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Sat, 01 Feb 2020 07:28:56 -0800 (PST) Received: from [192.168.43.154] ([109.126.145.157]) by smtp.gmail.com with ESMTPSA id y7sm15010089wrr.56.2020.02.01.07.28.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 01 Feb 2020 07:28:56 -0800 (PST) To: Andres Freund Cc: Jens Axboe , io-uring@vger.kernel.org References: <20200201091839.eji7fwudvozr3deb@alap3.anarazel.de> <20200201120229.l7krkt6zstiruckf@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 18:28:12 +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: <20200201120229.l7krkt6zstiruckf@alap3.anarazel.de> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="cVJj2cBW87o0jxY5taEqrdK1ofi5aTvzS" 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) --cVJj2cBW87o0jxY5taEqrdK1ofi5aTvzS Content-Type: multipart/mixed; boundary="9mfaamrxrZ0oMHBEvwup6BJ0VKawoVAmK"; protected-headers="v1" From: Pavel Begunkov To: Andres Freund Cc: 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> <20200201120229.l7krkt6zstiruckf@alap3.anarazel.de> In-Reply-To: <20200201120229.l7krkt6zstiruckf@alap3.anarazel.de> --9mfaamrxrZ0oMHBEvwup6BJ0VKawoVAmK Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 01/02/2020 15:02, Andres Freund wrote: >> Right, after a "failure" occurred for a IOSQE_IO_LINK request, all sub= sequent >> requests in the link won't be executed, but completed with -ECANCELED.= However, >> if IOSQE_IO_HARDLINK set for the request, it won't sever/break the lin= k and will >> continue to the next one. >=20 > I think something along those lines should be added to the manpage... I= > think severing the link isn't really a good description, because it's > not like it's separating off the tail to be independent, or such. If > anything it's the opposite. >=20 >=20 >>> Looks like it's defined in a somewhat adhoc manner. For file read/wri= te >>> subsequent requests are failed if they are a short read/write. But >>> e.g. for sendmsg that looks not to be the case. >>> >> >> 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. >=20 > I think one problem with that is that it's not necessarily useful to > insist on the length being the maximum allowed length. E.g. for a > recvmsg you'd likely want to not fail the request if you read less than= > what you provided for, because that's just a normal occurance. It could= > e.g. be useful to just start the next recv (with a different buffer) > immediately> I'm not even sure it's generally sensible for read either,= as that > doesn't work well for EOF, non-file FDs, ... Perhaps there's just no > good solution though. People already asked about such stuff, you can find the discussion somewh= ere in github issues for liburing. In short, there are a lot of different patter= ns, and that's not viable to implement them in the kernel. There are thoughts, id= eas and plans around using BPF to deal with that. I've sent LSF/MM/BPF topic proposal exactly about that. >=20 >=20 >>> Perhaps it'd make sense to reject use of IOSQE_IO_LINK outside ops wh= ere >>> it's meaningful? >> >> If we disregard it for either length-based operations or the rest ones= (or >> whatever combination), the feature won't be flexible enough to be usef= ul, >> but in combination it allows to remove much of context switches. >=20 > I really don't want to make it less useful ;) - In fact I'm pretty > excited about having it. I haven't yet implemented / benchmarked that, > but I think for databases it is likely to be very good to achieve low > but consistent IO queue depths for background tasks like checkpointing,= > readahead, writeback etc, while still having a low context switch > rates. Without something like IOSQE_IO_LINK it's considerably harder to= > have continuous IO that doesn't impact higher priority IO like journal > flushes. >=20 > Andres Freund >=20 --=20 Pavel Begunkov --9mfaamrxrZ0oMHBEvwup6BJ0VKawoVAmK-- --cVJj2cBW87o0jxY5taEqrdK1ofi5aTvzS Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEE+6JuPTjTbx479o3OWt5b1Glr+6UFAl41mQwACgkQWt5b1Glr +6Wrjw/+I3H5NGbpZY6Cn1m0SCEmPMy0R+O7ClqP2xibfLX/DnyWGyr+pno2H+Zh 8sr7yprwRwKo+n4BHCVsxSv7VPPkkuBsq883fSysWY9OS8b49wLnFsyPI53uHGZc bfQT4/vt1+ByGzelaUFtJmlMLMO+JOVB67GyTwcgGUj9yv3G57Q/XV6NBRVd3tNu vOvBEj3JY4JNvYTORm4wqcV3zr4KDrYLHz76+rH4TVY3rldz8Y4vQQEjBuSDBhcT yvY87frOKpwR7aADomoImpIzvN8ueIrlhIUMRjvYJezyTR3cE9TtRO8lYF+qNA4g jFeKpsjxD+P5rUxs936aXSGGh0yx3jF3GCe5PcO7KqZziMhTXTqLSrCdioqUAMC0 7i0nQW7SNZoS+ID/5IAa4/2iRGpyHU2ahBMSABvYlmUIellnPNysySdjMCT4dn28 7SeggzCq6zUiZavISmHjRwvLwveMjLWsMyKBw9L/CN12UDqmnHBBXyukT3NiOx1S 3z2v8bUXNWQjveO2CdGBW1W7mkDmJp4IzI5Jn1ECWR4RijHKz8v9dsru6we5ogT6 sF40shr51OEd+vARxMZONrasfcsnxECEVCU4RPlqPRoxDQVAFXWsg/4rvlkCCJFj yoVmF87xPggJ/v0FGJFHgJVjp9UG8KG39aKgsTmHhKnida7S6WY= =rEMm -----END PGP SIGNATURE----- --cVJj2cBW87o0jxY5taEqrdK1ofi5aTvzS--