From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BE19D79F6; Sun, 20 Oct 2024 15:46:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729439180; cv=none; b=trKUMTswItE6W+k7JMGOxJoIKaPEwY6tKgdjsXIvTc/T6u8kh4BvSrC3r6lojRus7KtYlBntgX+Hf/OkM9rjFnp7pgk8jhf2ssYodRQSgboFfu55ZO/pEp20GpeYCkCJOy+7NUyQ8UXgyQFIJL1KTKtJy3cI0XBs1ShLsa5iJMQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729439180; c=relaxed/simple; bh=dybJvTIwydrLBvn1LcH/lZMry79zGiff5879XyIL0zg=; h=MIME-Version:References:In-Reply-To:From:Date:Message-ID:Subject: To:Cc:Content-Type; b=KBYHnYFZQ/Bl2Ap7H+NuHFvLNDwccswBBdmoTRdjKxJGopIpM7CYSr8sPT/l+UjE4Dry5zkJR68G/w05aVpTutvsOLotaWhHlMqPha45RtmfxM4yY6oEuXkXsNF+WZXze2zZ3M+Vyq7v+XVTukghjwILFLy5qUO7AjbNPl4kV8w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=N6++6gGR; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="N6++6gGR" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2FA70C4CEED; Sun, 20 Oct 2024 15:46:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1729439179; bh=dybJvTIwydrLBvn1LcH/lZMry79zGiff5879XyIL0zg=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=N6++6gGRhYbOmKLkI0kMy8uxf1eJcK4QpzjTYHkL31hos9eglTtkadQEkZ/MKD9dr ODlp6brmU1BX7rahC8gGEnmNg+jtDeRSCKCdP8dPebFk5KdKlGZwNjW1ZYaJeKawvv dF3os4hhX8qDXh7kWjUaSVAE1tb9Frd/A3tjy4/H/eeHmhimSXVYCkMjgpLTkoooOz ZA3oYHjAEQeeUNiW2Ebyo0Sd0U0V3dALSCYWKi3K4KRTt9S0MWh+NlfZP+S9IE2k+D +RSFLyDtX8+SHqh6ElD5KtbS/b3eSO0EFV7XavmYBCAQrUyfvItQn4Cca1G4JqbmFG qdwFQn4fVrI7g== Received: by mail-lf1-f46.google.com with SMTP id 2adb3069b0e04-539e5c15fd3so3196283e87.3; Sun, 20 Oct 2024 08:46:19 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCUGqjOS0ZBono+H6G90YZ8lfFT0rfaOD4hKJS1dInh2Y3K/cfuMQ4pbktHkRaCQLWwrVvYC/4s7BMAL@vger.kernel.org, AJvYcCUfNeWToORR91pyjPvKlTBjxXuLZO9wC9YZLD4sbe3WQRfNJx5guZ2mkPnBR9j3JvX29W1P/rvUs77A@vger.kernel.org, AJvYcCWRIhObuqR5VCoDaAzXWXFbUbU+XI/1sGYqOy3w8NCxo72mxdYJNMtL9CuShM92HXBxrPwsgHcvlNxg@vger.kernel.org, AJvYcCXeXflE1soAtFmC4VSENPnCscf4Zfqdkh1JY9rkunotMvAKPtfPLxw76jQDROFzNYJ8omDoobUJ4moGwIgd@vger.kernel.org, AJvYcCXrsEES+YuvMDJnJqr+YdHB5suz9UvgBKHGL0X617M8QaJkJdIZ2L3kdzZe0/8kgqVyj2TMmEMwCFbLE8hc@vger.kernel.org X-Gm-Message-State: AOJu0Yws/O1VzMEbCyzlFG4/VB1RO3z4+mBlGOnjtdKFGvGi+qpBTCmT 4Wv+LFDMiLpH+DPK6Av+W8rbvczASBnFUkRLFFGbh/EL3i2IVMgf5ISPSvh5fFfEyREhRRqFXWs NZZm8WW0y7b6tzURCKnF529YZhdM= X-Google-Smtp-Source: AGHT+IHVNEBd41mpXJ65nn09YsbsLIWj9/J956BaHSIAk6ZWD5G3zkZ2X2eav8p4dtbyv45AK6HMs6lPUuxyTCIJaXo= X-Received: by 2002:a05:6512:104a:b0:539:e0fa:6ee8 with SMTP id 2adb3069b0e04-53a1520b6a6mr4932543e87.6.1729439177507; Sun, 20 Oct 2024 08:46:17 -0700 (PDT) Precedence: bulk X-Mailing-List: workflows@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20241014213342.1480681-1-xur@google.com> <20241020033116.GA3653827@thelio-3990X> In-Reply-To: <20241020033116.GA3653827@thelio-3990X> From: Masahiro Yamada Date: Mon, 21 Oct 2024 00:45:40 +0900 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v4 0/6] Add AutoFDO and Propeller support for Clang build To: Nathan Chancellor Cc: Rong Xu , Andrew Morton , Alice Ryhl , Arnd Bergmann , Bill Wendling , Borislav Petkov , Breno Leitao , Brian Gerst , Dave Hansen , David Li , Han Shen , Heiko Carstens , "H. Peter Anvin" , Ingo Molnar , Jann Horn , Jonathan Corbet , Josh Poimboeuf , Juergen Gross , Justin Stitt , Kees Cook , "Mike Rapoport (IBM)" , Nick Desaulniers , Nicolas Schier , "Paul E. McKenney" , Peter Zijlstra , Sami Tolvanen , Thomas Gleixner , Wei Yang , workflows@vger.kernel.org, Miguel Ojeda , Maksim Panchenko , x86@kernel.org, linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Sun, Oct 20, 2024 at 12:31=E2=80=AFPM Nathan Chancellor wrote: > > Hi Masahiro and Andrew, > > Top posting only for visibility. Would it make more sense to have this > land via the Kbuild tree or -mm? The core of the series really touches > Kbuild and I think the x86 stuff can just land with Acks, unless the > -tip folks feel differently. I would like Rong to have a relatively > clear path forward to mainline once the requisite review and testing has > accomplished, which requires a shepherd :) I think I can pick it up if 2/6 gains Ack from an objtool maintainer. > Cheers, > Nathan > > On Mon, Oct 14, 2024 at 02:33:34PM -0700, Rong Xu wrote: > > Hi, > > > > This patch series is to integrate AutoFDO and Propeller support into > > the Linux kernel. AutoFDO is a profile-guided optimization technique > > that leverages hardware sampling to enhance binary performance. > > Unlike Instrumentation-based FDO (iFDO), AutoFDO offers a user-friendly > > and straightforward application process. While iFDO generally yields > > superior profile quality and performance, our findings reveal that > > AutoFDO achieves remarkable effectiveness, bringing performance close > > to iFDO for benchmark applications. > > > > Propeller is a profile-guided, post-link optimizer that improves > > the performance of large-scale applications compiled with LLVM. It > > operates by relinking the binary based on an additional round of runtim= e > > profiles, enabling precise optimizations that are not possible at > > compile time. Similar to AutoFDO, Propeller too utilizes hardware > > sampling to collect profiles and apply post-link optimizations to impro= ve > > the benchmark=E2=80=99s performance over and above AutoFDO. > > > > Our empirical data demonstrates significant performance improvements > > with AutoFDO and Propeller, up to 10% on microbenchmarks and up to 5% > > on large warehouse-scale benchmarks. This makes a strong case for their > > inclusion as supported features in the upstream kernel. > > > > Background > > > > A significant fraction of fleet processing cycles (excluding idle time) > > from data center workloads are attributable to the kernel. Ware-house > > scale workloads maximize performance by optimizing the production kerne= l > > using iFDO (a.k.a instrumented PGO, Profile Guided Optimization). > > > > iFDO can significantly enhance application performance but its use > > within the kernel has raised concerns. AutoFDO is a variant of FDO that > > uses the hardware=E2=80=99s Performance Monitoring Unit (PMU) to collec= t > > profiling data. While AutoFDO typically yields smaller performance > > gains than iFDO, it presents unique benefits for optimizing kernels. > > > > AutoFDO eliminates the need for instrumented kernels, allowing a single > > optimized kernel to serve both execution and profile collection. It als= o > > minimizes slowdown during profile collection, potentially yielding > > higher-fidelity profiling, especially for time-sensitive code, compared > > to iFDO. Additionally, AutoFDO profiles can be obtained from production > > environments via the hardware=E2=80=99s PMU whereas iFDO profiles requi= re > > carefully curated load tests that are representative of real-world > > traffic. > > > > AutoFDO facilitates profile collection across diverse targets. > > Preliminary studies indicate significant variation in kernel hot spots > > within Google=E2=80=99s infrastructure, suggesting potential performanc= e gains > > through target-specific kernel customization. > > > > Furthermore, other advanced compiler optimization techniques, including > > ThinLTO and Propeller can be stacked on top of AutoFDO, similar to iFDO= . > > ThinLTO achieves better runtime performance through whole-program > > analysis and cross module optimizations. The main difference between > > traditional LTO and ThinLTO is that the latter is scalable in time and > > memory. > > > > This patch series adds AutoFDO and Propeller support to the kernel. The > > actual solution comes in six parts: > > > > [P 1] Add the build support for using AutoFDO in Clang > > > > Add the basic support for AutoFDO build and provide the > > instructions for using AutoFDO. > > > > [P 2] Fix objtool for bogus warnings when -ffunction-sections is enable= d > > > > [P 3] Change the subsection ordering when -ffunction-sections is enable= d > > > > [P 4] Enable =E2=80=93ffunction-sections for the AutoFDO build > > > > [P 5] Enable Machine Function Split (MFS) optimization for AutoFDO > > > > [P 6] Add Propeller configuration to the kernel build > > > > Patch 1 provides basic AutoFDO build support. Patches 2 to 5 further > > enhance the performance of AutoFDO builds and are functionally dependen= t > > on Patch 1. Patch 6 enables support for Propeller and is dependent on > > patch 2 and patch 3. > > > > Caveats > > > > AutoFDO is compatible with both GCC and Clang, but the patches in this > > series are exclusively applicable to LLVM 17 or newer for AutoFDO and > > LLVM 19 or newer for Propeller. For profile conversion, two different > > tools could be used, llvm_profgen or create_llvm_prof. llvm_profgen > > needs to be the LLVM 19 or newer, or just the LLVM trunk. Alternatively= , > > create_llvm_prof v0.30.1 or newer can be used instead of llvm-profgen. > > > > Additionally, the build is only supported on x86 platforms equipped > > with PMU capabilities, such as LBR on Intel machines. More > > specifically: > > * Intel platforms: works on every platform that supports LBR; > > we have tested on Skylake. > > * AMD platforms: tested on AMD Zen3 with the BRS feature. The kernel > > needs to be configured with =E2=80=9CCONFIG_PERF_EVENTS_AMD_BRS=3Dy"= , To > > check, use > > $ cat /proc/cpuinfo | grep =E2=80=9C brs=E2=80=9D > > For the AMD Zen4, AMD LBRV2 is supported, but we suspect a bug with > > AMD LBRv2 implementation in Genoa which blocks the usage. > > > > Experiments and Results > > > > Experiments were conducted to compare the performance of AutoFDO-optimi= zed > > kernel images (version 6.9.x) against default builds.. The evaluation > > encompassed both open source microbenchmarks and real-world production > > services from Google and Meta. The selected microbenchmarks included Ne= per, > > a network subsystem benchmark, and UnixBench which is a comprehensive s= uite > > for assessing various kernel operations. > > > > For Neper, AutoFDO optimization resulted in a 6.1% increase in throughp= ut > > and a 10.6% reduction in latency. Unixbench saw a 2.2% improvement in i= ts > > index score under low system load and a 2.6% improvement under high sys= tem > > load. > > > > For further details on the improvements observed in Google and Meta's > > production services, please refer to the LLVM discourse post: > > https://discourse.llvm.org/t/optimizing-the-linux-kernel-with-autofdo-i= ncluding-thinlto-and-propeller/79108 > ... > > Rong Xu (6): > > Add AutoFDO support for Clang build > > objtool: Fix unreachable instruction warnings for weak funcitons > > Change the symbols order when --ffuntion-sections is enabled > > AutoFDO: Enable -ffunction-sections for the AutoFDO build > > AutoFDO: Enable machine function split optimization for AutoFDO > > Add Propeller configuration for kernel build. > > > > Documentation/dev-tools/autofdo.rst | 165 ++++++++++++++++++++++++++ > > Documentation/dev-tools/index.rst | 2 + > > Documentation/dev-tools/propeller.rst | 161 +++++++++++++++++++++++++ > > MAINTAINERS | 14 +++ > > Makefile | 2 + > > arch/Kconfig | 42 +++++++ > > arch/x86/Kconfig | 2 + > > arch/x86/kernel/vmlinux.lds.S | 4 + > > include/asm-generic/vmlinux.lds.h | 54 +++++++-- > > scripts/Makefile.autofdo | 25 ++++ > > scripts/Makefile.lib | 20 ++++ > > scripts/Makefile.propeller | 28 +++++ > > tools/objtool/check.c | 2 + > > tools/objtool/elf.c | 15 ++- > > 14 files changed, 524 insertions(+), 12 deletions(-) > > create mode 100644 Documentation/dev-tools/autofdo.rst > > create mode 100644 Documentation/dev-tools/propeller.rst > > create mode 100644 scripts/Makefile.autofdo > > create mode 100644 scripts/Makefile.propeller > > > > > > base-commit: eb952c47d154ba2aac794b99c66c3c45eb4cc4ec > > -- > > 2.47.0.rc1.288.g06298d1525-goog > > -- Best Regards Masahiro Yamada