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Sat, 01 Feb 2020 03:30:50 -0800 (PST) Received: from [192.168.43.154] ([109.126.145.157]) by smtp.gmail.com with ESMTPSA id p26sm13998022wmc.24.2020.02.01.03.30.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 01 Feb 2020 03:30:49 -0800 (PST) To: Andres Freund , Jens Axboe , io-uring@vger.kernel.org References: <20200201091839.eji7fwudvozr3deb@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== Subject: Re: What does IOSQE_IO_[HARD]LINK actually mean? Message-ID: Date: Sat, 1 Feb 2020 14:30:06 +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: <20200201091839.eji7fwudvozr3deb@alap3.anarazel.de> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="7ZZUWIqY1aJnc8JsPIZFepNrSc6huQ6zZ" 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) --7ZZUWIqY1aJnc8JsPIZFepNrSc6huQ6zZ Content-Type: multipart/mixed; boundary="Hq3yl7KcrtKjLycLjfPJsO4wcRMZgjYDP"; protected-headers="v1" From: Pavel Begunkov To: Andres Freund , Jens Axboe , io-uring@vger.kernel.org Message-ID: Subject: Re: What does IOSQE_IO_[HARD]LINK actually mean? References: <20200201091839.eji7fwudvozr3deb@alap3.anarazel.de> In-Reply-To: <20200201091839.eji7fwudvozr3deb@alap3.anarazel.de> --Hq3yl7KcrtKjLycLjfPJsO4wcRMZgjYDP Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 01/02/2020 12:18, Andres Freund wrote: > Hi, >=20 > Reading the manpage from liburing I read: > IOSQE_IO_LINK > When this flag is specified, it forms a link with the n= ext SQE in the submission ring. That next SQE > will not be started before this one completes. This, in = effect, forms a chain of SQEs, which can be > arbitrarily long. The tail of the chain is denoted by th= e first SQE that does not have this flag set. > This flag has no effect on previous SQE submissions, nor = does it impact SQEs that are outside of the > chain tail. This means that multiple chains can be ex= ecuting in parallel, or chains and individual > SQEs. Only members inside the chain are serialized. Avail= able since 5.3. >=20 > IOSQE_IO_HARDLINK > Like IOSQE_IO_LINK, but it doesn't sever regardless of th= e completion result. Note that the link will > still sever if we fail submitting the parent request, har= d links are only resilient in the presence of > completion results for requests that did submit correctly= =2E IOSQE_IO_HARDLINK implies IOSQE_IO_LINK. > Available since 5.5. >=20 > I can make some sense out of that description of IOSQE_IO_LINK without > looking at kernel code. But I don't think it's possible to understand > what happens when an earlier chain member fails, and what denotes an > error. IOSQE_IO_HARDLINK's description kind of implies that > IOSQE_IO_LINK will not start the next request if there was a failure, > but doesn't define failure either. >=20 Right, after a "failure" occurred for a IOSQE_IO_LINK request, all subseq= uent requests in the link won't be executed, but completed with -ECANCELED. Ho= wever, if IOSQE_IO_HARDLINK set for the request, it won't sever/break the link a= nd will continue to the next one. > Looks like it's defined in a somewhat adhoc manner. For file read/write= > subsequent requests are failed if they are a short read/write. But > e.g. for sendmsg that looks not to be the case. >=20 As you said, it's defined rather sporadically. We should unify for it to = make sense. I'd prefer to follow the read/write pattern. > Perhaps it'd make sense to reject use of IOSQE_IO_LINK outside ops wher= e > it's meaningful? If we disregard it for either length-based operations or the rest ones (o= r whatever combination), the feature won't be flexible enough to be useful,= but in combination it allows to remove much of context switches. --=20 Pavel Begunkov --Hq3yl7KcrtKjLycLjfPJsO4wcRMZgjYDP-- --7ZZUWIqY1aJnc8JsPIZFepNrSc6huQ6zZ Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEE+6JuPTjTbx479o3OWt5b1Glr+6UFAl41YUMACgkQWt5b1Glr +6WYQxAAuUVBNx5BcJs7tqLmYwrfmJmEqqBXN4xCjVUvzWTAt1psHqOdiBCidFp7 Zo1FDoXsZxLbwXXAHmBWShTwJZ3l7v5vhs+FZJthsUq1h+A1a7hFs58HBKzPVHR8 o+MiBNnfqIALLp0itHyk5ulO0sQ9f+XsZm2Xv3ziL5gIzTfxWcL5fTs34/1jHonP ONMUsC7D8Q0yy5tO5XuJIY97wN2EZkKukYhKrgAszdWe7vhm9LUsY7LBcxQYw/zv ab6qC4pTfcpeLt56kIXL6B7a9+uxMNFKxgLQH/hOxixkcF2susUfsk88NfeTytmv yhoXhFMW4D67auuQZHV2iVddziU2QJvLFx45QDxiQkM90tztCr1nFdvACPIJbAdJ ojCRQ8OfYQmeuOvupOenZB5NJq/b7uWS0men5viGrPghoGVTsy04JRi8uSe5kZnX 6VAR1cMQzsCZU0cjrSiZxJmi8MsKgqWnDNB/MsMMWds9lUE3qplumCNu5QwXJZvM w72U15suKoIP7WU1qYTZlO/hxiEPH+dCWatd6QQK0qWcxuT/O/eBF8kICFh2lqYn GiuKvXFHwGmlSNqIgM1UaNk9Rv9tZRveI/0WUPAV/dVyGqAlSc/VBSxyb+TdgTgk bYL1VG9opPD1rb0pw7Wt0QEZjweDunKooDyYXUaE+WU4rfrFAKE= =wNkz -----END PGP SIGNATURE----- --7ZZUWIqY1aJnc8JsPIZFepNrSc6huQ6zZ--