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 80BE5C49361 for ; Sun, 20 Jun 2021 19:56:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 61F0F6112D for ; Sun, 20 Jun 2021 19:56:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230006AbhFTT6e (ORCPT ); Sun, 20 Jun 2021 15:58:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37822 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229872AbhFTT6d (ORCPT ); Sun, 20 Jun 2021 15:58:33 -0400 Received: from mail-wm1-x329.google.com (mail-wm1-x329.google.com [IPv6:2a00:1450:4864:20::329]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 376BCC061574; Sun, 20 Jun 2021 12:56:20 -0700 (PDT) Received: by mail-wm1-x329.google.com with SMTP id m3so9043277wms.4; Sun, 20 Jun 2021 12:56:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=to:references:from:subject:message-id:date:user-agent:mime-version :in-reply-to:content-language:content-transfer-encoding; bh=ZryyT0HWRM0dOmzL4ADJOpit6XxJrpxMO5spYCSH/pc=; b=ZEldtTJkgOZhfUXxFpr+1e+Rb/Fs37YtM7KDEAnelicz9v49PLa1Ca/O7ieidu/eF4 DIWTXjGijm5JtM7Z3e4kh9Q6qUy+3Fkh+oSZvka4xS8f441grSpb57BGWa0v4XsIcGK3 tlS1V/4oEaaXdlpIBuUB3RSM56mgMA4+SNd9WqpwoRNbbNT7/fL2VvYYUBF1DjfNo/2j 1mG0Po9Vkgu4OG6MI+kGyUEasRsVjWGIyDjm6Wh26zJrKbszUKCsrjwlayc1NBwkJ+Z6 M/b3qma6ITonSqZM7e3BXDgArpntU3rTpeGPz1iGYgod0tYO0DIJHbV8ZV15pNCJ29uz Qg4A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:to:references:from:subject:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=ZryyT0HWRM0dOmzL4ADJOpit6XxJrpxMO5spYCSH/pc=; b=AH5MUcYDBqraXH2iWfmryY6b+ck+i7bnp6fIl1E3ZaQh70t9w/rcgdr4Kv8BdRJU3x IgIYeXuoRu9+zr750KK8pKJvg+x7xHbl/72lCiQbvmHg+/M8DE/TClieYucxLgEvpK0g h+6YBeDr+4PVrIBKkhyo5UU4ek9nbTaecgZMMk22LNJWe7wLHJee+jlRF4czbIyTneYL 4V+QQcWglf31f/4bXmKcYHNhftg5Bie/S/QmujXLg9IgJkLIEkiL9b7Fn2S1J7LEXoXP 21FVW/lbyQbzAZKu3VYDNu8F9WnBPDdtICN/g7bV0PT2UPkMRV3qbNNl9IuRYg3c4Rs3 bv4Q== X-Gm-Message-State: AOAM531KLWNzOOT+3WVU3nmmWco+lGNoRTaglC3xVxtHiU3PdOIbmLuI PCJKk7NqxUfdsZ2jmbRU8FkFsSdEimPcLw== X-Google-Smtp-Source: ABdhPJzHDsNL+HrdWptOaWSkokuFrZcR1p/dUhCV+ZN1nkxKkKXrL74XLfpmDlYMrBrUZwcEQkhXvQ== X-Received: by 2002:a1c:43c3:: with SMTP id q186mr5697931wma.44.1624218978603; Sun, 20 Jun 2021 12:56:18 -0700 (PDT) Received: from [192.168.8.197] ([185.69.145.72]) by smtp.gmail.com with ESMTPSA id g17sm19679172wrh.72.2021.06.20.12.56.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 20 Jun 2021 12:56:18 -0700 (PDT) To: Olivier Langlois , Jens Axboe , io-uring@vger.kernel.org, linux-kernel@vger.kernel.org References: From: Pavel Begunkov Subject: Re: [PATCH v2] io_uring: reduce latency by reissueing the operation Message-ID: <61668060-6401-ccc0-06e8-29d6320b720a@gmail.com> Date: Sun, 20 Jun 2021 20:56:04 +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: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/20/21 8:05 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. > > Signed-off-by: Olivier Langlois > --- > fs/io_uring.c | 26 +++++++++++++++++--------- > 1 file changed, 17 insertions(+), 9 deletions(-) > > diff --git a/fs/io_uring.c b/fs/io_uring.c > index fa8794c61af7..6e037304429a 100644 > --- a/fs/io_uring.c > +++ b/fs/io_uring.c > @@ -5143,7 +5143,10 @@ static __poll_t __io_arm_poll_handler(struct io_kiocb *req, > return mask; > } > > -static bool io_arm_poll_handler(struct io_kiocb *req) > +#define IO_ARM_POLL_OK 0 > +#define IO_ARM_POLL_ERR 1 > +#define IO_ARM_POLL_READY 2 Please add a new line here. Can even be moved somewhere to the top, but it's a matter of taste. Also, how about to rename it to apoll? io_uring internal rw/send/recv polling is often abbreviated as such around io_uring.c IO_APOLL_OK and so on. > +static int io_arm_poll_handler(struct io_kiocb *req) > { > const struct io_op_def *def = &io_op_defs[req->opcode]; > struct io_ring_ctx *ctx = req->ctx; > @@ -5153,22 +5156,22 @@ static bool io_arm_poll_handler(struct io_kiocb *req) > int rw; > > if (!req->file || !file_can_poll(req->file)) > - return false; > + return IO_ARM_POLL_ERR; It's not really an error. Maybe IO_APOLL_ABORTED or so? > if (req->flags & REQ_F_POLLED) > - return false; > + return IO_ARM_POLL_ERR; > if (def->pollin) > rw = READ; > else if (def->pollout) > rw = WRITE; > else > - return false; > + return IO_ARM_POLL_ERR; > /* if we can't nonblock try, then no point in arming a poll handler */ > if (!io_file_supports_async(req, rw)) > - return false; > + return IO_ARM_POLL_ERR; > > apoll = kmalloc(sizeof(*apoll), GFP_ATOMIC); > if (unlikely(!apoll)) > - return false; > + return IO_ARM_POLL_ERR; > apoll->double_poll = NULL; > > req->flags |= REQ_F_POLLED; > @@ -5194,12 +5197,12 @@ static bool io_arm_poll_handler(struct io_kiocb *req) > if (ret || ipt.error) { > io_poll_remove_double(req); > spin_unlock_irq(&ctx->completion_lock); > - return false; > + return ret?IO_ARM_POLL_READY:IO_ARM_POLL_ERR; spaces would be great. > } > spin_unlock_irq(&ctx->completion_lock); > trace_io_uring_poll_arm(ctx, req->opcode, req->user_data, mask, > apoll->poll.events); > - return true; > + return IO_ARM_POLL_OK; > } > > static bool __io_poll_remove_one(struct io_kiocb *req, > @@ -6416,6 +6419,7 @@ 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); > > /* > @@ -6435,12 +6439,16 @@ 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_ARM_POLL_READY: > + goto issue_sqe; Checked assembly, the fast path looks ok (i.e. not affected). Also, a note, linked_timeout is handled correctly. > + case IO_ARM_POLL_ERR: > /* > * Queued up for async execution, worker will release > * submit reference when the iocb is actually submitted. > */ > io_queue_async_work(req); > + break; > } > } else { > io_req_complete_failed(req, ret); > -- Pavel Begunkov