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Wed, 03 Jun 2020 07:48:44 -0700 (PDT) To: Xiaoguang Wang , io-uring@vger.kernel.org Cc: axboe@kernel.dk, joseph.qi@linux.alibaba.com, yujian.wu1@gmail.com References: <20200520115648.6140-1-xiaoguang.wang@linux.alibaba.com> <3bea8be7-2a82-cf24-a8b6-327672a64535@gmail.com> <242c17f3-b9b3-30cb-ff3d-a33aeef36ad1@linux.alibaba.com> <13dd7a1f-63df-6a0c-74ed-d5ff12a0bf96@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] io_uring: create percpu io sq thread when IORING_SETUP_SQ_AFF is flagged Message-ID: Date: Wed, 3 Jun 2020 17:47:24 +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: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 26/05/2020 17:42, Xiaoguang Wang wrote: > Yes, I don't try to make all io_uring instances in the system share threads, I just > make io_uring instances which are bound to same cpu core, share one io_sq_thread that > only is created once for every cpu core. > Otherwise in current io_uring mainline codes, we'd better not bind different io_uring > instances to same cpu core,  some instances' busy loop in its sq_thread_idle period will > impact other instanes who currently there are reqs to handle. I got a bit carried away from your initial case, but there is the case: Let's we have 2 unrelated apps that create SQPOLL io_uring instances. Let's say they are in 2 different docker container for the argument (and let's just assume a docker container user can create such). The first app1 submits 32K fat requests as described before. The second one (app2) is a low-latency app, submits reqs by 1, but expects it to be picked really fast. And let's assume their SQPOLL threads pinned to the same CPU. 1. old version: The CPU spends some time allocated by a scheduler on 32K requests of app1, probably not issuing them all but that's fine. And then it goes to the app2. So, the submit-to-pickup latency for app2 is capped by a task scheduler. That's somewhat fair. 2. your version: io_sq_thread first processes all 32K of requests of app1, and only then goes to app2. app2 is screwed, unfair as life can be. And a malicious user can create many io_uring instances as in app1. So the latency will be further multiplied. Any solution I can think of is ugly and won't ever land upstream. Like creating your own scheduling framework for io_uring, wiring kindof cgroups, etc. And actually SQPOLL shouldn't be so ubiquitous (+needs privileges). E.g. I expect there will be a single app per system using it, e.g. a database consuming most of the resources anyway. And that's why I think it's better to not trying to solve your original issue. However, what the patch can be easily remade into is sharing an SQPOLL thread between io_uring instances of a single app/user, like passing fd described before. The most obvious example is to share 1 SQPOLL thread (or N << num_cpus) between all user threads, so - still creating io_uring per thread to not synchronise SQ - retaining CPU time for real user work (instead of having N SQPOLL threads) - increasing polling efficiency (more work -- less idle polling) - and scheduling/task migration, etc. note: would be great to check, that it has all necessary cond_resched() > >> specified set of them. In other words, making yours @percpu_threads not global, >> but rather binding to a set of io_urings. >> >> e.g. create 2 independent per-cpu sets of threads. 1st one for {a1,a2,a3}, 2nd >> for {b1,b2,b3}. >> >> a1 = create_uring() >> a2 = create_uring(shared_sq_threads=a1) >> a3 = create_uring(shared_sq_threads=a1) >> >> b1 = create_uring() >> b2 = create_uring(shared_sq_threads=b1) >> b3 = create_uring(shared_sq_threads=b1) > Thanks your suggestions, I'll try to consider it in V2 patch. > > But I still have one question: now "shared_sq_threads=a1" and "shared_sq_threads=b1" > can be bound to same cpu core? I think it's still not efficient. E.g. "shared_sq_threads=a1" > busy loop in its sq_thread_idle period will impact shared_sq_threads=b1 who currently > there are reqs to handle. > > Now I also wonder whether a io_uring instance,which has SQPOLL enabed and does not > specify a sq_thread_cpu, can be used in real business environment, the io_sq_thread > may run in any cpu cores, which may affect any other application, e.g. cpu resource > contend. So if trying to use SQPOLL, we'd better allocate specified cpu. I think it's ok. - needs privileges to create SQPOLL - don't expect it used without thinking twice - for not-pinned case everything will be rescheduled to other cpus as appropriate It shouldn't affect much in normal circumstances. -- Pavel Begunkov