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=ham 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 97B67C433ED for ; Thu, 29 Apr 2021 22:10:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5D21A61461 for ; Thu, 29 Apr 2021 22:10:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229705AbhD2WLH (ORCPT ); Thu, 29 Apr 2021 18:11:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58140 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229672AbhD2WLG (ORCPT ); Thu, 29 Apr 2021 18:11:06 -0400 Received: from mail-wr1-x431.google.com (mail-wr1-x431.google.com [IPv6:2a00:1450:4864:20::431]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D099DC06138B for ; Thu, 29 Apr 2021 15:10:17 -0700 (PDT) Received: by mail-wr1-x431.google.com with SMTP id l2so16103601wrm.9 for ; Thu, 29 Apr 2021 15:10:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=l/VaDSXkUNTfWmr9Ex/9IPmov3LaljJD7+GwSEXe6WQ=; b=FqHNDSkZjGfBcEM79WewiIhA3R81AnYShOuEK9nWKH0bbBc56IC3iLwYWJ0yxFLFTK f/wu1Q1IrhdFPIBDn/8qD72Zm4z6eosC495MhTZK8FlgkxRlnZbbarO/OVsbTWIMXy95 32ToP+zbVSUq78XGcMrxExP9BJGE+80uI6W67qzvSfdwAI5SXoijpAr9oGWcmdqIo/bn 7icQbttGqjP4urUPRi/poMDECa+kjOF6/c5Mq3YPeUXnefKyn1a4OFuJk3AgXhr6vHG2 U5wtb5xvBD2OF1BWZFkDwiXc6NtNvjbcznGa7l7D3ZtXYW7taO7hRiNgCjoGpdWg1jpl XE9w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=l/VaDSXkUNTfWmr9Ex/9IPmov3LaljJD7+GwSEXe6WQ=; b=kkudrTZFlg5Rb5nI3GrfAoLDkrAqxuSL8WohHR43/EZ16hxXiqqwsD4Y4l7RsQgaFG QD8BEIrKqp/GhgpYSsQKeDcNz26gZURuvBjsYSbf17qkpOvBhtJ3X7T2aer1prCSpAap uN7npYfWcvFi8rLzCqA9bp049wZyJOllpmMFjloexk+28oei8IM0fZKPDRvaNQ4v2EhU ZBVzRYOksgcYwXZbtNxyVv63lUosVNVF4RuRkjO7ReZS+u6g32yzD/jVzK3/C6RlkfEn Mw80CXz5A4AVD1srBVeYEO4y6pcjUrF30OxsxbkNvd9+TFCLgDKijswQaZ8CB5mLIlX+ xt0w== X-Gm-Message-State: AOAM530U8x3ZB+POruSC59/ESdh3kOT1Ui/grQY8+GmiQay1GQCoRA2H Sc2hogdc/Q+XqE8IzDzgxRw= X-Google-Smtp-Source: ABdhPJxhk5VqjyjQZD27oZm1HH8eRZiUacqDy/icYeL337vnF/SuoBlMVRcj/T+hgXdiU7knV3K7PQ== X-Received: by 2002:a5d:6da8:: with SMTP id u8mr2266786wrs.48.1619734216632; Thu, 29 Apr 2021 15:10:16 -0700 (PDT) Received: from [192.168.8.197] ([148.252.132.80]) by smtp.gmail.com with ESMTPSA id i20sm11118451wmq.29.2021.04.29.15.10.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 29 Apr 2021 15:10:16 -0700 (PDT) Subject: Re: [PATCH RFC 5.13 2/2] io_uring: submit sqes in the original context when waking up sqthread To: Hao Xu , Jens Axboe Cc: io-uring@vger.kernel.org, Joseph Qi References: <1619616748-17149-1-git-send-email-haoxu@linux.alibaba.com> <1619616748-17149-3-git-send-email-haoxu@linux.alibaba.com> <571b5633-3286-feba-af6b-e388f52fc89b@gmail.com> <755e4e92-9ff2-9246-75c0-63fb79ae1646@linux.alibaba.com> From: Pavel Begunkov Message-ID: Date: Thu, 29 Apr 2021 23:10:12 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.0 MIME-Version: 1.0 In-Reply-To: <755e4e92-9ff2-9246-75c0-63fb79ae1646@linux.alibaba.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 4/29/21 9:44 AM, Hao Xu wrote: > 在 2021/4/28 下午10:34, Pavel Begunkov 写道: >> On 4/28/21 2:32 PM, Hao Xu wrote: >>> sqes are submitted by sqthread when it is leveraged, which means there >>> is IO latency when waking up sqthread. To wipe it out, submit limited >>> number of sqes in the original task context. >>> Tests result below: >> >> Frankly, it can be a nest of corner cases if not now then in the future, >> leading to a high maintenance burden. Hence, if we consider the change, >> I'd rather want to limit the userspace exposure, so it can be removed >> if needed. >> >> A noticeable change of behaviour here, as Hao recently asked, is that >> the ring can be passed to a task from a completely another thread group, >> and so the feature would execute from that context, not from the >> original/sqpoll one. >> >> Not sure IORING_ENTER_SQ_DEPUTY knob is needed, but at least can be >> ignored if the previous point is addressed. >> >>> >>> 99th latency: >>> iops\idle    10us    60us    110us    160us    210us    260us    310us    360us    410us    460us    510us >>> with this patch: >>> 2k          13    13    12    13    13    12    12    11    11    10.304    11.84 >>> without this patch: >>> 2k          15    14    15    15    15    14    15    14    14    13    11.84 >> >> Not sure the second nine describes it well enough, please can you >> add more data? Mean latency, 50%, 90%, 99%, 99.9%, t-put. >> >> Btw, how happened that only some of the numbers have fractional part? >> Can't believe they all but 3 were close enough to integer values. >> >>> fio config: >>> ./run_fio.sh >>> fio \ >>> --ioengine=io_uring --sqthread_poll=1 --hipri=1 --thread=1 --bs=4k \ >>> --direct=1 --rw=randread --time_based=1 --runtime=300 \ >>> --group_reporting=1 --filename=/dev/nvme1n1 --sqthread_poll_cpu=30 \ >>> --randrepeat=0 --cpus_allowed=35 --iodepth=128 --rate_iops=${1} \ >>> --io_sq_thread_idle=${2} >>> >>> Signed-off-by: Hao Xu >>> --- >>>   fs/io_uring.c                 | 29 +++++++++++++++++++++++------ >>>   include/uapi/linux/io_uring.h |  1 + >>>   2 files changed, 24 insertions(+), 6 deletions(-) >>> >>> diff --git a/fs/io_uring.c b/fs/io_uring.c >>> index 1871fad48412..f0a01232671e 100644 >>> --- a/fs/io_uring.c >>> +++ b/fs/io_uring.c >>> @@ -1252,7 +1252,12 @@ static void io_queue_async_work(struct io_kiocb *req) >>>   { >>>       struct io_ring_ctx *ctx = req->ctx; >>>       struct io_kiocb *link = io_prep_linked_timeout(req); >>> -    struct io_uring_task *tctx = req->task->io_uring; >>> +    struct io_uring_task *tctx = NULL; >>> + >>> +    if (ctx->sq_data && ctx->sq_data->thread) >>> +        tctx = ctx->sq_data->thread->io_uring; >> >> without park it's racy, sq_data->thread may become NULL and removed, >> as well as its ->io_uring. > I now think that it's ok to queue async work to req->task->io_uring. I > look through all the OPs, seems only have to take care of async_cancel: > > io_async_cancel(req) { >    cancel from req->task->io_uring; >    cancel from ctx->tctx_list > } > > Given req->task is 'original context', the req to be cancelled may in > ctx->sq_data->thread->io_uring's iowq. So search the req from > sqthread->io_uring is needed here. This avoids overload in main code > path. > Did I miss something else? It must be req->task->io_uring, otherwise cancellations will be broken. And using it should be fine in theory because io-wq/etc. should be set up by io_uring_add_task_file() One more problem to the pile is io_req_task_work_add() and notify mode it choses. Look for IORING_SETUP_SQPOLL in the function. Also, IOPOLL+SQPOLL io_uring_try_cancel_requests() looks like may fail (didn't double check it). Look again for IORING_SETUP_SQPOLL. I'd rather recommend to go over all uses of IORING_SETUP_SQPOLL and think whether it's flawed. > > >> >>> +    else >>> +        tctx = req->task->io_uring; >>>         BUG_ON(!tctx); >>>       BUG_ON(!tctx->io_wq); >> >> [snip] >> > -- Pavel Begunkov