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Sat, 09 Nov 2019 03:16:47 -0800 (PST) Received: from [192.168.43.163] ([109.126.130.90]) by smtp.gmail.com with ESMTPSA id l26sm1474241wme.6.2019.11.09.03.16.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 09 Nov 2019 03:16:47 -0800 (PST) To: Jens Axboe , io-uring@vger.kernel.org References: <33958a03-6714-ce51-9856-1dcbf53f67d5@kernel.dk> <273391a6-1def-3c29-986c-8efca569fc16@gmail.com> 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: limit inflight IO Message-ID: <69985522-3e8e-102b-c8e9-ea9046cd22c6@gmail.com> Date: Sat, 9 Nov 2019 14:16:28 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.0 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="eW7EDb5mt7jaRM6T1INnGG1Kbj1KPEhhe" 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) --eW7EDb5mt7jaRM6T1INnGG1Kbj1KPEhhe Content-Type: multipart/mixed; boundary="cxrDoc9UWTMq07gbLIrLfM3mlT73TPq0k"; protected-headers="v1" From: Pavel Begunkov To: Jens Axboe , io-uring@vger.kernel.org Message-ID: <69985522-3e8e-102b-c8e9-ea9046cd22c6@gmail.com> Subject: Re: [PATCH RFC] io_uring: limit inflight IO References: <33958a03-6714-ce51-9856-1dcbf53f67d5@kernel.dk> <273391a6-1def-3c29-986c-8efca569fc16@gmail.com> In-Reply-To: --cxrDoc9UWTMq07gbLIrLfM3mlT73TPq0k Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable > I've been struggling a bit with how to make this reliable, and I'm not > so sure there's a way to do that. Let's say an application sets up a > ring with 8 sq entries, which would then default to 16 cq entries. With= > this patch, we'd allow 16 ios inflight. But what if the application doe= s >=20 > for (i =3D 0; i < 32; i++) { > sqe =3D get_sqe(); > prep_sqe(); > submit_sqe(); > } >=20 > And then directly proceeds to: >=20 > do { > get_completions(); > } while (has_completions); >=20 > As long as fewer than 16 requests complete before we start reaping, > we don't lose any events. Hence there's a risk of breaking existing > setups with this, even though I don't think that's a high risk. >=20 I think, this should be considered as an erroneous usage of the API. It's better to fail ASAP than to be surprised in a production system, because of non-deterministic nature of such code. Even worse with trying to debug such stuff.=20 As for me, cases like below are too far-fetched for (i =3D 0; i < n; i++) submit_read_sqe() for (i =3D 0; i < n; i++) { device_allow_next_read() get_single_cqe() } > We probably want to add some sysctl limit for this instead. But then > the question is, what should that entry (or entries) be? >=20 --=20 Pavel Begunkov --cxrDoc9UWTMq07gbLIrLfM3mlT73TPq0k-- --eW7EDb5mt7jaRM6T1INnGG1Kbj1KPEhhe Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEE+6JuPTjTbx479o3OWt5b1Glr+6UFAl3GoAwACgkQWt5b1Glr +6VUng/+L/Jv05p8kJwMI5R4EpmCf6mizhRAc3n/AwQ2z8fNigMwp3/GYrSKlr4M rd3PhytHs4VCDq552jW+/RcJAAspT0+vzgAafcvjQsQOYzpbdAyM4YXQq0uUNRLe 9I+vt9tekOvzUTot1eYyMLmBQg+OksoSSVJWc4krlzFajBI1w46+x7nfLwgLRvRy gKF4y5MsfEz9q7Yi+Sw3rhzFLDhSwnlbSB4YAx8/rxhwBAQ/PouBnVclrHkVpXLq fUqvPCKDZJpuaNXVDsMcLaLlcjPrCJVVHfPWnOtA7gFldWxXzoXxFwyFVeXMVqB1 AbtIk7+lPtc3hqCBz+Nx9hWkjF2llDOMpjDGArQqliBH9lWru9msXWKT/rjhhjsW 16SkrVl836DEwNGSaKIvY36ASeOLfVWN+JbfXzTw2yCF0E+Ng3KBYASsH1VFFhZz VezWYkIoXB5zg/mpSzj5ZZ5yqoa/XUGDJct19asA6cnrvaH3qSuDWzOnXKEiHxeP 8my3oRKqyVnyiLGr3cWM8DJHnvnYdXJ30C4Vb8RhHDdPNqCb0T3nTK3v8dmTPUOJ ujPCIjfR4a+S9BSVV6hozROvGngtll88bvTk2kT81IoXar3bw+iU+DQ1INNyONx/ grjefyMjGJ3Mdyj83B8GEQtIvx+KcSsMwYxOQq4nyeM2O6HhbMU= =q1XF -----END PGP SIGNATURE----- --eW7EDb5mt7jaRM6T1INnGG1Kbj1KPEhhe--