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=-11.1 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,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 9D84CC433EF for ; Fri, 3 Sep 2021 15:04:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 82534610CF for ; Fri, 3 Sep 2021 15:04:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229789AbhICPFK (ORCPT ); Fri, 3 Sep 2021 11:05:10 -0400 Received: from out30-45.freemail.mail.aliyun.com ([115.124.30.45]:49378 "EHLO out30-45.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229997AbhICPFK (ORCPT ); Fri, 3 Sep 2021 11:05:10 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R281e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04394;MF=haoxu@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0Un7GxII_1630681447; Received: from B-25KNML85-0107.local(mailfrom:haoxu@linux.alibaba.com fp:SMTPD_---0Un7GxII_1630681447) by smtp.aliyun-inc.com(127.0.0.1); Fri, 03 Sep 2021 23:04:07 +0800 Subject: Re: [PATCH 2/2] io_uring: consider cgroup setting when binding sqpoll cpu To: Tejun Heo Cc: Jens Axboe , Zefan Li , Johannes Weiner , Pavel Begunkov , io-uring@vger.kernel.org, cgroups@vger.kernel.org, Joseph Qi References: <20210901124322.164238-1-haoxu@linux.alibaba.com> <20210901124322.164238-3-haoxu@linux.alibaba.com> From: Hao Xu Message-ID: Date: Fri, 3 Sep 2021 23:04:07 +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 2021/9/2 上午12:41, Tejun Heo 写道: Hi Tejun, > Hello, > > On Wed, Sep 01, 2021 at 08:43:22PM +0800, Hao Xu wrote: >> @@ -7112,11 +7113,9 @@ static int io_sq_thread(void *data) >> >> snprintf(buf, sizeof(buf), "iou-sqp-%d", sqd->task_pid); >> set_task_comm(current, buf); >> + if (sqd->sq_cpu != -1 && test_cpu_in_current_cpuset(sqd->sq_cpu)) >> set_cpus_allowed_ptr(current, cpumask_of(sqd->sq_cpu)); >> + > > Would it make sense to just test whether set_cpus_allowed_ptr() succeeded > afterwards? Do you mean: if (sqd->sq_cpu != -1 && !set_cpus_allowed_ptr(current, cpumask_of(sqd->sq_cpu))) I'm not familiar with set_cpus_allowed_ptr(), you mean it contains the similar logic of test_cpu_in_current_cpuset? > >> @@ -8310,8 +8309,10 @@ static int io_sq_offload_create(struct io_ring_ctx *ctx, >> int cpu = p->sq_thread_cpu; >> >> ret = -EINVAL; >> - if (cpu >= nr_cpu_ids || !cpu_online(cpu)) >> + if (cpu >= nr_cpu_ids || !cpu_online(cpu) || >> + !test_cpu_in_current_cpuset(cpu)) >> goto err_sqpoll; >> + > > Failing operations on transient conditions like this may be confusing. Let's > ignore cpuset for now. CPU hotplug is sometimes driven automatically for > power saving purposes, so failing operation based on whether a cpu is online > means that the success or failure of the operation can seem arbitrary. If > the operation takes place while the cpu happens to be online, it succeeds > and the thread gets unbound and rebound automatically as the cpu goes This is a bit beyond of my knowledge, so you mean if the cpu back online, the task will automatically schedule to this cpu? if it's true, I think the code logic here is fine. > offline and online. If the operation takes place while the cpu happens to be > offline, the operation fails. It's ok that it fails, we leave the option of retry to users themselves. > > I don't know what the intended behavior here should be and we haven't been > pretty bad at defining reasonable behavior around cpu hotplug, so it'd > probably be worthwhile to consider what the behavior should be. > > Thanks. > Thanks, Hao