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=-12.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 06F90C48BD1 for ; Thu, 10 Jun 2021 18:54:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D9E3D613FF for ; Thu, 10 Jun 2021 18:54:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230401AbhFJS4t (ORCPT ); Thu, 10 Jun 2021 14:56:49 -0400 Received: from mail.kernel.org ([198.145.29.99]:50170 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229935AbhFJS4r (ORCPT ); Thu, 10 Jun 2021 14:56:47 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 6C399613B0; Thu, 10 Jun 2021 18:54:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1623351290; bh=UgDy/YIt0wcpF3ZFwRGLuTVpW0LrD/15mzM1MbySke0=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=UVcjrF6tcIWAwppxNnC9vo54gFl1xDCWWPPdU+nAG9e76MrBYDxIm8NtmJgvu2o8f 4aCh5Dd7Qbbrw6LnWSrcqXxlzga8tCfsVxodq4mX4rD3/lCRUwIm1NDKQZGfZf6aPo +ySG5os3M0Pm88ldw+khux3FgUFGfEmlLjEqNOuO3V4sursnspIM9yDAkDDguLl70V Y4LCnWliy4i0+mPqLglSbDhZxGIeORHh8sBJ8W1heMFyt2VX+WMVHO6Xmj6nWrzFqg J/RTBZJP36ppI1QeGgWiDk5dK4NYqJ2j0LFoGvwyD1DRkzhHmuFWkwGJFr6Lrqwp0S WYdvFpnL1933Q== Subject: Re: [PATCH 01/13] objtool: Rewrite hashtable sizing To: Peter Zijlstra Cc: x86@kernel.org, jpoimboe@redhat.com, jbaron@akamai.com, rostedt@goodmis.org, ardb@kernel.org, linux-kernel@vger.kernel.org, samitolvanen@google.com, ndesaulniers@google.com, clang-built-linux@googlegroups.com References: <20210506193352.719596001@infradead.org> <20210506194157.452881700@infradead.org> From: Nathan Chancellor Message-ID: <7165b24e-0628-c273-f1e2-67a75358991f@kernel.org> Date: Thu, 10 Jun 2021 11:54:50 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/10/2021 11:43 AM, Peter Zijlstra wrote: > On Thu, Jun 10, 2021 at 11:14:51AM -0700, Nathan Chancellor wrote: > >> This patch as commit 25cf0d8aa2a3 ("objtool: Rewrite hashtable sizing") >> in -tip causes a massive compile time regression with allmodconfig + >> ThinLTO. > > Moo... the allyesconfig builds I used it on were much faster, but that > was on regular GCC vmlinux.o after linking. > >> Adding Sami because I am not sure why this patch would have much of an impact >> in relation to LTO. https://git.kernel.org/tip/25cf0d8aa2a3 is the patch in >> question. >> >> If I can provide any further information or help debug, please let me know. >> >> If you are interested in reproducing this locally, you will need a >> fairly recent LLVM stack (I used the stable release/12.x branch) and to >> cherry-pick commit 976aac5f8829 ("kcsan: Fix debugfs initcall return >> type") to fix an unrelated build failure. My script [2] can build a >> self-contained toolchain fairly quickly if you cannot get one from your >> package manager. A command like below will speed up the build a bit: > > Would something like llvm-13 from Debian be good enough? > > $ clang-13 --version > Debian clang version 13.0.0-++20210418105309+a0898f0cecc7-1~exp1 > Target: x86_64-pc-linux-gnu > Thread model: posix > InstalledDir: /usr/bin > Yes, that would work. That is what we use in our CI. Looks like Sami gave a reply that explains it. Cheers, Nathan