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=-2.2 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 97C7CC432C0 for ; Tue, 3 Dec 2019 14:37:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6F4B420661 for ; Tue, 3 Dec 2019 14:37:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=kernel-dk.20150623.gappssmtp.com header.i=@kernel-dk.20150623.gappssmtp.com header.b="a35jPxts" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726766AbfLCOhJ (ORCPT ); Tue, 3 Dec 2019 09:37:09 -0500 Received: from mail-io1-f66.google.com ([209.85.166.66]:42462 "EHLO mail-io1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725957AbfLCOhJ (ORCPT ); Tue, 3 Dec 2019 09:37:09 -0500 Received: by mail-io1-f66.google.com with SMTP id f82so3919469ioa.9 for ; Tue, 03 Dec 2019 06:37:07 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:to:references:from:message-id:date:user-agent:mime-version :in-reply-to:content-language:content-transfer-encoding; bh=qGRbXUbqd8Z04mtkdXBEuHQg2LkRCVP7LlXsnOJdoYc=; b=a35jPxtshV8+pMg3W3CCCGSqlVGoB1OuQXVQZIKX5SfRQ/C6xoX3NgNI/KLPHUoz/+ frqVxdDd3L1rWzUg9Xsl4MbHtvgc6ts2mfVf38VPaGTBbusI4xrxHkxAP9kEjVCE9Q/3 nB/uItPGJVSLLETsjYO6iTi3UZrVPnFYzSG3iqJM7/qgb/lBYdm6DrrT79c14qRz7KC5 bolEx/oZAaESAAVP91g8jC6gLJUfJF0JK7Z2Y1U25ThPi7atVlWTVFy8//i68yx/LZAH lCYEYn689f9WMK4hWVOQd/T4l7AcCjc8/BNr4inDpiUYCmTijK2PQ3Z9KiyscdgoI/bk IiIg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=qGRbXUbqd8Z04mtkdXBEuHQg2LkRCVP7LlXsnOJdoYc=; b=uRWu1o6Rwfec/40MGO/Td2ESmW4zb5P3RwiiA/VZoQ3comhMjFrVNEdDOYDEEzs1HE dLPGPtEp66HMk0Es9bcU1WKESOWgsDYes+L0awWtRIhsCgiemApTYg4E6ZWPWlP/301V G3G9bKIQZuJ+cF1JrBly3jk6NS1l/ezTHOpv4yjU/Ne5txH2a+NBxPSneiFG3s4Rf2XC IzVNqyiX/pBZOO0vGUGxAzhUqkSZkcOvVoLYrAAJNgAGvcgJOhZ9XvS5ra+O58NuXzdX Qmh/gPCjA2VyYrrH4hF4FixjaZH9ijolt0BT8g3qx8dSh4WFBBQRcHDG7lwGi1cRpj+I iIYA== X-Gm-Message-State: APjAAAUr3hSUxCcpbpavQw0cSjsER/rAvMNd/iPyJUpyc7dRZnTnEBd4 8uyP9jMS7QR3ijDBRgyq5L3AyYCPo737tw== X-Google-Smtp-Source: APXvYqx7Se/ijQfs6J2k9GORA/0UsUMppOuD8JOSqRuCsVgQeEecviXe/bYZtk/e5A5YYZ3jIOqGnw== X-Received: by 2002:a6b:4e1a:: with SMTP id c26mr2364220iob.122.1575383826510; Tue, 03 Dec 2019 06:37:06 -0800 (PST) Received: from [192.168.1.159] ([65.144.74.34]) by smtp.gmail.com with ESMTPSA id 3sm712249iow.71.2019.12.03.06.37.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 03 Dec 2019 06:37:05 -0800 (PST) Subject: Re: [PATCH v2] block: optimise bvec_iter_advance() To: Pavel Begunkov , nivedita@alum.mit.edu, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org References: From: Jens Axboe Message-ID: <4eb4a426-8180-ec2a-974b-2b8cdd5f285c@kernel.dk> Date: Tue, 3 Dec 2019 07:37:04 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/30/19 1:23 PM, Pavel Begunkov wrote: > bvec_iter_advance() is quite popular, but compilers fail to do proper > alias analysis and optimise it good enough. The assembly is checked > for gcc 9.2, x86-64. > > - remove @iter->bi_size from min(...), as it's always less than @bytes. > Modify at the beginning and forget about it. > > - the compiler isn't able to collapse memory dependencies and remove > writes in the loop. Help it by explicitely using local vars. Applied, thanks. -- Jens Axboe