From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5894BC433DF for ; Wed, 13 May 2020 16:03:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 82AA3205ED for ; Wed, 13 May 2020 16:03:30 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="pV8GrHZ2" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730291AbgEMQD3 (ORCPT ); Wed, 13 May 2020 12:03:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51180 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730063AbgEMQD3 (ORCPT ); Wed, 13 May 2020 12:03:29 -0400 Received: from mail-wr1-x42a.google.com (mail-wr1-x42a.google.com [IPv6:2a00:1450:4864:20::42a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8B4E3C061A0C for ; Wed, 13 May 2020 09:03:27 -0700 (PDT) Received: by mail-wr1-x42a.google.com with SMTP id l18so65566wrn.6 for ; Wed, 13 May 2020 09:03:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=to:cc:references:from:autocrypt:subject:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=PXp6AteMxo6nougODUALPWvTRnz4YKG8qKKWMAQqx7Y=; b=pV8GrHZ2r3C2tnUuQ9vFmtwlaPEiOhkOVu5ymmUNVkeTmc9muJdP+t2u8dS5wGFZ29 fg+BQf+WUC6+qyXibMTdNSrfKIfoPg92XqZvn/2CkBlhVfIeMy6DRSw5H5NMoPuG/Spn 2cx5yqD8nHcDAJrsN7Q09wIXkRe95HtAfHKkDnwjqq7Q2/vY/QjcPS7hRWBWPjUK3tSM u+EVVq0OBr6nTGXldP3rhih9/nlUMReXTQYwE38qS8rwQSBvmRfQalFVmKiJMcRgOzek kXvVzGftjSfb11y9zehnrDdK5L21qmZYyHztj3ajlZ/IiwUnTEEASudDDjIj6WTztSQu i3Tg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:to:cc:references:from:autocrypt:subject :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=PXp6AteMxo6nougODUALPWvTRnz4YKG8qKKWMAQqx7Y=; b=Tqv78qClkIS5ud05kmyo873VVxRj9j02V7H9d/rT7gid67cyHGbhNK1u5UKhWcCZPL aSQB46jt0nk99XvXT1f78/GpPM0iMRE+jmtt+1PCQmwQ+hj7hB4g+fuYt9mW3Xz0HDCS C78PdlU1V1GH/x1yS0bUDfDSfzQ9v4QRMI8ViUL2inVUpp0oh/eTRe5ROpDyAxMhpy71 ndJ/SDrHLzZi3/qXaUG2BGbAssyooJbV7AOfpBxl070wOTitH4+63W0rZj9caVMBw4gN 0n8cqWRQrlVNCN9Rsfrcbaoxqt4FLP4mj+yLmrOVGshXceI9fGxrW1fiJ+R0e03GOixM 5yOw== X-Gm-Message-State: AOAM531P4GOcv8iDnjisdRaS+fMj9PvaZeULnE0wUcvcLCQvYEGh+p6q hN5YXAmiFkMExE6u8A8tXrR79xj0 X-Google-Smtp-Source: ABdhPJw5WfiMPzlztd64TqLJIcQ+1aZ55xIDT8V4ak+Z2x4fUnwJMG3CZjZgArGsvG8k1+1Jq2LfMQ== X-Received: by 2002:adf:fe90:: with SMTP id l16mr63585wrr.222.1589385805885; Wed, 13 May 2020 09:03:25 -0700 (PDT) Received: from [192.168.43.127] ([46.191.65.149]) by smtp.gmail.com with ESMTPSA id r9sm19277309wmg.47.2020.05.13.09.03.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 13 May 2020 09:03:25 -0700 (PDT) To: Dmitry Sychov , Sergiy Yevtushenko Cc: Mark Papadakis , "H. de Vries" , io-uring References: <7692E70C-A0EA-423B-883F-6BF91B0DB359@icloud.com> <2F012CBD-7DB6-4E88-BFFE-63427B0DD18D@icloud.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: Any performance gains from using per thread(thread local) urings? Message-ID: Date: Wed, 13 May 2020 19:02:15 +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 13/05/2020 17:22, Dmitry Sychov wrote: > Anyone could shed some light on the inner implementation of uring please? :) It really depends on the workload, hardware, etc. io_uring instances are intended to be independent, and each have one CQ and SQ. The main user's concern should be synchronisation (in userspace) on CQ+SQ. E.g. 100+ cores hammering on a spinlock/mutex protecting an SQ wouldn't do any good. Everything that can't be inline completed\submitted during io_urng_enter(), will be offloaded to an internal thread pool (aka io-wq), which is per io_uring by default, but can be shared if specified. There are pros and cons, but I'd recommend first to share a single io-wq, and then experiment and tune. Also, in-kernel submission is not instantaneous and done by only thread at any moment. Single io_uring may bottleneck you there or add high latency in some cases. And there a lot of details, probably worth of a separate write-up. > > Specifically how well kernel scales with the increased number of user > created urings? Should scale well, especially for rw. Just don't overthrow the kernel with threads from dozens of io-wqs. > >> If kernel implementation will change from single to multiple queues, >> user space is already prepared for this change. > > Thats +1 for per-thread urings. An expectation for the kernel to > become better and better in multiple urings scaling in the future. > > On Wed, May 13, 2020 at 4:52 PM Sergiy Yevtushenko > wrote: >> >> Completely agree. Sharing state should be avoided as much as possible. >> Returning to original question: I believe that uring-per-thread scheme is better regardless from how queue is managed inside the kernel. >> - If there is only one queue inside the kernel, then it's more efficient to perform multiplexing/demultiplexing requests in kernel space >> - If there are several queues inside the kernel, then user space code better matches kernel-space code. >> - If kernel implementation will change from single to multiple queues, user space is already prepared for this change. >> >> >> On Wed, May 13, 2020 at 3:30 PM Mark Papadakis wrote: >>> >>> >>> >>>> On 13 May 2020, at 4:15 PM, Dmitry Sychov wrote: >>>> >>>> Hey Mark, >>>> >>>> Or we could share one SQ and one CQ between multiple threads(bound by >>>> the max number of CPU cores) for direct read/write access using very >>>> light mutex to sync. >>>> >>>> This also solves threads starvation issue - thread A submits the job >>>> into shared SQ while thread B both collects and _processes_ the result >>>> from the shared CQ instead of waiting on his own unique CQ for next >>>> completion event. >>>> >>> >>> >>> Well, if the SQ submitted by A and its matching CQ is consumed by B, and A will need access to that CQ because it is tightly coupled to state it owns exclusively(for example), or other reasons, then you’d still need to move that CQ from B back to A, or share it somehow, which seems expensive-is. >>> >>> It depends on what kind of roles your threads have though; I am personally very much against sharing state between threads unless there a really good reason for it. >>> >>> >>> >>> >>> >>> >>>> On Wed, May 13, 2020 at 2:56 PM Mark Papadakis >>>> wrote: >>>>> >>>>> For what it’s worth, I am (also) using using multiple “reactor” (i.e event driven) cores, each associated with one OS thread, and each reactor core manages its own io_uring context/queues. >>>>> >>>>> Even if scheduling all SQEs through a single io_uring SQ — by e.g collecting all such SQEs in every OS thread and then somehow “moving” them to the one OS thread that manages the SQ so that it can enqueue them all -- is very cheap, you ‘d still need to drain the CQ from that thread and presumably process those CQEs in a single OS thread, which will definitely be more work than having each reactor/OS thread dequeue CQEs for SQEs that itself submitted. >>>>> You could have a single OS thread just for I/O and all other threads could do something else but you’d presumably need to serialize access/share state between them and the one OS thread for I/O which maybe a scalability bottleneck. >>>>> >>>>> ( if you are curious, you can read about it here https://medium.com/@markpapadakis/building-high-performance-services-in-2020-e2dea272f6f6 ) >>>>> >>>>> If you experiment with the various possible designs though, I’d love it if you were to share your findings. >>>>> >>>>> — >>>>> @markpapapdakis >>>>> >>>>> >>>>>> On 13 May 2020, at 2:01 PM, Dmitry Sychov wrote: >>>>>> >>>>>> Hi Hielke, >>>>>> >>>>>>> If you want max performance, what you generally will see in non-blocking servers is one event loop per core/thread. >>>>>>> This means one ring per core/thread. Of course there is no simple answer to this. >>>>>>> See how thread-based servers work vs non-blocking servers. E.g. Apache vs Nginx or Tomcat vs Netty. >>>>>> >>>>>> I think a lot depends on the internal uring implementation. To what >>>>>> degree the kernel is able to handle multiple urings independently, >>>>>> without much congestion points(like updates of the same memory >>>>>> locations from multiple threads), thus taking advantage of one ring >>>>>> per CPU core. >>>>>> >>>>>> For example, if the tasks from multiple rings are later combined into >>>>>> single input kernel queue (effectively forming a congestion point) I >>>>>> see >>>>>> no reason to use exclusive ring per core in user space. >>>>>> >>>>>> [BTW in Windows IOCP is always one input+output queue for all(active) threads]. >>>>>> >>>>>> Also we could pop out multiple completion events from a single CQ at >>>>>> once to spread the handling to cores-bound threads . >>>>>> >>>>>> I thought about one uring per core at first, but now I'am not sure - >>>>>> maybe the kernel devs have something to add to the discussion? >>>>>> >>>>>> P.S. uring is the main reason I'am switching from windows to linux dev >>>>>> for client-sever app so I want to extract the max performance possible >>>>>> out of this new exciting uring stuff. :) >>>>>> >>>>>> Thanks, Dmitry >>>>> >>> -- Pavel Begunkov