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=-2.2 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, 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 5D0E3C432C1 for ; Tue, 24 Sep 2019 08:28:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 324E920872 for ; Tue, 24 Sep 2019 08:28:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=kernel-dk.20150623.gappssmtp.com header.i=@kernel-dk.20150623.gappssmtp.com header.b="BoVWD9Ei" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2394971AbfIXI2G (ORCPT ); Tue, 24 Sep 2019 04:28:06 -0400 Received: from mail-io1-f66.google.com ([209.85.166.66]:39983 "EHLO mail-io1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2394923AbfIXI2G (ORCPT ); Tue, 24 Sep 2019 04:28:06 -0400 Received: by mail-io1-f66.google.com with SMTP id h144so2353823iof.7 for ; Tue, 24 Sep 2019 01:28:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:from:to:cc:references:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=rN+CCFgjkVKfpkBu9it69/0SwXM97JRpAOcW4kIpzI4=; b=BoVWD9Ei+4upFvzInWl+wWNqH3L3WMLBfNPHPRYnQWHtbHJmNphgq8YocFrVqAHtRf R6iasukQHA7sVYsd14LhpbF1bLPMqNSx4PjGlM6+BdHreaTsrQbO4POGb59vvQSqHyp7 PkYbG0WOwey19zr/4wbS3P12SXf795gVfhBRBt8ybvn2/A55bMAsl2TUE3ek1dfEL1tK oLDqmJQ85s6iD0XldWvWOITuom9MWG2wKWk0WcS5PmB3pbHyQIbFi6hFk4XhWU/bpCct 89HbWNrY+euZgQlCzL+Y0/yua1XW/pXosymxcCEKH7psIboyrN7rfZtHw9xpT7vggfQw yGxw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:from:to:cc:references:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=rN+CCFgjkVKfpkBu9it69/0SwXM97JRpAOcW4kIpzI4=; b=dgZcq1vp1oh1tocvn+KVMAg6Aj7L+8IATm+S14DWYL9aCbwtastuLSi0vrKJ4LIXjc 654jeDRXj41qZsBkzuerTACqwuJeRse1r+LLiwFv2Dans8Pru0abY1j6A5hzD8ivp+V4 o3y7YxjqIBmxvAPq8aOUYSgWAIFaIjBFsSMVMWZ/hvkSeC8PFOKQiFo6I/B5v/eY8Xtv SggAt9dYSJ1/fCbW6i3D1uDetmIYsIlpQ1DbrcjjNISUOegdn1a3jP2a8uo+lpcvt07H Z9nYTvz4BAjHe8SIGvTMGTj3bGL/kUE1F/SqUj5CKa79g2AopdUnbFEEp8LYAu3UwK+l +2pQ== X-Gm-Message-State: APjAAAWhphYF5V8SKuLi352RirwQRqj/gAKjsEuMa1jVwsD3P4kcbPht YnggGSZzjqb/7d8yAvcObLXv8Eed6ctn9g== X-Google-Smtp-Source: APXvYqxi662Z4Bn70WGfxOYR9BgahyryS+CkPCnD//1DLNnyE5xB+ZdcX0sUI4SNFIDJbJgCaRINWA== X-Received: by 2002:a02:b60f:: with SMTP id h15mr2481697jam.73.1569313683084; Tue, 24 Sep 2019 01:28:03 -0700 (PDT) Received: from [172.19.131.113] ([8.46.75.9]) by smtp.gmail.com with ESMTPSA id g8sm914450ioc.0.2019.09.24.01.27.54 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 24 Sep 2019 01:28:02 -0700 (PDT) Subject: Re: [PATCH v2 0/2] Optimise io_uring completion waiting From: Jens Axboe To: Pavel Begunkov , Ingo Molnar Cc: Ingo Molnar , Peter Zijlstra , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org References: <20190923083549.GA42487@gmail.com> <731b2087-7786-5374-68ff-8cba42f0cd68@kernel.dk> <759b9b48-1de3-1d43-3e39-9c530bfffaa0@kernel.dk> <43244626-9cfd-0c0b-e7a1-878363712ef3@gmail.com> Message-ID: Date: Tue, 24 Sep 2019 10:27:47 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/24/19 2:02 AM, Jens Axboe wrote: > On 9/24/19 1:06 AM, Pavel Begunkov wrote: >> On 24/09/2019 02:00, Jens Axboe wrote: >>>> I think we can do the same thing, just wrapping the waitqueue in a >>>> structure with a count in it, on the stack. Got some flight time >>>> coming up later today, let me try and cook up a patch. >>> >>> Totally untested, and sent out 5 min before departure... But something >>> like this. >> Hmm, reminds me my first version. Basically that's the same thing but >> with macroses inlined. I wanted to make it reusable and self-contained, >> though. >> >> If you don't think it could be useful in other places, sure, we could do >> something like that. Is that so? > > I totally agree it could be useful in other places. Maybe formalized and > used with wake_up_nr() instead of adding a new primitive? Haven't looked > into that, I may be talking nonsense. > > In any case, I did get a chance to test it and it works for me. Here's > the "finished" version, slightly cleaned up and with a comment added > for good measure. Notes: This version gets the ordering right, you need exclusive waits to get fifo ordering on the waitqueue. Both versions (yours and mine) suffer from the problem of potentially waking too many. I don't think this is a real issue, as generally we don't do threaded access to the io_urings. But if you had the following tasks wait on the cqring: [min_events = 32], [min_events = 8], [min_events = 8] and we reach the io_cqring_events() == threshold, we'll wake all three. I don't see a good solution to this, so I suspect we just live with until proven an issue. Both versions are much better than what we have now. -- Jens Axboe