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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6D552C433EF for ; Thu, 10 Mar 2022 01:36:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229744AbiCJBhn (ORCPT ); Wed, 9 Mar 2022 20:37:43 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48030 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232808AbiCJBhl (ORCPT ); Wed, 9 Mar 2022 20:37:41 -0500 Received: from mail-pl1-x62b.google.com (mail-pl1-x62b.google.com [IPv6:2607:f8b0:4864:20::62b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 21AEA1275EB for ; Wed, 9 Mar 2022 17:36:41 -0800 (PST) Received: by mail-pl1-x62b.google.com with SMTP id e2so3508450pls.10 for ; Wed, 09 Mar 2022 17:36:41 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20210112.gappssmtp.com; s=20210112; h=message-id:date:mime-version:user-agent:subject:content-language:to :references:from:in-reply-to:content-transfer-encoding; bh=Y8+ehtFJJiePMQxGafSfUqd1ycIQvjf/gQ1D9tm1yFs=; b=agfoIgmBDmcV7Rp+Xi7JB2oCh15Y2GRMVx0EaFpfXUTUee89aV77abIwXPwlzMbgYq aQ0Za6NIklpT9QU8ENQ66BSqRkpa+nLU6y3TYMO11unJBskt6z71z3cIt8FfmLnvk3En /80cUoZRkVX2O/phu2R5KoF/uyNhBVP+TpxKSMDKDU/GxaRNEyCiAtYgktO4fKRmqCxk fsvarIKIAX68kQdK/ZdFAp9rdM1zwVLM3mTz1Uf81q14Sf2MDjj3bMht2/+6rCf9A3LH S8I2rD5gdYXihHchRw6A1FzG3UA9rgkQ92OY+skN2392Ht0m1f6Wt3f3sb8bx6KTZibk IGrw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:references:from:in-reply-to :content-transfer-encoding; bh=Y8+ehtFJJiePMQxGafSfUqd1ycIQvjf/gQ1D9tm1yFs=; b=Sd/Nq2sJrOBaoq7iof8Mjk+5AvrZw822If65ItBfIX3MgxmnjbRIEulN2gQ1Fntl2v PPzZIcP7QxzleLHqZfhGITVrkqwOtkmpq1j87KfMhmK4w4vM9PyjaZfUnyaQUd39ldk3 IdVrSVivmB0149oaTZX2FnfsT7Yo+02umXxuwOR2f81ZHYL/k86N5ZPLUGFjLGilc2iB dXidUy5ZmmN5/649cvnXk82AJZkeb4nAnkfxZQVLrdvqr4oJwWLUptO8z3mjzO9hENJs 9jR3MWEoWs5BBT1DAmRlFXOBOCzOHloBXZfzFrtEoDwu0FSIZ58dClAzwAqYu9/1UK/Y LdPg== X-Gm-Message-State: AOAM533OKv6UIebwvrEs2JTGdA60x6CYUjylPBDMsdHLJJ2JVjY3HVSB WBTM01vBEUk8iVU2kOK9/uhvuprKmK1ww/Zr X-Google-Smtp-Source: ABdhPJxv/qAHPn7HUjAlcpTpJMb2i1cf6nlI+OcUCMv9A1/wJ3S/eNcr24mVABR6OVPf+d8pZg8jsw== X-Received: by 2002:a17:90a:19d2:b0:1be:d815:477f with SMTP id 18-20020a17090a19d200b001bed815477fmr2457469pjj.23.1646876200508; Wed, 09 Mar 2022 17:36:40 -0800 (PST) Received: from [192.168.1.100] ([198.8.77.157]) by smtp.gmail.com with ESMTPSA id z72-20020a627e4b000000b004f70cbcb06esm4328390pfc.49.2022.03.09.17.36.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 09 Mar 2022 17:36:40 -0800 (PST) Message-ID: Date: Wed, 9 Mar 2022 18:36:39 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:91.0) Gecko/20100101 Thunderbird/91.6.1 Subject: Re: Sending CQE to a different ring Content-Language: en-US To: Artyom Pavlov , io-uring@vger.kernel.org References: From: Jens Axboe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 3/9/22 4:49 PM, Artyom Pavlov wrote: > Greetings! > > A common approach for multi-threaded servers is to have a number of > threads equal to a number of cores and launch a separate ring in each > one. AFAIK currently if we want to send an event to a different ring, > we have to write-lock this ring, create SQE, and update the index > ring. Alternatively, we could use some kind of user-space message > passing. > > Such approaches are somewhat inefficient and I think it can be solved > elegantly by updating the io_uring_sqe type to allow accepting fd of a > ring to which CQE must be sent by kernel. It can be done by > introducing an IOSQE_ flag and using one of currently unused padding > u64s. > > Such feature could be useful for load balancing and message passing > between threads which would ride on top of io-uring, i.e. you could > send NOP with user_data pointing to a message payload. So what you want is a NOP with 'fd' set to the fd of another ring, and that nop posts a CQE on that other ring? I don't think we'd need IOSQE flags for that, we just need a NOP that supports that. I see a few ways of going about that: 1) Add a new 'NOP' that takes an fd, and validates that that fd is an io_uring instance. It can then grab the completion lock on that ring and post an empty CQE. 2) We add a FEAT flag saying NOP supports taking an 'fd' argument, where 'fd' is another ring. Posting CQE same as above. 3) We add a specific opcode for this. Basically the same as #2, but maybe with a more descriptive name than NOP. Might make sense to pair that with a CQE flag or something like that, as there's no specific user_data that could be used as it doesn't match an existing SQE that has been issued. IORING_CQE_F_WAKEUP for example. Would be applicable to all the above cases. I kind of like #3 the best. Add a IORING_OP_RING_WAKEUP command, require that sqe->fd point to a ring (could even be the ring itself, doesn't matter). And add IORING_CQE_F_WAKEUP as a specific flag for that. -- Jens Axboe