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 E76CAC433B4 for ; Wed, 5 May 2021 13:10:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BBF52613BF for ; Wed, 5 May 2021 13:10:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232395AbhEENLG (ORCPT ); Wed, 5 May 2021 09:11:06 -0400 Received: from out30-44.freemail.mail.aliyun.com ([115.124.30.44]:47278 "EHLO out30-44.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230208AbhEENLF (ORCPT ); Wed, 5 May 2021 09:11:05 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R501e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04395;MF=haoxu@linux.alibaba.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---0UXoW-dX_1620220207; Received: from B-25KNML85-0107.local(mailfrom:haoxu@linux.alibaba.com fp:SMTPD_---0UXoW-dX_1620220207) by smtp.aliyun-inc.com(127.0.0.1); Wed, 05 May 2021 21:10:08 +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> <755e4e92-9ff2-9246-75c0-63fb79ae1646@linux.alibaba.com> From: Hao Xu Message-ID: <06927a9b-42ad-61ef-1f6a-fe54011d05c4@linux.alibaba.com> Date: Wed, 5 May 2021 21:10:07 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.10.0 MIME-Version: 1.0 In-Reply-To: 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 2021/4/30 上午6:10, Pavel Begunkov 写道: > 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. How about: notify = TWA_SIGNAL if ( (is sq mode) and (sqd->thread == NULL or == req->task)) notify = TWA_NONE; > > Also, IOPOLL+SQPOLL io_uring_try_cancel_requests() looks like > may fail (didn't double check it). Look again for IORING_SETUP_SQPOLL. > I've excluded IOPOLL. This change will only affect SQPOLL mode. > I'd rather recommend to go over all uses of IORING_SETUP_SQPOLL > and think whether it's flawed. I'm working on this. (no obvious problem through eyes, will put the code change on more tests) > >> >> >>> >>>> +    else >>>> +        tctx = req->task->io_uring; >>>>         BUG_ON(!tctx); >>>>       BUG_ON(!tctx->io_wq); >>> >>> [snip] >>> >> >