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Tue, 21 Jan 2020 19:29:11 -0800 (PST) Received: from [192.168.43.234] ([109.126.145.157]) by smtp.gmail.com with ESMTPSA id b137sm2118126wme.26.2020.01.21.19.29.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Jan 2020 19:29:11 -0800 (PST) To: Jens Axboe , Dmitry Sychov , io-uring@vger.kernel.org References: <1f98dcc3-165e-2318-7569-e380b5959de7@kernel.dk> <77680e62-881d-5130-2d32-fc3cf5b9e065@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: Waiting for requests completions from multiple threads Message-ID: <366bcd60-f28b-4443-35d5-d8e7bfe7bba8@gmail.com> Date: Wed, 22 Jan 2020 06:28:31 +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: <77680e62-881d-5130-2d32-fc3cf5b9e065@kernel.dk> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="JuryWPpIW4zYsllZIUNoEexpV4XEJPbLL" 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) --JuryWPpIW4zYsllZIUNoEexpV4XEJPbLL Content-Type: multipart/mixed; boundary="K4hWh7hoqzl9i688PGZpTsE5AIfwDVyrZ"; protected-headers="v1" From: Pavel Begunkov To: Jens Axboe , Dmitry Sychov , io-uring@vger.kernel.org Message-ID: <366bcd60-f28b-4443-35d5-d8e7bfe7bba8@gmail.com> Subject: Re: Waiting for requests completions from multiple threads References: <1f98dcc3-165e-2318-7569-e380b5959de7@kernel.dk> <77680e62-881d-5130-2d32-fc3cf5b9e065@kernel.dk> In-Reply-To: <77680e62-881d-5130-2d32-fc3cf5b9e065@kernel.dk> --K4hWh7hoqzl9i688PGZpTsE5AIfwDVyrZ Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 22/01/2020 06:16, Jens Axboe wrote: > On 1/21/20 8:09 PM, Dmitry Sychov wrote: >> Thank you for quick reply! Yes I understand that I need a sort of >> serializable-level isolation >> when accessing the rings - I hope this could be done with a simple >> atomic cmp-add after optimistic write ring update. >=20 > That's not a bad idea, that could definitely work, and would be more > efficient than just grabbing a lock. >=20 If I got it right, it still will spam the system with atomics. There is another pattern to consider, (seen in the networking world a lot= ). Just one thread gets completions (i.e. calls io_uring_enter()), and than distr= ibutes jobs to a thread pool. And for this distribution there are a lot of way to do it efficiently. E.= g. see internal techniques in java fork join merge. That's for completion part. > Could also be made to work quite nicely with restartable sequences. I'd= > love to see liburing grow support for smarter sharing of a ring, that's= > really where that belongs. >=20 >> Correct me if I'am wrong, but from my understanding the kernel can >> start to pick up newly written Uring jobs >> without waiting for the "io_uring_enter" user level call and that's >> why we need a write barrier(so that >> the ring state is always valid for the kernel), else "io_uring_enter" >> could serve as a write barrier itself as well... >=20 > By uring jobs, you mean SQEs, or submission queue entries? The kernel > only picks up what you ask it to, it won't randomly just grab entries > from the SQ ring unless you do an io_uring_enter() and tell it to > consume N entries. The exception is if you setup the ring with > IORING_SETUP_SQPOLL, in which case the kernel will maintain a submissio= n > thread. For that case, yes, the kernel can pickup an entry as soon as > the SQ tail is updated by the application. >=20 --=20 Pavel Begunkov --K4hWh7hoqzl9i688PGZpTsE5AIfwDVyrZ-- --JuryWPpIW4zYsllZIUNoEexpV4XEJPbLL Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEE+6JuPTjTbx479o3OWt5b1Glr+6UFAl4nwWMACgkQWt5b1Glr +6WjeA/7B+0QSI2h3mG7PKPioO40DwTSVf7+pJY1IGxdY84+ZqcdCcrSgl9Q1JmA Bx70s0Y05rvjXDJ16j2xGkeIZ32Tg08jHu6ftuQLzPMotsaDEiXQMs2GM5bBvWfk nCZVoCxWPM8pHSGt8pMy+F4asvpp/E5X/9d3l9QD2sCrOm4Nk2DOVz4G1PFxnHFH lBv7hyOFyvh/UifpHMmumDfr+DN43A4WyUMuwAEMm8vI1P4VB1Z6kuUk33YnFCAh h+h5sy3emiTr6yY8OuhqzFLLQBWiySgMnL+gzkGKAfK91y/YqyuGuc6rmK0JYtSr TwSG29NGu4JH//35hcGWzmp7paxclK7FJW/lt1L1vMo6nVPMQuuxRjqLvVprD+NN rmj0mWabaj4DQo/kPgK/gbn8KR1Ys/vHh2AsXP6G/MkpRn/Qy2Jwq6EM6+zGnh4W 3/xHRnFXEOPmTxxzBS2l5TljG4IHp9V8VonaiP93S3MYHkFe8OE6S/KicEJicVlG 6RCJ2ZM2uyVM40rKEFLYEFb+E/poL7l6zF4ooa09Y4I0Q7/zwMq6iGS8ZEjETjDh R0lkDkkPRIDU6xOZmTbJqNOLqjjxG+YJAfwQ1uEJW57gm4TjhJA8mEChczasqnJw NnLX6wIi9LYzmMsMQlyZU6yE2tvcrzgScerSq3ZX5qDwLp+TqSA= =xFn0 -----END PGP SIGNATURE----- --JuryWPpIW4zYsllZIUNoEexpV4XEJPbLL--