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=-4.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, 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 2AEC9C433DB for ; Mon, 11 Jan 2021 05:35:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E4A6F224BD for ; Mon, 11 Jan 2021 05:35:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726759AbhAKFfR (ORCPT ); Mon, 11 Jan 2021 00:35:17 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35984 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725379AbhAKFfQ (ORCPT ); Mon, 11 Jan 2021 00:35:16 -0500 Received: from mail-wr1-x436.google.com (mail-wr1-x436.google.com [IPv6:2a00:1450:4864:20::436]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0FAB7C061786; Sun, 10 Jan 2021 21:34:36 -0800 (PST) Received: by mail-wr1-x436.google.com with SMTP id y17so15017645wrr.10; Sun, 10 Jan 2021 21:34:35 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:autocrypt:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=kLURNOPTiz/cA1wF9W0JF1cphEUwA7F56dOaNUie0HI=; b=q3ednVxPdJM9gsDbBW3FHEpNsipAa7X/pTQ4t/D/rmaKNlqZQxgVxlPj/LRD06Bv6o d9ttg3jPc2soAgt5ImEO07lS+wtvul03RoqRX8FggH0aqfE8dCYmmUGn5kywM3EN29Zn sej9pYRtTe0YRUAcYG6moxRiQ2iUmlosF+iBfKFJdNgVpr9qqofKD6Eo8uqQsIIKocNm BZ3KKI0yAXVxDIJg7OhBjoIQUt2jCvSbdYRQiI7u3IBkDeB2RaPk+nOj79dGK0qRF9i/ qmvIypBJiCrq9DNiB2Rf4hV2taIXXxoiLD7bkW9kijn+jOs1j54N1r4I7rRkKfCgU80L TIsQ== 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:autocrypt :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=kLURNOPTiz/cA1wF9W0JF1cphEUwA7F56dOaNUie0HI=; b=AzYdf7nYjseVpf+nstkG+Q4a33n4OXl1oTozFbH+O5Tt03F2JHBWljfEu9pFDWvr5C Oc7LTc21NjN0YILJuXhUZ/1ziGSR7TG6yIp0imuYPinUeGMz2HbQVa1d5jWCl2RZRn0T FCUhZWs0c7Jhox6bHhV8mHnS7gibjEUwfwTgiU1FxJ3ttgzDgwRf/UN+VqKOoSt/IALr j1dAcBr00QRWTzf0a3XvI7ZuqC7jFHhPi/Kt+T3RvSXQQs/3dPMqT/rUi+51t7ZEZFfq LYNCqu5tT+fodGKFKS3j8J8j0ErW7bS+EVHXRrLVQBTLKJgffHL29WAh7nxL6H2ijMkW W5pg== X-Gm-Message-State: AOAM533fpIXi4TATS8npaOPuXlSb+4MH34jiyINqrXn0KPgF3BVzftoX 9SqUyPUCE+XTGNsKkMMkkSnVluUCmB4= X-Google-Smtp-Source: ABdhPJy4NdH3sTd8gHxpwP44M24BTcydjY0PpYsjXxJpbmbMAsvZmOcN3J8+4zHlX4EWG9Xz63YRSA== X-Received: by 2002:a5d:5913:: with SMTP id v19mr14678543wrd.207.1610343274399; Sun, 10 Jan 2021 21:34:34 -0800 (PST) Received: from [192.168.8.119] ([85.255.237.6]) by smtp.gmail.com with ESMTPSA id v11sm22552703wrt.25.2021.01.10.21.34.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 10 Jan 2021 21:34:33 -0800 (PST) Subject: Re: [PATCH] target/file: don't zero iter before iov_iter_bvec To: Chaitanya Kulkarni Cc: "Martin K . Petersen" , "linux-scsi@vger.kernel.org" , "target-devel@vger.kernel.org" , "linux-kernel@vger.kernel.org" References: <34cd22d6cec046e3adf402accb1453cc255b9042.1610207523.git.asml.silence@gmail.com> <4d063dde-c710-44e3-31b9-8fb6b7e1d952@gmail.com> <68887abc-2ef4-035e-625b-84569c1b5b24@gmail.com> From: Pavel Begunkov Autocrypt: addr=asml.silence@gmail.com; prefer-encrypt=mutual; keydata= mQINBFmKBOQBEAC76ZFxLAKpDw0bKQ8CEiYJRGn8MHTUhURL02/7n1t0HkKQx2K1fCXClbps bdwSHrhOWdW61pmfMbDYbTj6ZvGRvhoLWfGkzujB2wjNcbNTXIoOzJEGISHaPf6E2IQx1ik9 6uqVkK1OMb7qRvKH0i7HYP4WJzYbEWVyLiAxUj611mC9tgd73oqZ2pLYzGTqF2j6a/obaqha +hXuWTvpDQXqcOZJXIW43atprH03G1tQs7VwR21Q1eq6Yvy2ESLdc38EqCszBfQRMmKy+cfp W3U9Mb1w0L680pXrONcnlDBCN7/sghGeMHjGKfNANjPc+0hzz3rApPxpoE7HC1uRiwC4et83 CKnncH1l7zgeBT9Oa3qEiBlaa1ZCBqrA4dY+z5fWJYjMpwI1SNp37RtF8fKXbKQg+JuUjAa9 Y6oXeyEvDHMyJYMcinl6xCqCBAXPHnHmawkMMgjr3BBRzODmMr+CPVvnYe7BFYfoajzqzq+h EyXSl3aBf0IDPTqSUrhbmjj5OEOYgRW5p+mdYtY1cXeK8copmd+fd/eTkghok5li58AojCba jRjp7zVOLOjDlpxxiKhuFmpV4yWNh5JJaTbwCRSd04sCcDNlJj+TehTr+o1QiORzc2t+N5iJ NbILft19Izdn8U39T5oWiynqa1qCLgbuFtnYx1HlUq/HvAm+kwARAQABtDFQYXZlbCBCZWd1 bmtvdiAoc2lsZW5jZSkgPGFzbWwuc2lsZW5jZUBnbWFpbC5jb20+iQJOBBMBCAA4FiEE+6Ju PTjTbx479o3OWt5b1Glr+6UFAlmKBOQCGwMFCwkIBwIGFQgJCgsCBBYCAwECHgECF4AACgkQ Wt5b1Glr+6WxZA//QueaKHzgdnOikJ7NA/Vq8FmhRlwgtP0+E+w93kL+ZGLzS/cUCIjn2f4Q Mcutj2Neg0CcYPX3b2nJiKr5Vn0rjJ/suiaOa1h1KzyNTOmxnsqE5fmxOf6C6x+NKE18I5Jy xzLQoktbdDVA7JfB1itt6iWSNoOTVcvFyvfe5ggy6FSCcP+m1RlR58XxVLH+qlAvxxOeEr/e aQfUzrs7gqdSd9zQGEZo0jtuBiB7k98t9y0oC9Jz0PJdvaj1NZUgtXG9pEtww3LdeXP/TkFl HBSxVflzeoFaj4UAuy8+uve7ya/ECNCc8kk0VYaEjoVrzJcYdKP583iRhOLlZA6HEmn/+Gh9 4orG67HNiJlbFiW3whxGizWsrtFNLsSP1YrEReYk9j1SoUHHzsu+ZtNfKuHIhK0sU07G1OPN 2rDLlzUWR9Jc22INAkhVHOogOcc5ajMGhgWcBJMLCoi219HlX69LIDu3Y34uIg9QPZIC2jwr 24W0kxmK6avJr7+n4o8m6sOJvhlumSp5TSNhRiKvAHB1I2JB8Q1yZCIPzx+w1ALxuoWiCdwV M/azguU42R17IuBzK0S3hPjXpEi2sK/k4pEPnHVUv9Cu09HCNnd6BRfFGjo8M9kZvw360gC1 reeMdqGjwQ68o9x0R7NBRrtUOh48TDLXCANAg97wjPoy37dQE7e5Ag0EWYoE5AEQAMWS+aBV IJtCjwtfCOV98NamFpDEjBMrCAfLm7wZlmXy5I6o7nzzCxEw06P2rhzp1hIqkaab1kHySU7g dkpjmQ7Jjlrf6KdMP87mC/Hx4+zgVCkTQCKkIxNE76Ff3O9uTvkWCspSh9J0qPYyCaVta2D1 Sq5HZ8WFcap71iVO1f2/FEHKJNz/YTSOS/W7dxJdXl2eoj3gYX2UZNfoaVv8OXKaWslZlgqN jSg9wsTv1K73AnQKt4fFhscN9YFxhtgD/SQuOldE5Ws4UlJoaFX/yCoJL3ky2kC0WFngzwRF Yo6u/KON/o28yyP+alYRMBrN0Dm60FuVSIFafSqXoJTIjSZ6olbEoT0u17Rag8BxnxryMrgR dkccq272MaSS0eOC9K2rtvxzddohRFPcy/8bkX+t2iukTDz75KSTKO+chce62Xxdg62dpkZX xK+HeDCZ7gRNZvAbDETr6XI63hPKi891GeZqvqQVYR8e+V2725w+H1iv3THiB1tx4L2bXZDI DtMKQ5D2RvCHNdPNcZeldEoJwKoA60yg6tuUquvsLvfCwtrmVI2rL2djYxRfGNmFMrUDN1Xq F3xozA91q3iZd9OYi9G+M/OA01husBdcIzj1hu0aL+MGg4Gqk6XwjoSxVd4YT41kTU7Kk+/I 5/Nf+i88ULt6HanBYcY/+Daeo/XFABEBAAGJAjYEGAEIACAWIQT7om49ONNvHjv2jc5a3lvU aWv7pQUCWYoE5AIbDAAKCRBa3lvUaWv7pfmcEACKTRQ28b1y5ztKuLdLr79+T+LwZKHjX++P 4wKjEOECCcB6KCv3hP+J2GCXDOPZvdg/ZYZafqP68Yy8AZqkfa4qPYHmIdpODtRzZSL48kM8 LRzV8Rl7J3ItvzdBRxf4T/Zseu5U6ELiQdCUkPGsJcPIJkgPjO2ROG/ZtYa9DvnShNWPlp+R uPwPccEQPWO/NP4fJl2zwC6byjljZhW5kxYswGMLBwb5cDUZAisIukyAa8Xshdan6C2RZcNs rB3L7vsg/R8UCehxOH0C+NypG2GqjVejNZsc7bgV49EOVltS+GmGyY+moIzxsuLmT93rqyII 5rSbbcTLe6KBYcs24XEoo49Zm9oDA3jYvNpeYD8rDcnNbuZh9kTgBwFN41JHOPv0W2FEEWqe JsCwQdcOQ56rtezdCJUYmRAt3BsfjN3Jn3N6rpodi4Dkdli8HylM5iq4ooeb5VkQ7UZxbCWt UVMKkOCdFhutRmYp0mbv2e87IK4erwNHQRkHUkzbsuym8RVpAZbLzLPIYK/J3RTErL6Z99N2 m3J6pjwSJY/zNwuFPs9zGEnRO4g0BUbwGdbuvDzaq6/3OJLKohr5eLXNU3JkT+3HezydWm3W OPhauth7W0db74Qd49HXK0xe/aPrK+Cp+kU1HRactyNtF8jZQbhMCC8vMGukZtWaAwpjWiiH bA== Message-ID: Date: Mon, 11 Jan 2021 05:31:00 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/01/2021 05:23, Chaitanya Kulkarni wrote: > On 1/10/21 18:32, Pavel Begunkov wrote: >> On 11/01/2021 02:06, Chaitanya Kulkarni wrote: >>> On 1/9/21 13:29, Pavel Begunkov wrote: >>>> On 09/01/2021 20:52, Chaitanya Kulkarni wrote: >>>>> On 1/9/21 12:40, Pavel Begunkov wrote: >>>>>> I expect you won't find any, but such little things can pile up >>>>>> into a not-easy-to-spot overhead over time. >>>>> That is what I suspected with the resulting assembly. The commit log >>>>> needs to document that there is no direct impact on the performance >>>> It's obvious that 3-4 extra mov $0 off(%reg) won't change performance >>>> but still hasn't been formally confirmed ... >>> This is obvious for you and me since we spent time into looking into >>> resulting assembly not every reviewer is expected to do that see [1]. >>>>> which can be seen with this patch, but this is nice to have >>>> ... so if you don't mind, I won't be resending just for that. >>> As per commit log guidelines [1] you have to quantify the optimization. >>> >>> Since you cannot quantify the optimization modify the commit log explaining >> And then you see "Optimizations usually aren’t free but trade-offs >> between", and the patch doesn't fall under it. > First part applies to all the optimizations with and without tradeoffs > "Quantify optimizations and trade-offs." > The later part doesn't mean optimizations without trade-offs should be > allowed without having any supportive data. >> >> Let me be frank, I see it more like as a whim. If the maintainer agrees >> with that strange requirement of yours and want to bury it under >> bureaucracy, fine by me, don't take it, I don't care, but I haven't >> ever been asked here to do that for patches as this. > I didn't write the commit log guidelines, as a reviewer I'm following them. > The patch commit log claims optimization with neither having any data nor > having the supporting fact ("possibly no observable difference but in the > long term it matters") for the completeness. >> It's not "I cannot" but rather "I haven't even tried to and expect...". >> Don't mix, there is a huge difference between. > Then provide the numbers to support your claim. What claim? I didn't make any regarding performance, you may want to re-read the commit message. Anyway, I'll halt replying to this topic. Nothing personal, but it's getting annoying. -- Pavel Begunkov