From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 44FB5ECDE44 for ; Fri, 19 Oct 2018 12:49:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E0EC72148E for ; Fri, 19 Oct 2018 12:49:33 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="mtTACl8X" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E0EC72148E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727455AbeJSUza (ORCPT ); Fri, 19 Oct 2018 16:55:30 -0400 Received: from mail-pf1-f196.google.com ([209.85.210.196]:45710 "EHLO mail-pf1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727387AbeJSUza (ORCPT ); Fri, 19 Oct 2018 16:55:30 -0400 Received: by mail-pf1-f196.google.com with SMTP id u12-v6so16424699pfn.12; Fri, 19 Oct 2018 05:49:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id; bh=v53VOhpvdqD2goKHpsQ31/M2H7LSlO0Giftj6gqCpzg=; b=mtTACl8X76edZoze9nxR73GDDbGqUyhTRIlLL+bOUR6FPqocBwvlK9ofX9R7+3owJn vBH28NH6R/uCNbRoy5OcO+n1Bd/1mvIycd8OoK4D+ORQLAc+Nxbj7MgBSfPq+Ke0n7wO A4JBXPsdGR+pkGU/zU1jw5m9XMUnhaaiLfLfdOcnCFv5UeifWZs+turyAqRywX0SUA9g KlNdl3cYTzMgoGX3jUnCMYc3/OtZxATo3Z9SK0nDbdcKu3oJE3zrm+lFaufAgG53YF4b RSr6fRGiVVwjSd8zMyqa927bdkvs6jMK2VrRqgdU7veVqDTSVZ9W/ng7Vj+fk6X3tUHb BF5Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id; bh=v53VOhpvdqD2goKHpsQ31/M2H7LSlO0Giftj6gqCpzg=; b=IM/Phuulid1rD+kd9nFCraWF141mJ7vVaBG0ekvrHmxRcvx2Uc2SLoI7A6WHjkJYa4 BwVakXM4QDFKGttHFg2ZDR5Fo1QL7n0Kacl+gZ9eAJnxuZt14SKZT9GaAcQR87DxxFDN ah+veCRK+1gzT8i5GRFZxDV5RExgRHrH3h4P2sNmdulQ6z42QXU5apvpVJWu6VAfcrvW x5A7ECxlLG9vi9ZzO/wyoyZM+IrdEvbSN89hoE/0MT+IteiXsPKXEPTWsC41hI8qhMQA 54brCnEY9+cBo0AdOceZxHdpmZrwsad9EbCddWZvymsUmjIyBE2KwdgoHLFFBamvqzRw YUfg== X-Gm-Message-State: ABuFfogg/nUjdBzgihBfWCa/qISa/tI+MGvmCEXkPuzgSSxgRKqhpCfn 6sFDUdbYlNiNCSEANX7k2/s= X-Google-Smtp-Source: ACcGV62GrHLHqWuXwacnk9262+wvFsfGTCyUKFAgk/7+W+wpnMFkpyhD6XDhJJELjm4BkOn7xId0hA== X-Received: by 2002:a63:4384:: with SMTP id q126-v6mr32510375pga.142.1539953371467; Fri, 19 Oct 2018 05:49:31 -0700 (PDT) Received: from vultr.guest ([2001:19f0:6001:4ff6:5400:1ff:feb7:a195]) by smtp.gmail.com with ESMTPSA id o131-v6sm33640679pgo.53.2018.10.19.05.49.30 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 19 Oct 2018 05:49:30 -0700 (PDT) From: Du Changbin To: yamada.masahiro@socionext.com, michal.lkml@markovi.net, tglx@linutronix.de, mingo@redhat.com, linux@armlinux.org.uk, akpm@linux-foundation.org Cc: rostedt@goodmis.org, x86@kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-sparse@vger.kernel.org, robin.murphy@arm.com, Du Changbin Subject: [PATCH v2 0/4] kernel hacking: GCC optimization for better debug experience (-Og) Date: Fri, 19 Oct 2018 12:49:17 +0000 Message-Id: <20181019124921.13780-1-changbin.du@gmail.com> X-Mailer: git-send-email 2.17.1 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi all, I have posted this series several months ago but interrupted by personal affairs. Now I get time to complete this task. Thanks for all of the reviewers. I know some kernel developers was searching for a method to dissable GCC optimizations, probably they want to apply GCC '-O0' option. But since Linux kernel relies on GCC optimization to remove some dead code, so '-O0' just breaks the build. They do need this because they want to debug kernel with qemu, simics, kgtp or kgdb. Thanks for the GCC '-Og' optimization level introduced in GCC 4.8, which offers a reasonable level of optimization while maintaining fast compilation and a good debugging experience. It is similar to '-O1' while perferring to keep debug ability over runtime speed. With '-Og', we can build a kernel with better debug ability and little performance drop after some simple change. In this series, firstly introduce a new config CONFIG_NO_AUTO_INLINE after two fixes for this new option. With this option, only functions explicitly marked with "inline" will be inlined. This will allow the function tracer to trace more functions because it only traces functions that the compiler has not inlined. Then introduce new config CC_OPTIMIZE_FOR_DEBUGGING which apply '-Og' optimization level for whole kernel, with a simple fix in fix_to_virt(). Currently I have only tested this option on x86 and ARM platform. Other platforms should also work but probably need some compiling fixes as what having done in this series. I leave that to who want to try this debug option. Comparison of vmlinux size: a bit smaller. w/o CONFIG_CC_OPTIMIZE_FOR_DEBUGGING $ size vmlinux text data bss dec hex filename 22665554 9709674 2920908 35296136 21a9388 vmlinux w/ CONFIG_CC_OPTIMIZE_FOR_DEBUGGING $ size vmlinux text data bss dec hex filename 21499032 10102758 2920908 34522698 20ec64a vmlinux Comparison of system performance: a bit drop (~6%). This benchmark of kernel compilation is suggested by Ingo Molnar. https://lkml.org/lkml/2018/5/2/74 Preparation: Set cpufreq to 'performance'. for ((cpu=0; cpu<120; cpu++)); do G=/sys/devices/system/cpu/cpu$cpu/cpufreq/scaling_governor [ -f $G ] && echo performance > $G done w/o CONFIG_CC_OPTIMIZE_FOR_DEBUGGING $ perf stat --repeat 5 --null --pre '\ cp -a kernel ../kernel.copy.$(date +%s); \ rm -rf *; \ git checkout .; \ echo 1 > /proc/sys/vm/drop_caches; \ find ../kernel* -type f | xargs cat >/dev/null; \ make -j kernel >/dev/null; \ make clean >/dev/null 2>&1; \ sync '\ \ make -j8 >/dev/null Performance counter stats for 'make -j8' (5 runs): 219.764246652 seconds time elapsed ( +- 0.78% ) w/ CONFIG_CC_OPTIMIZE_FOR_DEBUGGING $ perf stat --repeat 5 --null --pre '\ cp -a kernel ../kernel.copy.$(date +%s); \ rm -rf *; \ git checkout .; \ echo 1 > /proc/sys/vm/drop_caches; \ find ../kernel* -type f | xargs cat >/dev/null; \ make -j kernel >/dev/null; \ make clean >/dev/null 2>&1; \ sync '\ \ make -j8 >/dev/null Performance counter stats for 'make -j8' (5 runs): 233.574187771 seconds time elapsed ( +- 0.19% ) Du Changbin (4): x86/mm: surround level4_kernel_pgt with #ifdef CONFIG_X86_5LEVEL...#endif kernel hacking: new config NO_AUTO_INLINE to disable compiler auto-inline optimizations ARM: mm: fix build error in fix_to_virt with CONFIG_CC_OPTIMIZE_FOR_DEBUGGING kernel hacking: new config CC_OPTIMIZE_FOR_DEBUGGING to apply GCC -Og optimization Makefile | 11 +++++++++++ arch/arm/mm/mmu.c | 2 +- arch/x86/include/asm/pgtable_64.h | 2 ++ arch/x86/kernel/head64.c | 13 ++++++------- include/linux/compiler-gcc.h | 2 +- include/linux/compiler.h | 2 +- init/Kconfig | 19 +++++++++++++++++++ lib/Kconfig.debug | 17 +++++++++++++++++ 8 files changed, 58 insertions(+), 10 deletions(-) -- 2.17.1