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Sat, 09 Nov 2019 11:25:18 -0800 (PST) Received: from [192.168.43.77] ([109.126.135.169]) by smtp.gmail.com with ESMTPSA id n23sm9457543wmc.18.2019.11.09.11.25.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 09 Nov 2019 11:25:17 -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> <69985522-3e8e-102b-c8e9-ea9046cd22c6@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: <45560c7f-08a3-afc9-c078-a5cc944d6455@gmail.com> Date: Sat, 9 Nov 2019 22:24:59 +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="ug3r0ZohTrTfYrDKiDlAXInT0eH7wZr9i" 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) --ug3r0ZohTrTfYrDKiDlAXInT0eH7wZr9i Content-Type: multipart/mixed; boundary="PSE8Jai5f3mL55DAquEeL0f2PQO4cnDZ8"; protected-headers="v1" From: Pavel Begunkov To: Jens Axboe , io-uring@vger.kernel.org Message-ID: <45560c7f-08a3-afc9-c078-a5cc944d6455@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> <69985522-3e8e-102b-c8e9-ea9046cd22c6@gmail.com> In-Reply-To: --PSE8Jai5f3mL55DAquEeL0f2PQO4cnDZ8 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 09/11/2019 17:23, Jens Axboe wrote: > On 11/9/19 4:16 AM, Pavel Begunkov wrote: >>> I've been struggling a bit with how to make this reliable, and I'm no= t >>> 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. Wi= th >>> this patch, we'd allow 16 ios inflight. But what if the application d= oes >>> >>> for (i =3D 0; i < 32; i++) { >>> sqe =3D get_sqe(); >>> prep_sqe(); >>> submit_sqe(); >>> } >>> >>> And then directly proceeds to: >>> >>> do { >>> get_completions(); >>> } while (has_completions); >>> >>> 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. >>> >> >> 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. >> >> 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() >> } >=20 > I can't really disagree with that, it's a use case that's bound to fail= > every now and then... >=20 > But if we agree that's the case, then we should be able to just limit > based on the cq ring size in question. >=20 > Do we make it different fro CQ_NODROP and !CQ_NODROP or not? Because th= e > above case would work with CQ_NODROP, reliably. At least CQ_NODROP is > new so we get to set the rules for that one, they just have to make > sense. >=20 =2E..would work reliably... and also would let user know about stalling (-EBUSY). I thinks it's a good idea to always do CQ_NODROP, as in the backlogged patch update. --=20 Pavel Begunkov --PSE8Jai5f3mL55DAquEeL0f2PQO4cnDZ8-- --ug3r0ZohTrTfYrDKiDlAXInT0eH7wZr9i Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEE+6JuPTjTbx479o3OWt5b1Glr+6UFAl3HEowACgkQWt5b1Glr +6VkwA//e7Gfr85JpaFUE7yPHHjAua1HnjxO7FMoip7HOF+kZBwJjUtR3VVhN0iC GCU0nkU6CUUW7wyACufVqC0/wJJAkpxOCrddnJORW4oqXZ3MZJCO9UWezLe87oQS deKHRPnrweu+clvsNEbwu/03Xl1TvEK6x+1yjA0AwJZTMX5ildcZZZac8cmXzMrv MKMxdQijNqsBxQInMcUSQgawtWCKmVDOtxx80spq74Fl3QGcAWjnNCy8SA68CIVe YHQM2Ykx++O0iv+yPMN/m2VW3jr0lIj4AL6wBIG9BzYSmuzyMaf+2B/KKC4wfSoQ oOAak5V/PatsT0drtku91qahFrnlvmALBbSU+fA+gXDSo+YFH+EmbevGIEM+BXPs EwRvYmETHRxcF/j97ds15XBB+R3JFyABPVDT0p0g0ze+8EmntjX00xf4Qrqr8koU bKLrXAN0obKxGGdsrl8o5lz7LOtP3WOtpxyPAKHrGvcs5vk3og661sf00KbHLOu+ qUmrwBzB83Ml8w5jdfb/XqOTyeZu/BMJwRKhCYEjhyOPaTXZ+YDZkDIjEzA36YT/ hA4GcL6atqZkvr5QyhjNRbLu5BBkCYhCN46lAZVxOjAp/hx6a0sJdqreUsfAjcP3 heZDFli8o2YhIz9C2FBydbN+alXdTuE2Dp30OAENsbIO0a7Fr1k= =f7kk -----END PGP SIGNATURE----- --ug3r0ZohTrTfYrDKiDlAXInT0eH7wZr9i--