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 BDED2C11D2F for ; Mon, 24 Feb 2020 17:17:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 86CC320836 for ; Mon, 24 Feb 2020 17:17:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="YJbLUE+q" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727359AbgBXRRR (ORCPT ); Mon, 24 Feb 2020 12:17:17 -0500 Received: from mail-wr1-f46.google.com ([209.85.221.46]:32976 "EHLO mail-wr1-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727259AbgBXRRR (ORCPT ); Mon, 24 Feb 2020 12:17:17 -0500 Received: by mail-wr1-f46.google.com with SMTP id u6so11353487wrt.0 for ; Mon, 24 Feb 2020 09:17:14 -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=KdkPsx5Fo701ZnIqORF6klJ5kZ2/Goij1JuYFr0fIhM=; b=YJbLUE+q9gHjW4VQTsSVGrg6W/4krkt09XPWL2sHnt6f0JyimES/9wiDryrh6DaUcu UeaVbenKi07KWcGcRL4q7TKohL2UtOGLVggOgDqaiMLiOFXwPoWB/QvEMNhEB6UDGoml 5flID9ZNp5d3j8hS1ifr+3Q0GEKvAixUQsHxBtobjuL0BgY3V2jq10+9DKpYp+x0RsJu WmKkV3PiMD7qKdYo9MGN5iB7pqThSW17PKMfMG0oRtbQSe4rK/mnNXdVg1u32cLhU/b/ JuOyKhwqtIpn6vKQMQWDRPv5UzntYjB91w0Z7XpDJbaLZzyIir5PtiA5Bj1v1rSRT5i6 hnZA== 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=KdkPsx5Fo701ZnIqORF6klJ5kZ2/Goij1JuYFr0fIhM=; b=X9d1sgorvz7wxxKH8HhETDfZdtq5T5H8StRJnXfxg77xQTxXLd+ZfE33u1xtOnagtf HCy74Bh4deaDj9GuJoj5OI13q9wxcVVX6jFEIDRVZdYrRW6BbAJS907KODW1sVEOze/W eTYAsAYdMWEJT152sDytr3QtO3WQDvLzzX7xWOMn5qqx73nUxcw3CkbWGATHaPB6Wg+E C/dRDRzNFl9b7jGTh5Je+Z6BZZuVTmR+MV0fDEAuzYhZfloSu5IhpnTsWUDkyyNVhFJy C//EJ5oUYARNB+5U7jPSzwIGVG1LSW2Hs4HemDmZmjLDueNCiSdHw/XgoXLBENO2FmZe Incg== X-Gm-Message-State: APjAAAVVfebilvL4Ld1OPAXGvCjPZ/AWa2oHquTSGWZZYgrt6KoFHcZO xDEd7zW7A0DzsuYK+YH98/hlCtdJ X-Google-Smtp-Source: APXvYqwefXpOn/Zk5dxebhaTm/F/uj+SIf3/IBE2RmD8CzHYiQumwrArC4Z/tfwRupRd9u1Up3pxDA== X-Received: by 2002:adf:828b:: with SMTP id 11mr6032425wrc.169.1582564633709; Mon, 24 Feb 2020 09:17:13 -0800 (PST) Received: from [192.168.43.177] ([109.126.137.65]) by smtp.gmail.com with ESMTPSA id p12sm19759415wrx.10.2020.02.24.09.17.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 24 Feb 2020 09:17:13 -0800 (PST) Subject: Re: Deduplicate io_*_prep calls? To: Andres Freund Cc: Jens Axboe , io-uring@vger.kernel.org References: <90097a02-ade0-bc9a-bc00-54867f3c24bc@kernel.dk> <20200224071211.bar3aqgo76sznqd5@alap3.anarazel.de> <933f2211-d395-fa84-59ae-0b2e725df613@kernel.dk> <23a49bca-26a6-ddbd-480b-d7f3caa16c29@gmail.com> <065ee992-7eaf-051a-e8c5-9e0e8731b3f1@kernel.dk> <746b93f0-d0b5-558a-28c7-a614b2367d91@gmail.com> <20200224170846.o54p2uv4qv4arygj@alap3.anarazel.de> 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, 24 Feb 2020 20:16:24 +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: <20200224170846.o54p2uv4qv4arygj@alap3.anarazel.de> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="3nJ50J5V2BLSvispVTQy1TuwFJdSjqWlU" 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) --3nJ50J5V2BLSvispVTQy1TuwFJdSjqWlU Content-Type: multipart/mixed; boundary="X9yrC1bviq5bl4CQaUoQ7mqugc3QxjCXa"; protected-headers="v1" From: Pavel Begunkov To: Andres Freund Cc: Jens Axboe , io-uring@vger.kernel.org Message-ID: Subject: Re: Deduplicate io_*_prep calls? References: <90097a02-ade0-bc9a-bc00-54867f3c24bc@kernel.dk> <20200224071211.bar3aqgo76sznqd5@alap3.anarazel.de> <933f2211-d395-fa84-59ae-0b2e725df613@kernel.dk> <23a49bca-26a6-ddbd-480b-d7f3caa16c29@gmail.com> <065ee992-7eaf-051a-e8c5-9e0e8731b3f1@kernel.dk> <746b93f0-d0b5-558a-28c7-a614b2367d91@gmail.com> <20200224170846.o54p2uv4qv4arygj@alap3.anarazel.de> In-Reply-To: <20200224170846.o54p2uv4qv4arygj@alap3.anarazel.de> --X9yrC1bviq5bl4CQaUoQ7mqugc3QxjCXa Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 24/02/2020 20:08, Andres Freund wrote: > Hi, >=20 > On 2020-02-24 19:18:26 +0300, Pavel Begunkov wrote: >> On 24/02/2020 19:02, Jens Axboe wrote: >>>> Usually doesn't work because of such possible "hackier assignments".= >>>> Ok, I have to go and experiment a bit. Anyway, it probably generates= a lot of >>>> useless stuff, e.g. for req->ctx >>> >>> Tried this, and it generates the same code... >> >> Maybe it wasn't able to optimise in the first place >> >> E.g. for the following code any compiler generates 2 reads (thanks god= bolt). >> >> extern void foo(int); >> int bar(const int *v) >> { >> foo(*v); >> return *v; >> } >=20 > Yea, the compiler really can't assume anything for this kind of > thing. > a) It's valid C to cast away the const here, as long as it's guaranteed= > that v isn't pointing to to actually const memory. > b) foo() could actually have access to *v without the argument, > e.g. through a global. > and even in the case of a const member of a struct, as far as I know > it's legal to change the values, as long as the allocation isn't const.= =20 Yep, regular stuff. And that's why I want to find a way to force compiler= s to think otherwise. e.g. kind of __attribute__ --=20 Pavel Begunkov --X9yrC1bviq5bl4CQaUoQ7mqugc3QxjCXa-- --3nJ50J5V2BLSvispVTQy1TuwFJdSjqWlU Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEE+6JuPTjTbx479o3OWt5b1Glr+6UFAl5UBOwACgkQWt5b1Glr +6UprQ/+MR3gK6r3rgQiaIUoXsRa18EsKIq/JBOt5MzGtmAuzHrnghcLGUQdidOj dVeJy2L/WEdAOCmh0FC5J/4ISNAJ9uBdHkCgUJiXUl+vNCBj0n7cn31hrfsmBGhl zvVkoY6SBAwUhugyiI9+0LqzJnzuecKqolH6xEVJuBBW3gr0RGsjtimBtSMDk+5y +0VqbZOvtRtZ8EzRsmg28tMNit7ZneciCRJbdqhADkY/vaMZh2hubvoTcuFNr5as LoO0quNOpE+Nd1R4yeI3XWFFAnN2WSJTF0gPbePLL7KZIsFUhhkZ/t1LdFk3enKE yayu96mC6ar8farKfADbWM5m2IsT1qAEb3Qwp1eTwgAnD2uBi/xWxyN9RHQ1R0/6 qLYonolAtikEBtoLZsdiLr2Ba1OmBcY613zF8uggbRkm2u1whFK3cs8SwyzZWieN VDciKiEftDb5B09OIPzwt6SOn2jUqYAn0hbqnWS0jHCmByNIFBrvt23OEK2ikV0k l4FjumaC7epneAw9XCVyA2XX9xZv9m5BklxJBq83EuHi6qV4Fww6uLwyi+7y43qx cRcz/TfUZzyhwpnkN9Koob2kTiXbr81wcx5jKGRNHPqb3qsBg3PWWhGWwXKck92y /P8U3NiG/IM6ngzGm8pg4K4/wMKPFe+Q4+NGpSA9v7CvppUdQk4= =aNHB -----END PGP SIGNATURE----- --3nJ50J5V2BLSvispVTQy1TuwFJdSjqWlU--