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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_SANE_1 autolearn=no 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 CB957C433ED for ; Thu, 6 May 2021 19:20:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A1E2D61289 for ; Thu, 6 May 2021 19:20:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233064AbhEFTVZ (ORCPT ); Thu, 6 May 2021 15:21:25 -0400 Received: from out30-54.freemail.mail.aliyun.com ([115.124.30.54]:43672 "EHLO out30-54.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230375AbhEFTVY (ORCPT ); Thu, 6 May 2021 15:21:24 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R631e4;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=4;SR=0;TI=SMTPD_---0UY-T64p_1620328824; Received: from B-25KNML85-0107.local(mailfrom:haoxu@linux.alibaba.com fp:SMTPD_---0UY-T64p_1620328824) by smtp.aliyun-inc.com(127.0.0.1); Fri, 07 May 2021 03:20:24 +0800 Subject: Re: [PATCH RFC 5.13] io_uring: add IORING_REGISTER_PRIORITY To: Jens Axboe Cc: io-uring@vger.kernel.org, Pavel Begunkov , Joseph Qi References: <1620311593-46083-1-git-send-email-haoxu@linux.alibaba.com> <38e587bb-a484-24dc-1ea9-cc252b1639ba@kernel.dk> From: Hao Xu Message-ID: <92da0bd6-3de9-eedd-fca7-87d8ad99ba70@linux.alibaba.com> Date: Fri, 7 May 2021 03:20:24 +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: <38e587bb-a484-24dc-1ea9-cc252b1639ba@kernel.dk> 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 2021/5/7 上午1:10, Jens Axboe 写道: > On 5/6/21 8:33 AM, Hao Xu wrote: >> Users may want a higher priority for sq_thread or io-worker. Provide a >> way to change the nice value(for SCHED_NORMAL) or scheduling policy. > > Silly question - why is this needed for sqpoll? With the threads now > being essentially user threads, why can't we just modify nice and > scheduler class from userspace instead? That should work now. I think > this is especially true for sqpoll where it's persistent, and argument > could be made for the io-wq worker threads that we'd need io_uring > support for that, as they come and go and there's no reliable way to > find and tweak the thread scheduler settings for that particular use > case. > > It may be more convenient to support this through io_uring, and that is > a valid argument. I do think that the better way would then be to simply > pass back the sqpoll pid after ring setup, because then it'd almost be > as simple to do it from the app itself using the regular system call > interfaces for that. > Hi Jens, It's my bad. I didn't realize this until I almost completed the patch, then I looked into io_uring_param, found just __u32 resv[3] can be leveraged. Not sure if it's neccessary to occupy one to do this, so I still sent this patch for comments. > In summary, I do think this _may_ make sense for the worker threads, > being able to pass in this information and have io-wq worker thread > setup perform the necessary tweaks when a thread is created, but it does I'm working on this(for the io-wq worker), have done part of it. > seem a bit silly to add this for sqpoll where it could just as easily be > achieved from the application itself without needing to add this It's beyond my knowledge, correct me if I'm wrong: if we do it from application, we have to search the pid of sq_thread by it's name which is iou-sqp-`sqd->task_pid`, and may be cut off because of TASK_COMM_LEN(would this macro value be possibly changed in the future?). And set_task_comm() is called when sq_thread runs, so there is very small chance(but there is) that set_task_comm() hasn't been called when application try to get the command name of sq_thread. Based on this (if it is not wrong...) I think return pid of sq_thread in io_uring level may be a better choice. Regards, Hao > support. > > What do you think? >