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Mon, 24 Feb 2020 07:41:06 -0800 (PST) Received: from [192.168.43.177] ([109.126.137.65]) by smtp.gmail.com with ESMTPSA id n13sm19146602wmd.21.2020.02.24.07.41.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 24 Feb 2020 07:41:05 -0800 (PST) To: Jens Axboe , io-uring@vger.kernel.org References: <843cc96a407b2cbfe869d9665c8120bdde34683e.1582535688.git.asml.silence@gmail.com> <295a86f4-6e70-366a-e056-33894430c7aa@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== Subject: Re: [PATCH RFC] io_uring: remove retries from io_wq_submit_work() Message-ID: Date: Mon, 24 Feb 2020 18:40:18 +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: <295a86f4-6e70-366a-e056-33894430c7aa@kernel.dk> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="2Y3IsaPFIoarmMDg6dRt1ldJ9bE5svX9u" 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) --2Y3IsaPFIoarmMDg6dRt1ldJ9bE5svX9u Content-Type: multipart/mixed; boundary="FmouyxkJODbrNHOd3uHMMDmYGrvdHcHXu"; protected-headers="v1" From: Pavel Begunkov To: Jens Axboe , io-uring@vger.kernel.org Message-ID: Subject: Re: [PATCH RFC] io_uring: remove retries from io_wq_submit_work() References: <843cc96a407b2cbfe869d9665c8120bdde34683e.1582535688.git.asml.silence@gmail.com> <295a86f4-6e70-366a-e056-33894430c7aa@kernel.dk> In-Reply-To: <295a86f4-6e70-366a-e056-33894430c7aa@kernel.dk> --FmouyxkJODbrNHOd3uHMMDmYGrvdHcHXu Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 24/02/2020 18:27, Jens Axboe wrote: > On 2/24/20 2:15 AM, Pavel Begunkov wrote: >> It seems no opcode may return -EAGAIN for non-blocking case and expect= >> to be reissued. Remove retry code from io_wq_submit_work(). >=20 > There's actually a comment right there on how that's possible :-) Yeah, I saw it and understand the motive, and how it may happen, but can'= t find a line, which can actually return -EAGAIN. Could you please point to= an example? E.g. I suppose for io_read() it may happen in call_read_iter(), but its r= esult (i.e. res2) will be written to cqe, but not returned. > Normally, for block IO, we can wait for request slots if we run out. > For polled IO, that isn't possible since the task itself is the one > that will find completions and hence free request slots as well. If > the submitting task is allowed to sleep waiting for requests that it > itself are supposed to find and complete, then we'd hang. Hence we > return -EAGAIN for that case, and have no other choice for polled > IO than to retry. --=20 Pavel Begunkov --FmouyxkJODbrNHOd3uHMMDmYGrvdHcHXu-- --2Y3IsaPFIoarmMDg6dRt1ldJ9bE5svX9u Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEE+6JuPTjTbx479o3OWt5b1Glr+6UFAl5T7mYACgkQWt5b1Glr +6UylQ/+NgYSCltfm9PIAYiAmAEx4tEznpjOgTlAA+lU5oto/IjRtKVJgD+IvpxN QTv7BUGl+kNg+kOB0RTdCwOjIDxeAmb1fmebkQsMesJpHJAsef+xTTYQS/XjSVmP WhhzQ1POPs2mkmAIXebhJicv+Kqsha4YipCgzvRhapeWkqm/gXMjmOPQcZ3pVEwc jXLIw9w1qliXjmKG8wBoewN6Ru5Nr2uedQ4CrLM98Jp6s5D9uumF8fC/xVhJ6la8 AZglPULaACcf3tyEaMTHroYYJr9v6EZrjrv7j0J7Yx4rHmIHaCQ5YTQtV8I71FXk Zh8CGTJa5oEoj5jEyHQSJrCuwVqtPK1ewbCmGIRKJYPgoSGjbsg9+2s5LIUw4SLK TzdsK5a4/Ol4NoB6Y893Q49H999LrpBGc0tE0dCF6CLK5cYZR/VAPJbN8nzoFktq oVTA7ksAnF2ZCrSC2Z5daofV6y/bCRnHLSDUopK6TMcE6Gm51Zsl1/1otm0EnfuH y9X26z+qMxA1u6Rh9daEPPWDr/DxDNEKPF6IaFMWLigi0DwPn06gdBf+dmWxgDpw 5T4c8/WGep+y9APcbDEfemwRR7qR73O93hGS1JbdKhtmfW0NctJRX5Ss2r4Rju0m eAxK/ZzDLo15E8LUndHYLqYp9XCKtmeLrHEg9yu6ZP9h/h93c98= =QM5M -----END PGP SIGNATURE----- --2Y3IsaPFIoarmMDg6dRt1ldJ9bE5svX9u--