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=-17.6 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 3706EC433F5 for ; Mon, 6 Sep 2021 17:41:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 214ED603E7 for ; Mon, 6 Sep 2021 17:41:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244167AbhIFRmE (ORCPT ); Mon, 6 Sep 2021 13:42:04 -0400 Received: from out30-130.freemail.mail.aliyun.com ([115.124.30.130]:48832 "EHLO out30-130.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244010AbhIFRmD (ORCPT ); Mon, 6 Sep 2021 13:42:03 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R191e4;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_---0UnW7BEi_1630950057; Received: from B-25KNML85-0107.local(mailfrom:haoxu@linux.alibaba.com fp:SMTPD_---0UnW7BEi_1630950057) by smtp.aliyun-inc.com(127.0.0.1); Tue, 07 Sep 2021 01:40:57 +0800 Subject: Re: [PATCH 4/6] io_uring: let fast poll support multishot To: Pavel Begunkov , Jens Axboe Cc: io-uring@vger.kernel.org, Joseph Qi References: <20210903110049.132958-1-haoxu@linux.alibaba.com> <20210903110049.132958-5-haoxu@linux.alibaba.com> From: Hao Xu Message-ID: <8f3046d9-d678-f755-e7af-a0e5040699ca@linux.alibaba.com> Date: Tue, 7 Sep 2021 01:40:57 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 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 2021/9/6 下午11:56, Pavel Begunkov 写道: > On 9/3/21 12:00 PM, Hao Xu wrote: >> For operations like accept, multishot is a useful feature, since we can >> reduce a number of accept sqe. Let's integrate it to fast poll, it may >> be good for other operations in the future. > > __io_arm_poll_handler() | > -> vfs_poll() | > | io_async_task_func() // post CQE > | ... > | do_apoll_rewait(); > -> continues after vfs_poll(),| > removing poll->head of | > the second poll attempt. | > > Sorry.. a little bit confused by this case, would you mind explain a bit more..is the right part a system-workqueue context? and is do_apoll_rewait() io_poll_rewait() function? > One of the reasons for forbidding multiple apoll's is that it > might be racy. I haven't looked into this implementation, but > we should check if there will be problems from that. > > FWIW, putting aside this patchset, the poll/apoll is not in > the best shape and can use some refactoring. > > >> Signed-off-by: Hao Xu >> --- >> fs/io_uring.c | 15 ++++++++++++--- >> 1 file changed, 12 insertions(+), 3 deletions(-) >> >> diff --git a/fs/io_uring.c b/fs/io_uring.c >> index d6df60c4cdb9..dae7044e0c24 100644 >> --- a/fs/io_uring.c >> +++ b/fs/io_uring.c >> @@ -5277,8 +5277,15 @@ static void io_async_task_func(struct io_kiocb *req, bool *locked) >> return; >> } >> >> - hash_del(&req->hash_node); >> - io_poll_remove_double(req); >> + if (READ_ONCE(apoll->poll.canceled)) >> + apoll->poll.events |= EPOLLONESHOT; >> + if (apoll->poll.events & EPOLLONESHOT) { >> + hash_del(&req->hash_node); >> + io_poll_remove_double(req); >> + } else { >> + add_wait_queue(apoll->poll.head, &apoll->poll.wait); >> + } >> + >> spin_unlock(&ctx->completion_lock); >> >> if (!READ_ONCE(apoll->poll.canceled)) >> @@ -5366,7 +5373,7 @@ static int io_arm_poll_handler(struct io_kiocb *req) >> struct io_ring_ctx *ctx = req->ctx; >> struct async_poll *apoll; >> struct io_poll_table ipt; >> - __poll_t ret, mask = EPOLLONESHOT | POLLERR | POLLPRI; >> + __poll_t ret, mask = POLLERR | POLLPRI; >> int rw; >> >> if (!req->file || !file_can_poll(req->file)) >> @@ -5388,6 +5395,8 @@ static int io_arm_poll_handler(struct io_kiocb *req) >> rw = WRITE; >> mask |= POLLOUT | POLLWRNORM; >> } >> + if (!(req->flags & REQ_F_APOLL_MULTISHOT)) >> + mask |= EPOLLONESHOT; >> >> /* if we can't nonblock try, then no point in arming a poll handler */ >> if (!io_file_supports_nowait(req, rw)) >> >