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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,UNPARSEABLE_RELAY 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 87D0CC43142 for ; Tue, 31 Jul 2018 14:59:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D3A5220870 for ; Tue, 31 Jul 2018 14:59:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D3A5220870 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732486AbeGaQkK (ORCPT ); Tue, 31 Jul 2018 12:40:10 -0400 Received: from out30-130.freemail.mail.aliyun.com ([115.124.30.130]:57640 "EHLO out30-130.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732268AbeGaQkK (ORCPT ); Tue, 31 Jul 2018 12:40:10 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R151e4;CH=green;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e07488;MF=xlpang@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0T5iG5K3_1533049129; Received: from xunleideMacBook-Pro.local(mailfrom:xlpang@linux.alibaba.com fp:SMTPD_---0T5iG5K3_1533049129) by smtp.aliyun-inc.com(127.0.0.1); Tue, 31 Jul 2018 22:58:49 +0800 Reply-To: xlpang@linux.alibaba.com Subject: Re: [PATCH] sched/fair: sync expires_seq in distribute_cfs_runtime() To: Cong Wang Cc: LKML , Ben Segall , Linus Torvalds , Peter Zijlstra , Thomas Gleixner References: <20180728002409.5781-1-xiyou.wangcong@gmail.com> From: Xunlei Pang Message-ID: Date: Tue, 31 Jul 2018 22:58:49 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/31/18 1:55 AM, Cong Wang wrote: > On Sun, Jul 29, 2018 at 10:29 PM Xunlei Pang wrote: >> >> Hi Cong, >> >> On 7/28/18 8:24 AM, Cong Wang wrote: >>> Each time we sync cfs_rq->runtime_expires with cfs_b->runtime_expires, >>> we should sync its ->expires_seq too. However it is missing >>> for distribute_cfs_runtime(), especially the slack timer call path. >> >> I don't think it's a problem, as expires_seq will get synced in >> assign_cfs_rq_runtime(). > > Sure, but there is a small window during which they are not synced. > Why do you want to wait until the next assign_cfs_rq_runtime() when > you already know runtime_expires is synced? > > Also, expire_cfs_rq_runtime() is called before assign_cfs_rq_runtime() > inside __account_cfs_rq_runtime(), which means the check of > cfs_rq->expires_seq is not accurate for unthrottling case if the clock > drift happens soon enough? > expire_cfs_rq_runtime(): if (cfs_rq->expires_seq == cfs_b->expires_seq) { /* extend local deadline, drift is bounded above by 2 ticks */ cfs_rq->runtime_expires += TICK_NSEC; } else { /* global deadline is ahead, expiration has passed */ cfs_rq->runtime_remaining = 0; } So if clock drift happens soon, then expires_seq decides the correct thing we should do: if cfs_b->expires_seq advanced, then clear the stale cfs_rq->runtime_remaining from the slack timer of the past period, then assign_cfs_rq_runtime() will refresh them afterwards, otherwise it is a real clock drift. I am still not getting where the race is?