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=-14.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable 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 756DDC48BE5 for ; Tue, 22 Jun 2021 17:55:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 57A3F611CE for ; Tue, 22 Jun 2021 17:55:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232391AbhFVR5Y (ORCPT ); Tue, 22 Jun 2021 13:57:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36916 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229501AbhFVR5W (ORCPT ); Tue, 22 Jun 2021 13:57:22 -0400 Received: from mail-ej1-x62d.google.com (mail-ej1-x62d.google.com [IPv6:2a00:1450:4864:20::62d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 225FCC061574; Tue, 22 Jun 2021 10:55:05 -0700 (PDT) Received: by mail-ej1-x62d.google.com with SMTP id nd37so35891332ejc.3; Tue, 22 Jun 2021 10:55:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:references:from:message-id:date:user-agent:mime-version :in-reply-to:content-language:content-transfer-encoding; bh=KSXjx7PRiNt3XduVl93AmUJtxfhvnhuoaCB1HZWKmnc=; b=Bidbwj3CGzT5t2FWODJvbz2Y8P1Rupv5wK/arJZzZo9pgBxdFp53tchPoJ6GK3OgBC nyrcJGpuKeKNo9+t6HM0hLuPTyvBsafFwXIX6OkbcJwmRf3m7aKVDfDb8NVAxLQwt7Tq 5gF+E0AFoJ9dVuzE6AGwQxjxBw0QdD779zz+T5ZhKLUhaD2FJljhY6tcQrhgo4gu/pUL AJDOPnL3rCvP8ja4ic2tkY127pXYlEIR+dxRqJfmVx4FzlExW8k/qhHcFVYfL1Z1iR3G 8NqsVaI1ViliSE6//WBsmcupoBlmDj1HhvM+7HfXGUC4DQh422nG+pltVGaOYkmU8TT/ vB+g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=KSXjx7PRiNt3XduVl93AmUJtxfhvnhuoaCB1HZWKmnc=; b=m+DDkU+mCd38foSEGOXpK3E6hw2EftpF87cdIwEihSMW0VSi+I4BQFv+wPkyqmvkh3 NjB7LNdgBbpt1t8GomyHEIo4pamWuHxBpj0wVyR1YqtQZ5lYts3+gcAy8WEjJ2Ajm8pO Iv7NxeIo2iLVbqMCw1iPRnwokc0p/sDJZvLp56XzKr/ZsoCB3ZYkryhKTzF0dr+QqXqe Le4fPwCtOApKRriwBEdDc3Tuj+3H0sJXnhfVbo64eL+eeaNLFxtkQD//SPE8/feDtCvI wH+C2MB8ZL2cDWws8Ikol1qOaWARSZTeMlVeNRCBA8wf2A3G7uRYZKSrmxPM38atnlxA R1MQ== X-Gm-Message-State: AOAM531rkt9/IGxEHpuAOzJs7xQ8Ix9t/EHDRYyYMPj+VvT5HKvH1HJo kbhhNkyZPU7XRqPvcfJNUeWtoXgWKwcfg37w X-Google-Smtp-Source: ABdhPJwquXT4sEhi2ldQxEu0urYrUs6HA3bcnq+Dd4KHDJkSLjr+dDdF19cqg3fylWYudAW8ZugFhg== X-Received: by 2002:a17:907:d03:: with SMTP id gn3mr5378466ejc.516.1624384499159; Tue, 22 Jun 2021 10:54:59 -0700 (PDT) Received: from ?IPv6:2620:10d:c096:310::2410? ([2620:10d:c093:600::2:9d6e]) by smtp.gmail.com with ESMTPSA id w2sm6283394ejn.118.2021.06.22.10.54.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 22 Jun 2021 10:54:58 -0700 (PDT) Subject: Re: [PATCH v4] io_uring: reduce latency by reissueing the operation To: Olivier Langlois , Jens Axboe , io-uring@vger.kernel.org, linux-kernel@vger.kernel.org References: <9e8441419bb1b8f3c3fcc607b2713efecdef2136.1624364038.git.olivier@trillion01.com> From: Pavel Begunkov Message-ID: <678deb93-c4a5-5a14-9687-9e44f0f00b5a@gmail.com> Date: Tue, 22 Jun 2021 18:54:45 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <9e8441419bb1b8f3c3fcc607b2713efecdef2136.1624364038.git.olivier@trillion01.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/22/21 1:17 PM, Olivier Langlois wrote: > It is quite frequent that when an operation fails and returns EAGAIN, > the data becomes available between that failure and the call to > vfs_poll() done by io_arm_poll_handler(). > > Detecting the situation and reissuing the operation is much faster > than going ahead and push the operation to the io-wq. > > Performance improvement testing has been performed with: > Single thread, 1 TCP connection receiving a 5 Mbps stream, no sqpoll. > > 4 measurements have been taken: > 1. The time it takes to process a read request when data is already available > 2. The time it takes to process by calling twice io_issue_sqe() after vfs_poll() indicated that data was available > 3. The time it takes to execute io_queue_async_work() > 4. The time it takes to complete a read request asynchronously > > 2.25% of all the read operations did use the new path. > > ready data (baseline) > avg 3657.94182918628 > min 580 > max 20098 > stddev 1213.15975908162 > > reissue completion > average 7882.67567567568 > min 2316 > max 28811 > stddev 1982.79172973284 > > insert io-wq time > average 8983.82276995305 > min 3324 > max 87816 > stddev 2551.60056552038 > > async time completion > average 24670.4758861127 > min 10758 > max 102612 > stddev 3483.92416873804 > > Conclusion: > On average reissuing the sqe with the patch code is 1.1uSec faster and > in the worse case scenario 59uSec faster than placing the request on > io-wq > > On average completion time by reissuing the sqe with the patch code is > 16.79uSec faster and in the worse case scenario 73.8uSec faster than > async completion. > > Signed-off-by: Olivier Langlois > --- > fs/io_uring.c | 31 ++++++++++++++++++++++--------- > 1 file changed, 22 insertions(+), 9 deletions(-) > > diff --git a/fs/io_uring.c b/fs/io_uring.c > index fc8637f591a6..5efa67c2f974 100644 > --- a/fs/io_uring.c > +++ b/fs/io_uring.c [...] > static bool __io_poll_remove_one(struct io_kiocb *req, > @@ -6437,6 +6445,7 @@ static void __io_queue_sqe(struct io_kiocb *req) > struct io_kiocb *linked_timeout = io_prep_linked_timeout(req); > int ret; > > +issue_sqe: > ret = io_issue_sqe(req, IO_URING_F_NONBLOCK|IO_URING_F_COMPLETE_DEFER); > > /* > @@ -6456,12 +6465,16 @@ static void __io_queue_sqe(struct io_kiocb *req) > io_put_req(req); > } > } else if (ret == -EAGAIN && !(req->flags & REQ_F_NOWAIT)) { > - if (!io_arm_poll_handler(req)) { > + switch (io_arm_poll_handler(req)) { > + case IO_APOLL_READY: > + goto issue_sqe; > + case IO_APOLL_ABORTED: > /* > * Queued up for async execution, worker will release > * submit reference when the iocb is actually submitted. > */ > io_queue_async_work(req); > + break; Hmm, why there is a new break here? It will miscount @linked_timeout if you do that. Every io_prep_linked_timeout() should be matched with io_queue_linked_timeout(). > } > } else { > io_req_complete_failed(req, ret); > -- Pavel Begunkov