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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, 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 76DA8C433B4 for ; Thu, 29 Apr 2021 04:37:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 40E3260725 for ; Thu, 29 Apr 2021 04:37:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229746AbhD2Eht (ORCPT ); Thu, 29 Apr 2021 00:37:49 -0400 Received: from out30-44.freemail.mail.aliyun.com ([115.124.30.44]:50984 "EHLO out30-44.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229452AbhD2Eht (ORCPT ); Thu, 29 Apr 2021 00:37:49 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R141e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01424;MF=haoxu@linux.alibaba.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---0UX7aymG_1619671021; Received: from B-25KNML85-0107.local(mailfrom:haoxu@linux.alibaba.com fp:SMTPD_---0UX7aymG_1619671021) by smtp.aliyun-inc.com(127.0.0.1); Thu, 29 Apr 2021 12:37:01 +0800 Subject: Re: [PATCH RFC 5.13 2/2] io_uring: submit sqes in the original context when waking up sqthread To: Pavel Begunkov , 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> <6cc0020d-bfad-d723-6cc3-8bb2b8c4d313@gmail.com> From: Hao Xu Message-ID: Date: Thu, 29 Apr 2021 12:37:01 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.9.1 MIME-Version: 1.0 In-Reply-To: <6cc0020d-bfad-d723-6cc3-8bb2b8c4d313@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org 在 2021/4/28 下午10:37, Pavel Begunkov 写道: > On 4/28/21 3:34 PM, Pavel Begunkov wrote: >> 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. > > So maybe something like: > if (same_thread_group()) { > /* submit */ > }I thought this case(cross independent processes) for some time, Pavel, could you give more hints about how this may trigger errors? > >> >> Not sure IORING_ENTER_SQ_DEPUTY knob is needed, but at least can be >> ignored if the previous point is addressed. > > I'd question whether it'd be better with the flag or without doing > this feature by default. Just like what Jens said, the flag here is to allow users to do their decision, there may be cases like a application wants to offload as much as possible IO related work to sqpoll, so that it can be dedicated to computation work etc. > >> >>> >>> 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. Sure, I will. >> >> 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. This confused me a little bit too, but it is indeed what fio outputs. >> >>> 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. >> >>> + else >>> + tctx = req->task->io_uring; >>> >>> BUG_ON(!tctx); >>> BUG_ON(!tctx->io_wq); >> >> [snip] >> >