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=-2.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, 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 93374C11D2F for ; Mon, 24 Feb 2020 15:44:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4599B20838 for ; Mon, 24 Feb 2020 15:44:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Wr7Y74cS" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727837AbgBXPo6 (ORCPT ); Mon, 24 Feb 2020 10:44:58 -0500 Received: from mail-wm1-f54.google.com ([209.85.128.54]:37086 "EHLO mail-wm1-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727734AbgBXPo5 (ORCPT ); Mon, 24 Feb 2020 10:44:57 -0500 Received: by mail-wm1-f54.google.com with SMTP id a6so9931895wme.2 for ; Mon, 24 Feb 2020 07:44:55 -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; bh=Ny33y7u5/3B+EhkMccz+r1D/XcEttWNt2/FaZIEJbV0=; b=Wr7Y74cS29gMLLpvIv9H14V2zszc2gHjh27lq5BxGqll65LrWhLXtedKrQK1fBOlQr HxgKJjuW2RkRDssg2cjifcTEcDZTaBiwiOG9LMeGgoW2HYAyegJiwhXQa/Raj8a3fGuq BhOUs2Tm3OeL4WOJv0704ktrtMqnjnCK6u7Mo7ngWrY2Id0m5xGBSbGXTMIWs7ni412T Dp7f4n7jD+o7PUPnIIXCtg8buRq3k9Hi4d3j54zzXFvtAaXpbAwZnlZsIEI/w9xOCCC3 U5MSYMW52xafVyBEnoGcG0mHcBpwzTdQGwnDdm83XpaN/cBuh7lq/4xPeDIcB9DikJNu YVRA== 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; bh=Ny33y7u5/3B+EhkMccz+r1D/XcEttWNt2/FaZIEJbV0=; b=tS2T4JMq3Ag6PAXe9RO763JukI+kCWa4osfi1VZPuS/STUhvXSB1HVQEdNb8wweCOy 5CBiIrTaN/oLlyO7Htd3KryPE6JmxJ6qO94Jxg5gEa743h9jEEfgrJq0e42V3DJIUX+Z yo/9U0qUvjxBMECS9oXq7JIfiXh5O05Wze0dCd1wsGLmiDEuMpjJwwR3IAmoVt4GHvbH cBWHlDd1xeWHtxnrckMwLud26jQNljaKYfGWRzUqRap6XnuiSM4KOv3o9gt76toLhds+ x0oE7YucV7ngI+KRQcr/EhvOMgUyOZbC4ZgjZPHbQO4KyAIuBkUc4dCoMLXWvQwSWy5r 78YQ== X-Gm-Message-State: APjAAAWSBtMi9+R7VmXWsA7isqi/fc1PlkIT0AOM9sdb4c13XVJHAU3C IRYbVxGogssiaKufhdo2y9xjqQB5 X-Google-Smtp-Source: APXvYqxs7A5AH+9C09222yolq0kLv/ZMSBylBkxJSLZxfGSdXkoTY58aYIUiUwqj/BXeQICgy1ye9g== X-Received: by 2002:a1c:a1c3:: with SMTP id k186mr22711037wme.179.1582559094457; Mon, 24 Feb 2020 07:44:54 -0800 (PST) Received: from [192.168.43.177] ([109.126.137.65]) by smtp.gmail.com with ESMTPSA id c9sm18899576wmc.47.2020.02.24.07.44.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 24 Feb 2020 07:44:53 -0800 (PST) Subject: Re: Deduplicate io_*_prep calls? To: Jens Axboe , Andres Freund Cc: io-uring@vger.kernel.org References: <20200224010754.h7sr7xxspcbddcsj@alap3.anarazel.de> <20200224033352.j6bsyrncd7z7eefq@alap3.anarazel.de> <90097a02-ade0-bc9a-bc00-54867f3c24bc@kernel.dk> <20200224071211.bar3aqgo76sznqd5@alap3.anarazel.de> <933f2211-d395-fa84-59ae-0b2e725df613@kernel.dk> 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: <23a49bca-26a6-ddbd-480b-d7f3caa16c29@gmail.com> Date: Mon, 24 Feb 2020 18:44:08 +0300 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: <933f2211-d395-fa84-59ae-0b2e725df613@kernel.dk> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="vmzQiEjEfpBo6Y0RnUeaecQ9aT5wOt99q" Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --vmzQiEjEfpBo6Y0RnUeaecQ9aT5wOt99q Content-Type: multipart/mixed; boundary="8Wa6b9pTvu2EZfX3LVgbywOW7V57G0NY9"; protected-headers="v1" From: Pavel Begunkov To: Jens Axboe , Andres Freund Cc: io-uring@vger.kernel.org Message-ID: <23a49bca-26a6-ddbd-480b-d7f3caa16c29@gmail.com> Subject: Re: Deduplicate io_*_prep calls? References: <20200224010754.h7sr7xxspcbddcsj@alap3.anarazel.de> <20200224033352.j6bsyrncd7z7eefq@alap3.anarazel.de> <90097a02-ade0-bc9a-bc00-54867f3c24bc@kernel.dk> <20200224071211.bar3aqgo76sznqd5@alap3.anarazel.de> <933f2211-d395-fa84-59ae-0b2e725df613@kernel.dk> In-Reply-To: <933f2211-d395-fa84-59ae-0b2e725df613@kernel.dk> --8Wa6b9pTvu2EZfX3LVgbywOW7V57G0NY9 Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 24/02/2020 18:40, Jens Axboe wrote: > On 2/24/20 12:12 AM, Andres Freund wrote: >> Hi, >> >> On 2020-02-23 20:52:26 -0700, Jens Axboe wrote: >>> The fast case is not being deferred, that's by far the common (and ho= t) >>> case, which means io_issue() is called with sqe !=3D NULL. My worry i= s >>> that by moving it into a prep helper, the compiler isn't smart enough= to >>> not make that basically two switches. >> >> I'm not sure that benefit of a single switch isn't offset by the lower= >> code density due to the additional per-opcode branches. Not inlining >> the prepare function results in: >> >> $ size fs/io_uring.o fs/io_uring.before.o >> text data bss dec hex filename >> 75383 8237 8 83628 146ac fs/io_uring.o >> 76959 8237 8 85204 14cd4 fs/io_uring.before.o >> >> symbol size >> -io_close_prep 0000000000000066 >> -io_connect_prep 0000000000000051 >> -io_epoll_ctl_prep 0000000000000051 >> -io_issue_sqe 0000000000001101 >> +io_issue_sqe 0000000000000de9 >> -io_openat2_prep 00000000000000ed >> -io_openat_prep 0000000000000089 >> -io_poll_add_prep 0000000000000056 >> -io_prep_fsync 0000000000000053 >> -io_prep_sfr 000000000000004e >> -io_read_prep 00000000000000ca >> -io_recvmsg_prep 0000000000000079 >> -io_req_defer_prep 000000000000058e >> +io_req_defer_prep 0000000000000160 >> +io_req_prep 0000000000000d26 >> -io_sendmsg_prep 000000000000006b >> -io_statx_prep 00000000000000ed >> -io_write_prep 00000000000000cd >> >> >> >>> Feel free to prove me wrong, I'd love to reduce it ;-) >> >> With a bit of handholding the compiler can deduplicate the switches. I= t >> can't recognize on its own that req->opcode can't change between the >> switch for prep and issue. Can be solved by moving the opcode into a >> temporary variable. Also needs an inline for io_req_prep (not surpring= , >> it's a bit large). >> >> That results in a bit bigger code. That's partially because of more >> inlining: >> text data bss dec hex filename >> 78291 8237 8 86536 15208 fs/io_uring.o >> 76959 8237 8 85204 14cd4 fs/io_uring.before.o >> >> symbol size >> +get_order 0000000000000015 >> -io_close_prep 0000000000000066 >> -io_connect_prep 0000000000000051 >> -io_epoll_ctl_prep 0000000000000051 >> -io_issue_sqe 0000000000001101 >> +io_issue_sqe 00000000000018fa >> -io_openat2_prep 00000000000000ed >> -io_openat_prep 0000000000000089 >> -io_poll_add_prep 0000000000000056 >> -io_prep_fsync 0000000000000053 >> -io_prep_sfr 000000000000004e >> -io_read_prep 00000000000000ca >> -io_recvmsg_prep 0000000000000079 >> -io_req_defer_prep 000000000000058e >> +io_req_defer_prep 0000000000000f12 >> -io_sendmsg_prep 000000000000006b >> -io_statx_prep 00000000000000ed >> -io_write_prep 00000000000000cd >> >> >> There's still some unnecessary branching on force_nonblocking. The >> second patch just separates the cases needing force_nonblocking >> out. Probably not quite the right structure. >> >> >> Oddly enough gcc decides that io_queue_async_work() wouldn't be inline= d >> anymore after that. I'm quite doubtful it's a good candidate anyway? >> Seems mighty complex, and not likely to win much. That's a noticable >> win: >> text data bss dec hex filename >> 72857 8141 8 81006 13c6e fs/io_uring.o >> 76959 8237 8 85204 14cd4 fs/io_uring.before.o >> --- /tmp/before.txt 2020-02-23 21:00:16.316753022 -0800 >> +++ /tmp/after.txt 2020-02-23 23:10:44.979496728 -0800 >> -io_commit_cqring 00000000000003ef >> +io_commit_cqring 000000000000012c >> +io_free_req 000000000000005e >> -io_free_req 00000000000002ed >> -io_issue_sqe 0000000000001101 >> +io_issue_sqe 0000000000000e86 >> -io_poll_remove_one 0000000000000308 >> +io_poll_remove_one 0000000000000074 >> -io_poll_wake 0000000000000498 >> +io_poll_wake 000000000000021c >> +io_queue_async_work 00000000000002a0 >> -io_queue_sqe 00000000000008cc >> +io_queue_sqe 0000000000000391 >=20 > That's OK, it's slow path, I'd prefer it not to be inlined. >=20 >> Not quite sure what the policy is with attaching POC patches? Also sen= d >> as separate emails? >=20 > Fine like this, though easier if you inline the patches so it's easier > to comment on them. >=20 > Agree that the first patch looks fine, though I don't quite see why > you want to pass in opcode as a separate argument as it's always > req->opcode. Seeing it separate makes me a bit nervous, thinking that > someone is reading it again from the sqe, or maybe not passing in > the right opcode for the given request. So that seems fragile and it > should go away. I suppose it's to hint a compiler, that opcode haven't been changed insid= e the first switch. And any compiler I used breaks analysis there pretty easy. Optimising C is such a pain... --=20 Pavel Begunkov --8Wa6b9pTvu2EZfX3LVgbywOW7V57G0NY9-- --vmzQiEjEfpBo6Y0RnUeaecQ9aT5wOt99q Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEE+6JuPTjTbx479o3OWt5b1Glr+6UFAl5T70gACgkQWt5b1Glr +6WczA/+O/1Phkx7/GQ5XThJhxDMSGRZ4XbbR4P/sfOYBxt7PO6PuUAPCwx57GAC 6NyH7qbWO9iesMLDohfTBdeF0MVM5wcy5k7mhbAuK6Cj+awU/Mu1I0O0wR8vH7A0 PcWc7gjE9Pgz8tqjXEsN6sNP38KWh0tPwtIu/I+CIxxHouYHLJPHCPoXwcO8nNFb Q1pltWQI4H1ZsmHath037UdzJ+C8SL+6TsRv6ojeLIPE5Ni/KwHG5DT0SJ4PyJMB Y8XmjBkbihL1puy/Mo74wcIZfb0HvdfyuUQe2F2v3sKjilqA4Wn/1hlKDFncG1gd mzyZ7ZUkWADD4JSwTpEPjsZ9z32+xMdj7BAn+3/brR8eD4qcQazjmoDXimGnWdZU tfKRmlQOKqF2k76oDYxbOvkjRGjiyC3/f9Y5CR53mCBCQBt3f1WnxyKNKq6JFzrH Eh7S6OGSkhr/oFq/a+/HSszCE5t/bjwjvdqt4IALf8qA9nlVCSx23pn6eA0dXmSv in3s5vfYsoZ4s8zHQ02xmiRuy25kPqvWi+9aEvnWlZcY1l7CKDBZnwkOJNVn5OJf 0t86/slImFxYxDG17s/KqLN8q31egWt8yBPWSVVKoubXkwFjJFrT+tF3TK/kvr9W adRWHSCrGjwvDmuHzGMBndRpgyWHtkD46agKUHkKnNIUZ/HBqC4= =nTbs -----END PGP SIGNATURE----- --vmzQiEjEfpBo6Y0RnUeaecQ9aT5wOt99q--