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 83F79146592; Tue, 25 Jun 2024 10:01:05 +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=1719309665; cv=none; b=GjcU7ddC2hd76zEHr46cX2ngaNPmDgRPgJH7vovv7loWks7N1L9LqxJHcoGvPC3JGCP2tDVL0PanDpYs6/Hj0jc4MSHDYXAvffA+d+XS6+wgT8QcPCYvf5A+R0JqspSSZX1Rjs0N0XhtgmaJYOiKdqejrKN53SxZfaTzJxX38cs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719309665; c=relaxed/simple; bh=hvMefsArZr2n6/8VY7c1ww2UCMv05epW7BGs4b063uU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=oDfds1Smb+Iu15c4OOAAnXa/GjQ6W1czhJMxAVl7YP7tCI7TgaL2MQE/ntQ84KDUOJBuGALdOp78AFjn8iCD88k4oud787k9x/VPlOtSG4enjIuXclY80DSh5p+tBa4WjmVg5oiL9jlcTdUVxSmBcS8ecVV7OTxyW50Ogzli7i4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=mvW60j3A; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="mvW60j3A" Received: by smtp.kernel.org (Postfix) with ESMTPSA id ABDB7C32781; Tue, 25 Jun 2024 10:01:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1719309665; bh=hvMefsArZr2n6/8VY7c1ww2UCMv05epW7BGs4b063uU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=mvW60j3AK00N2BPilo65HUPL8NVEMwEH4Zj4q4uCFr2TuIPbZ/0YacR+HDvosw7Bo EHLo7tr71R1Xl6moYshOwxPwdobjUamNTyhOuwjkLsAm3ecjcU/JMPFGFOh51W0pRZ xxBH5RyVcIifxPpeDRfCer0taeRl9H/h9gY46EUw= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Yifan Hong , Masami Hiramatsu , Nathan Chancellor , Masahiro Yamada Subject: [PATCH 6.1 092/131] kbuild: Remove support for Clangs ThinLTO caching Date: Tue, 25 Jun 2024 11:34:07 +0200 Message-ID: <20240625085529.434835195@linuxfoundation.org> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20240625085525.931079317@linuxfoundation.org> References: <20240625085525.931079317@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Nathan Chancellor commit aba091547ef6159d52471f42a3ef531b7b660ed8 upstream. There is an issue in clang's ThinLTO caching (enabled for the kernel via '--thinlto-cache-dir') with .incbin, which the kernel occasionally uses to include data within the kernel, such as the .config file for /proc/config.gz. For example, when changing the .config and rebuilding vmlinux, the copy of .config in vmlinux does not match the copy of .config in the build folder: $ echo 'CONFIG_LTO_NONE=n CONFIG_LTO_CLANG_THIN=y CONFIG_IKCONFIG=y CONFIG_HEADERS_INSTALL=y' >kernel/configs/repro.config $ make -skj"$(nproc)" ARCH=x86_64 LLVM=1 clean defconfig repro.config vmlinux ... $ grep CONFIG_HEADERS_INSTALL .config CONFIG_HEADERS_INSTALL=y $ scripts/extract-ikconfig vmlinux | grep CONFIG_HEADERS_INSTALL CONFIG_HEADERS_INSTALL=y $ scripts/config -d HEADERS_INSTALL $ make -kj"$(nproc)" ARCH=x86_64 LLVM=1 vmlinux ... UPD kernel/config_data GZIP kernel/config_data.gz CC kernel/configs.o ... LD vmlinux ... $ grep CONFIG_HEADERS_INSTALL .config # CONFIG_HEADERS_INSTALL is not set $ scripts/extract-ikconfig vmlinux | grep CONFIG_HEADERS_INSTALL CONFIG_HEADERS_INSTALL=y Without '--thinlto-cache-dir' or when using full LTO, this issue does not occur. Benchmarking incremental builds on a few different machines with and without the cache shows a 20% increase in incremental build time without the cache when measured by touching init/main.c and running 'make all'. ARCH=arm64 defconfig + CONFIG_LTO_CLANG_THIN=y on an arm64 host: Benchmark 1: With ThinLTO cache Time (mean ± σ): 56.347 s ± 0.163 s [User: 83.768 s, System: 24.661 s] Range (min … max): 56.109 s … 56.594 s 10 runs Benchmark 2: Without ThinLTO cache Time (mean ± σ): 67.740 s ± 0.479 s [User: 718.458 s, System: 31.797 s] Range (min … max): 67.059 s … 68.556 s 10 runs Summary With ThinLTO cache ran 1.20 ± 0.01 times faster than Without ThinLTO cache ARCH=x86_64 defconfig + CONFIG_LTO_CLANG_THIN=y on an x86_64 host: Benchmark 1: With ThinLTO cache Time (mean ± σ): 85.772 s ± 0.252 s [User: 91.505 s, System: 8.408 s] Range (min … max): 85.447 s … 86.244 s 10 runs Benchmark 2: Without ThinLTO cache Time (mean ± σ): 103.833 s ± 0.288 s [User: 232.058 s, System: 8.569 s] Range (min … max): 103.286 s … 104.124 s 10 runs Summary With ThinLTO cache ran 1.21 ± 0.00 times faster than Without ThinLTO cache While it is unfortunate to take this performance improvement off the table, correctness is more important. If/when this is fixed in LLVM, it can potentially be brought back in a conditional manner. Alternatively, a developer can just disable LTO if doing incremental compiles quickly is important, as a full compile cycle can still take over a minute even with the cache and it is unlikely that LTO will result in functional differences for a kernel change. Cc: stable@vger.kernel.org Fixes: dc5723b02e52 ("kbuild: add support for Clang LTO") Reported-by: Yifan Hong Closes: https://github.com/ClangBuiltLinux/linux/issues/2021 Reported-by: Masami Hiramatsu Closes: https://lore.kernel.org/r/20220327115526.cc4b0ff55fc53c97683c3e4d@kernel.org/ Signed-off-by: Nathan Chancellor Signed-off-by: Masahiro Yamada [nathan: Address conflict in Makefile] Signed-off-by: Nathan Chancellor Signed-off-by: Greg Kroah-Hartman --- Makefile | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) --- a/Makefile +++ b/Makefile @@ -980,7 +980,6 @@ endif ifdef CONFIG_LTO_CLANG ifdef CONFIG_LTO_CLANG_THIN CC_FLAGS_LTO := -flto=thin -fsplit-lto-unit -KBUILD_LDFLAGS += --thinlto-cache-dir=$(extmod_prefix).thinlto-cache else CC_FLAGS_LTO := -flto endif @@ -1588,7 +1587,7 @@ endif # CONFIG_MODULES # Directories & files removed with 'make clean' CLEAN_FILES += include/ksym vmlinux.symvers modules-only.symvers \ modules.builtin modules.builtin.modinfo modules.nsdeps \ - compile_commands.json .thinlto-cache rust/test rust/doc \ + compile_commands.json rust/test rust/doc \ .vmlinux.objs .vmlinux.export.c # Directories & files removed with 'make mrproper' @@ -1884,7 +1883,7 @@ PHONY += compile_commands.json clean-dirs := $(KBUILD_EXTMOD) clean: rm-files := $(KBUILD_EXTMOD)/Module.symvers $(KBUILD_EXTMOD)/modules.nsdeps \ - $(KBUILD_EXTMOD)/compile_commands.json $(KBUILD_EXTMOD)/.thinlto-cache + $(KBUILD_EXTMOD)/compile_commands.json PHONY += prepare # now expand this into a simple variable to reduce the cost of shell evaluations