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=-5.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 30109C433E9 for ; Wed, 10 Mar 2021 20:22:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 00A5564FDD for ; Wed, 10 Mar 2021 20:22:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231627AbhCJUWO (ORCPT ); Wed, 10 Mar 2021 15:22:14 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51726 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231668AbhCJUVy (ORCPT ); Wed, 10 Mar 2021 15:21:54 -0500 Received: from mail-il1-x135.google.com (mail-il1-x135.google.com [IPv6:2607:f8b0:4864:20::135]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D1390C061756 for ; Wed, 10 Mar 2021 12:21:53 -0800 (PST) Received: by mail-il1-x135.google.com with SMTP id r7so1175728ilb.0 for ; Wed, 10 Mar 2021 12:21:53 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=16SMPeE21CushitzJ7QMJXGi9ZvpBG0rD0GsXsI6hkU=; b=spJ0UNdk80g6IuuuMgwcY1AR/MlQcbuEaGPdCTXj/1jApxV2p8lLCbpw2FXeZARvWw y/3ktMyTJ21jResBV0RdchCy0MqpQWNv6dER4WFlnhzYk11bwv9aqcm+KgHMLqKIFAg9 wF9GAaMI7rlW6A9bWBqHeVNEog/S6909mlwkSYh4TiTs7CPTx7DyMRuCfR5rgcfLGNPw 7niYk993aUFxdD50MZMH/zMHbKSz3aFLl/hTPoGJ9DZoAjDfDnhpA9Yejl0H8WuBPrrr mEbiTH3WB8Tk5vq0oyUEyB0M7QqkyfIHA/kpU0TP4QB2m7ME4eNl4B6QEjUSfovzkZcb hE7w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=16SMPeE21CushitzJ7QMJXGi9ZvpBG0rD0GsXsI6hkU=; b=toypPmm8URCm7Lq4GCDhZd2FCQGJdVXNuiPU45IffE9Hww24vTUm5i8VYdoISr+kl4 Cz3Ckm0H0PcsS//woX6R+5kILUKcNxur5ZRvYoOarb6fDeen53P9LnyYTGeFAr851L99 ZwUocuQQj9MPqU4LhUEB39ApipDSNanTKyXXxtfDQHjdrLmupC0IX/ZRuS53SLEN0GwK 5/v+LTU1ns4JR20YjIyjPukQvrRojRTsNDokzReiUq0mFb+Zndt6mx+XWc3ru057o3cz X3072Mkkuj1Ide1paZMGQeUG6+bQuRiViTqeIi07oY4KctYk7A+mn9/EHpzev8A/xK18 +vcA== X-Gm-Message-State: AOAM532Q6a5RraxAEN80bdFLxC/t9lSdp7pna+rEr0R63xk9UDNei0ce p4PHz50BKCwYyJ2EGN5sVqQ0Sg== X-Google-Smtp-Source: ABdhPJzg7g/La5YMg5wKnM0/F2ii9+d2ML0g09VHJPp0z1r9WLx+9Fj1ToRDzy/DzFD7axi1WAT7xQ== X-Received: by 2002:a92:1312:: with SMTP id 18mr3843559ilt.92.1615407713037; Wed, 10 Mar 2021 12:21:53 -0800 (PST) Received: from [192.168.1.30] ([65.144.74.34]) by smtp.gmail.com with ESMTPSA id h15sm199377ils.73.2021.03.10.12.21.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 10 Mar 2021 12:21:52 -0800 (PST) Subject: Re: -Walign-mismatch in block/blk-mq.c To: Nathan Chancellor Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com References: <20210310182307.zzcbi5w5jrmveld4@archlinux-ax161> From: Jens Axboe Message-ID: <99cf90ea-81c0-e110-4815-dd1f7df36cb4@kernel.dk> Date: Wed, 10 Mar 2021 13:21:52 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210310182307.zzcbi5w5jrmveld4@archlinux-ax161> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/10/21 11:23 AM, Nathan Chancellor wrote: > Hi Jens, > > There is a new clang warning added in the development branch, > -Walign-mismatch, which shows an instance in block/blk-mq.c: > > block/blk-mq.c:630:39: warning: passing 8-byte aligned argument to > 32-byte aligned parameter 2 of 'smp_call_function_single_async' may > result in an unaligned pointer access [-Walign-mismatch] > smp_call_function_single_async(cpu, &rq->csd); > ^ > 1 warning generated. > > There appears to be some history here as I can see that this member was > purposefully unaligned in commit 4ccafe032005 ("block: unalign > call_single_data in struct request"). However, I later see a change in > commit 7c3fb70f0341 ("block: rearrange a few request fields for better > cache layout") that seems somewhat related. Is it possible to get back > the alignment by rearranging the structure again? This seems to be the > only solution for the warning aside from just outright disabling it, > which would be a shame since it seems like it could be useful for > architectures that cannot handle unaligned accesses well, unless I am > missing something obvious :) It should not be hard to ensure that alignment without re-introducing the bloat. Is there some background on why 32-byte alignment is required? -- Jens Axboe