the sample
>>>>>>>>      event period. We suggest    using a suitable prime number,
>>>>>>>> Â Â Â Â Â like 500009, for this purpose.
>>>>>>>> Â Â Â Â Â For Intel platforms:
>>>>>>>> Â Â Â Â Â Â Â Â $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c
>>>>>>>> <count> \
>>>>>>>> Â Â Â Â Â Â Â Â Â Â -o <perf_file> -- <loadtest>
>>>>>>>> Â Â Â Â Â For AMD platforms:
>>>>>>>> Â Â Â Â Â Â Â Â The supported system are: Zen3 with BRS, or Zen4 with
>>>>>>>> amd_lbr_v2
>>>>>>>> Â Â Â Â Â Â Â For Zen3:
>>>>>>>> Â Â Â Â Â Â Â Â $ cat proc/cpuinfo | grep " brs"
>>>>>>>> Â Â Â Â Â Â Â Â For Zen4:
>>>>>>>> Â Â Â Â Â Â Â Â $ cat proc/cpuinfo | grep amd_lbr_v2
>>>>>>>> Â Â Â Â Â Â Â Â $ perf record --pfm-events
>>>>>>>> RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k
>>>>>>>> -a \
>>>>>>>> Â Â Â Â Â Â Â Â Â Â -N -b -c <count> -o <perf_file> -- <loadtest>
>>>>>>>>
>>>>>>>> 4) (Optional) Download the raw perf file to the host machine.
>>>>>>>>
>>>>>>>> 5) To generate an AutoFDO profile, two offline tools are available:
>>>>>>>> Â Â Â Â Â create_llvm_prof and llvm_profgen. The create_llvm_prof
>>>>>>>> tool is part
>>>>>>>> Â Â Â Â Â of the AutoFDO project and can be found on GitHub
>>>>>>>> Â Â Â Â Â (https://github.com/google/autofdo), version v0.30.1 or
>>>>>>>> later. The
>>>>>>>> Â Â Â Â Â llvm_profgen tool is included in the LLVM compiler itself.
>>>>>>>> It's
>>>>>>>> Â Â Â Â Â important to note that the version of llvm_profgen doesn't
>>>>>>>> need to
>>>>>>>> Â Â Â Â Â match the version of Clang. It needs to be the LLVM 19
>>>>>>>> release or
>>>>>>>> Â Â Â Â Â later, or from the LLVM trunk.
>>>>>>>> Â Â Â Â Â Â Â Â $ llvm-profgen --kernel --binary=<vmlinux> --
>>>>>>>> perfdata=<perf_file> \
>>>>>>>> Â Â Â Â Â Â Â Â Â Â -o <profile_file>
>>>>>>>> Â Â Â Â Â or
>>>>>>>> Â Â Â Â Â Â Â Â $ create_llvm_prof --binary=<vmlinux> --
>>>>>>>> profile=<perf_file> \
>>>>>>>> Â Â Â Â Â Â Â Â Â Â --format=extbinary --out=<profile_file>
>>>>>>>>
>>>>>>>> Â Â Â Â Â Note that multiple AutoFDO profile files can be merged
>>>>>>>> into one via:
>>>>>>>> Â Â Â Â Â Â Â Â $ llvm-profdata merge -o <profile_file>Â <profile_1> ...
>>>>>>>> <profile_n>
>>>>>>>>
>>>>>>>> 6) Rebuild the kernel using the AutoFDO profile file with the
>>>>>>>> same config
>>>>>>>> Â Â Â Â Â as step 1, (Note CONFIG_AUTOFDO_CLANG needs to be enabled):
>>>>>>>> Â Â Â Â Â Â Â Â $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file>
>>>>>>>>
>>>>>>>> Co-developed-by: Han Shen<shenhan@...gle.com>
>>>>>>>> Signed-off-by: Han Shen<shenhan@...gle.com>
>>>>>>>> Signed-off-by: Rong Xu<xur@...gle.com>
>>>>>>>> Suggested-by: Sriraman Tallam<tmsriram@...gle.com>
>>>>>>>> Suggested-by: Krzysztof Pszeniczny<kpszeniczny@...gle.com>
>>>>>>>> Suggested-by: Nick Desaulniers<ndesaulniers@...gle.com>
>>>>>>>> Suggested-by: Stephane Eranian<eranian@...gle.com>
>>>>>>>> Tested-by: Yonghong Song<yonghong.song@...ux.dev>
>>>>>>>> Tested-by: Yabin Cui<yabinc@...gle.com>
>>>>>>>> Tested-by: Nathan Chancellor<nathan@...nel.org>
>>>>>>>> Reviewed-by: Kees Cook<kees@...nel.org>
>>>>>>> Tested-by: Peter Jung<ptr1337@...hyos.org>
>>>>>>>
>>>>>> The compilations and testing with the "make pacman-pkg" function from
>>>>>> the kernel worked fine.
>>>>>>
>>>>>> One problem I do face:
>>>>>> When I apply a AutoFDO profile together with the PKGBUILD [1] from
>>>>>> archlinux im running into issues at "module_install" at the
>>>>>> packaging.
>>>>>>
>>>>>> See following log:
>>>>>> ```
>>>>>> make[2]: *** [scripts/Makefile.modinst:125:
>>>>>> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-
>>>>>> autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/
>>>>>> arch/x86/kvm/kvm.ko]
>>>>>> Error 1
>>>>>> make[2]: *** Deleting file
>>>>>> '/tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-
>>>>>> autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/
>>>>>> arch/x86/kvm/kvm.ko'
>>>>>> Â Â Â Â INSTALL
>>>>>> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-
>>>>>> autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/
>>>>>> crypto/cryptd.ko
>>>>>> make[2]: *** Waiting for unfinished jobs....
>>>>>> ```
>>>>>>
>>>>>>
>>>>>> This can be fixed with removed "INSTALL_MOD_STRIP=1" to the passed
>>>>>> parameters of module_install.
>>>>>>
>>>>>> This explicitly only happens, if a profile is passed - otherwise the
>>>>>> packaging works without problems.
>>>>>>
>>>>>> Regards,
>>>>>>
>>>>>> Peter Jung
>>>>>>
>
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