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=-9.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,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 65CCCC2BBCA for ; Tue, 15 Dec 2020 11:27:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0826522258 for ; Tue, 15 Dec 2020 11:27:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729070AbgLOL1i (ORCPT ); Tue, 15 Dec 2020 06:27:38 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42348 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729063AbgLOL1f (ORCPT ); Tue, 15 Dec 2020 06:27:35 -0500 Received: from mail-wr1-x442.google.com (mail-wr1-x442.google.com [IPv6:2a00:1450:4864:20::442]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 93034C06179C; Tue, 15 Dec 2020 03:26:55 -0800 (PST) Received: by mail-wr1-x442.google.com with SMTP id d26so6261533wrb.12; Tue, 15 Dec 2020 03:26:55 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=to:cc:references:from:autocrypt:subject:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=cZpu9JVXhyiWelTl46Pe/xlISF8M49kKFY6TqjVIyqw=; b=aXVK4L4avY9bV+Cz/0bzjSeCqzCJaFN0YJu7Etbnuszao4fnxJjx1/XTBjU4wVOd18 jT1L407QtX3yRZ9cQKwyOaH67FpaP+ZOFhSl1qIWeXvK/Fwk/9nTz27z+4EkvwZncAyL TWMmELiBQ5L6VybGZmcESTEZnNdI1dXkbblqyFgyTUspMCKD04dGNy+E82u7lQ0ERuSy ezaUwc4KbTbWA2lDEpJzmlM1MATNCPs2fbqbucnS6/+xHCcsMKzH5fdKwyRSuBCbXr87 ZTrz/n3pet5nUoi+snIqMiulRftnOZ2VW4zNxRFMTvfYgySlgnjNwsMfE+bi3e6OAd+R xYdw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:to:cc:references:from:autocrypt:subject :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=cZpu9JVXhyiWelTl46Pe/xlISF8M49kKFY6TqjVIyqw=; b=Mn7zzjR2wi+O8WSzt8KYIzOaKpP2i09AzhI1FunGDEpCubSEDm1VvRh7ns6px6AJDR G12jdqBdz4soLRzH/oDsAlGH/AtAyHeWTtECbMOYdxGEon3VrOAyxIntZ1QrY3FpSDvM EHslFJYGkJDlS3wn/onV0ewPwNPkAbl9BP9RBtW8oIMZVxxfmcha4yXzrUbOhg26FxJz irJsuea086DeqHo4HRGCZWd3mWZB71x7SW0lDRfVIXQ7rbfamf7/MhdWEjouBtEAOdhd 7U6bw0eb5dkfxBu8VBHxIqF8qdCfR1X0RNhCpXlqwQOInLCDotQyNreBYpJkNlwMCvLp +UqA== X-Gm-Message-State: AOAM532c1GrvzI/rOYIlmN5l9IEGB2Oa6QtfAmbDsF0dwCnO6w8g9KuD 9WcnTewS+w7m2EkHBIH7YiGgTtNszGSg3Drk X-Google-Smtp-Source: ABdhPJxEug64Og3Z6dTRv7LWKBBzRMmfwovjQ+k+KkNwe51YTNZYqdU/TPzDt3NqBpn2gs92QGbMLw== X-Received: by 2002:a5d:4d02:: with SMTP id z2mr34466243wrt.109.1608031614170; Tue, 15 Dec 2020 03:26:54 -0800 (PST) Received: from [192.168.8.128] ([185.69.145.6]) by smtp.gmail.com with ESMTPSA id l7sm35838949wme.4.2020.12.15.03.26.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 15 Dec 2020 03:26:53 -0800 (PST) To: David Laight , "linux-block@vger.kernel.org" Cc: Jens Axboe , Christoph Hellwig , Matthew Wilcox , Ming Lei , Johannes Weiner , Alexander Viro , "Darrick J . Wong" , "Martin K . Petersen" , Jonathan Corbet , "linux-xfs@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "io-uring@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "target-devel@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "linux-doc@vger.kernel.org" References: <5c9c22dbeecad883ca29b31896c262a8d2a77132.1607976425.git.asml.silence@gmail.com> <262132648a8f4e7a9d1c79003ea74b3f@AcuMS.aculab.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== Subject: Re: [PATCH v1 2/6] iov_iter: optimise bvec iov_iter_advance() Message-ID: Date: Tue, 15 Dec 2020 11:23:34 +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: <262132648a8f4e7a9d1c79003ea74b3f@AcuMS.aculab.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 15/12/2020 09:37, David Laight wrote: > From: Pavel Begunkov >> Sent: 15 December 2020 00:20 >> >> iov_iter_advance() is heavily used, but implemented through generic >> iteration. As bvecs have a specifically crafted advance() function, i.e. >> bvec_iter_advance(), which is faster and slimmer, use it instead. >> >> lib/iov_iter.c | 19 +++++++++++++++++++ [...] >> void iov_iter_advance(struct iov_iter *i, size_t size) >> { >> if (unlikely(iov_iter_is_pipe(i))) { >> @@ -1077,6 +1092,10 @@ void iov_iter_advance(struct iov_iter *i, size_t size) >> i->count -= size; >> return; >> } >> + if (iov_iter_is_bvec(i)) { >> + iov_iter_bvec_advance(i, size); >> + return; >> + } >> iterate_and_advance(i, size, v, 0, 0, 0) >> } > > This seems to add yet another comparison before what is probably > the common case on an IOVEC (ie normal userspace buffer). If Al finally takes the patch for iov_iter_is_*() helpers it would be completely optimised out. > > Can't the call to bver_iter_advance be dropped into the 'advance' > path for BVEC's inside iterate_and_advance? It iterates by page/segment/etc., why would you want to do bver_iter_advance(i->count) there? > > iterate_and_advance itself has three 'unlikely' conditional tests > that may be mis-predicted taken before the 'likely' path. > One is for DISCARD which is checked twice on the object I just > looked at - the test in iov_iter_advance() is pointless. And again, both second checks, including for discards, would be optimised out by the iov_iter_is_* patch. -- Pavel Begunkov