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=-15.5 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, 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 020FCC4338F for ; Sat, 24 Jul 2021 04:48:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CE83C60E98 for ; Sat, 24 Jul 2021 04:48:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229586AbhGXEIF (ORCPT ); Sat, 24 Jul 2021 00:08:05 -0400 Received: from out30-42.freemail.mail.aliyun.com ([115.124.30.42]:41146 "EHLO out30-42.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229550AbhGXEID (ORCPT ); Sat, 24 Jul 2021 00:08:03 -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=e01e04395;MF=haoxu@linux.alibaba.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---0UgmABnm_1627102113; Received: from B-25KNML85-0107.local(mailfrom:haoxu@linux.alibaba.com fp:SMTPD_---0UgmABnm_1627102113) by smtp.aliyun-inc.com(127.0.0.1); Sat, 24 Jul 2021 12:48:34 +0800 Subject: Re: [PATCH io_uring-5.14 v2] io_uring: remove double poll wait entry for pure poll To: Pavel Begunkov , Jens Axboe Cc: io-uring@vger.kernel.org, Joseph Qi References: <20210723092227.137526-1-haoxu@linux.alibaba.com> From: Hao Xu Message-ID: <824dcbe0-34da-a075-12eb-ce7529f3e3f7@linux.alibaba.com> Date: Sat, 24 Jul 2021 12:48:33 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.10.2 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 2021/7/23 下午10:31, Pavel Begunkov 写道: > On 7/23/21 10:22 AM, Hao Xu wrote: >> For pure poll requests, we should remove the double poll wait entry. >> And io_poll_remove_double() is good enough for it compared with >> io_poll_remove_waitqs(). > > 5.14 in the subject hints me that it's a fix. Is it? > Can you add what it fixes or expand on why it's better? Hi Pavel, I found that for poll_add() requests, it doesn't remove the double poll wait entry when it's done, neither after vfs_poll() or in the poll completion handler. The patch is mainly to fix it. > > >> Signed-off-by: Hao Xu >> --- >> >> v1-->v2 >> delete redundant io_poll_remove_double() >> >> fs/io_uring.c | 5 ++--- >> 1 file changed, 2 insertions(+), 3 deletions(-) >> >> diff --git a/fs/io_uring.c b/fs/io_uring.c >> index f2fe4eca150b..c5fe8b9e26b4 100644 >> --- a/fs/io_uring.c >> +++ b/fs/io_uring.c >> @@ -4903,7 +4903,6 @@ static bool io_poll_complete(struct io_kiocb *req, __poll_t mask) >> if (req->poll.events & EPOLLONESHOT) >> flags = 0; >> if (!io_cqring_fill_event(ctx, req->user_data, error, flags)) { >> - io_poll_remove_waitqs(req); Currently I only see it does that with io_poll_remove_waitqs() when cqring overflow and then ocqe allocation failed. Using io_poll_remove_waitqs() here is not very suitable since (1) it calls __io_poll_remove_one() which set poll->cancelled = true, why do we set poll->cancelled and poll->done to true at the same time though I think that doesn't cause any problem. (2) it does list_del_init(&poll->wait.entry) and hash_del(&req->hash_node) which has been already done. Correct me if I'm wrong since I may misunderstand the code. Regards, Hao >> req->poll.done = true; >> flags = 0; >> } >> @@ -4926,6 +4925,7 @@ static void io_poll_task_func(struct io_kiocb *req) >> >> done = io_poll_complete(req, req->result); >> if (done) { >> + io_poll_remove_double(req); >> hash_del(&req->hash_node); >> } else { >> req->result = 0; >> @@ -5113,7 +5113,7 @@ static __poll_t __io_arm_poll_handler(struct io_kiocb *req, >> ipt->error = -EINVAL; >> >> spin_lock_irq(&ctx->completion_lock); >> - if (ipt->error) >> + if (ipt->error || (mask && (poll->events & EPOLLONESHOT))) >> io_poll_remove_double(req); >> if (likely(poll->head)) { >> spin_lock(&poll->head->lock); >> @@ -5185,7 +5185,6 @@ static int io_arm_poll_handler(struct io_kiocb *req) >> ret = __io_arm_poll_handler(req, &apoll->poll, &ipt, mask, >> io_async_wake); >> if (ret || ipt.error) { >> - io_poll_remove_double(req); >> spin_unlock_irq(&ctx->completion_lock); >> if (ret) >> return IO_APOLL_READY; >> >