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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5A00EC48BF9 for ; Wed, 15 Nov 2023 13:43:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343975AbjKONnB (ORCPT ); Wed, 15 Nov 2023 08:43:01 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56094 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343698AbjKONnA (ORCPT ); Wed, 15 Nov 2023 08:43:00 -0500 Received: from out30-98.freemail.mail.aliyun.com (out30-98.freemail.mail.aliyun.com [115.124.30.98]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B9CE29B for ; Wed, 15 Nov 2023 05:42:56 -0800 (PST) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R861e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045176;MF=cruzzhao@linux.alibaba.com;NM=1;PH=DS;RN=12;SR=0;TI=SMTPD_---0VwTBm8C_1700055733; Received: from 192.168.1.107(mailfrom:cruzzhao@linux.alibaba.com fp:SMTPD_---0VwTBm8C_1700055733) by smtp.aliyun-inc.com; Wed, 15 Nov 2023 21:42:54 +0800 Message-ID: <246dee1f-5e14-e075-13c7-ce876305cb54@linux.alibaba.com> Date: Wed, 15 Nov 2023 21:42:13 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 Subject: Re: [PATCH 3/4] sched/fair: introduce core_vruntime and core_min_vruntime To: Peter Zijlstra Cc: mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, joel@joelfernandes.org, linux-kernel@vger.kernel.org References: <20231115113341.13261-1-CruzZhao@linux.alibaba.com> <20231115113341.13261-4-CruzZhao@linux.alibaba.com> <20231115122027.GZ8262@noisy.programming.kicks-ass.net> From: cruzzhao Content-Language: en-US In-Reply-To: <20231115122027.GZ8262@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2023/11/15 下午8:20, Peter Zijlstra 写道: > On Wed, Nov 15, 2023 at 07:33:40PM +0800, Cruz Zhao wrote: >> To compare the priority of sched_entity from different cpus of a core, >> we introduce core_vruntime to struct sched_entity and core_min_vruntime >> to struct cfs_rq. >> >> cfs_rq->core->core_min_vruntime records the min vruntime of the cfs_rqs >> of the same task_group among the core, and se->core_vruntime is the >> vruntime relative to se->cfs_rq->core->core_min_vruntime. > > But that makes absolutely no sense. vruntime of different RQs can > advance at wildly different rates. Not to mention there's this random > offset between them. > > No, this cannot be. Force idle vruntime snapshot does the same thing, comparing sea->vruntime - cfs_rqa->min_vruntime_fi with seb->vruntime - cfs_rqb->min_vruntime_fi, while sea and seb may have wildly different rates. Actually, cfs_rq->core->core_min_vruntime does the same thing as cfs_rq->min_vruntime_fi, providing a baseline, but cfs_rq->core->core_min_vruntime is more accurate. I've tried to implement a fair enough mechanism of core_vruntime, but it's too complex because of the weight, and it costs a lot. So this is a compromise solution. BTW, is there any other solutions to solve this problem? Best, Cruz Zhao