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 DC31BC4332F for ; Tue, 31 Oct 2023 15:52:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345124AbjJaPwa (ORCPT ); Tue, 31 Oct 2023 11:52:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47306 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231131AbjJaPw3 (ORCPT ); Tue, 31 Oct 2023 11:52:29 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id B8D48DF for ; Tue, 31 Oct 2023 08:52:26 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 02DA42F; Tue, 31 Oct 2023 08:53:08 -0700 (PDT) Received: from [192.168.178.6] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9F3073F67D; Tue, 31 Oct 2023 08:52:24 -0700 (PDT) Message-ID: Date: Tue, 31 Oct 2023 16:52:23 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 1/6] sched/uclamp: Track uclamped util_avg in sched_avg Content-Language: en-US To: Hongyan Xia , Ingo Molnar , Peter Zijlstra , Vincent Guittot , Juri Lelli Cc: Qais Yousef , Morten Rasmussen , Lukasz Luba , Christian Loehle , linux-kernel@vger.kernel.org References: <5564fc23d5e6425d069c36b4cef48edbe77fe64d.1696345700.git.Hongyan.Xia2@arm.com> From: Dietmar Eggemann In-Reply-To: <5564fc23d5e6425d069c36b4cef48edbe77fe64d.1696345700.git.Hongyan.Xia2@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/10/2023 11:04, Hongyan Xia wrote: > From: Hongyan Xia [...] > @@ -6445,6 +6450,21 @@ static int sched_idle_cpu(int cpu) > } > #endif > > +void ___update_util_avg_uclamp(struct sched_avg *avg, struct sched_entity *se); IMHO, `struct sched_avg *avg` can only be the one of a cfs_rq. So passing a cfs_rq would eliminate the question whether this can be from another se. > +static void update_se_chain(struct task_struct *p) > +{ > +#ifdef CONFIG_UCLAMP_TASK > + struct sched_entity *se = &p->se; > + struct rq *rq = task_rq(p); > + > + for_each_sched_entity(se) { > + struct cfs_rq *cfs_rq = cfs_rq_of(se); > + > + ___update_util_avg_uclamp(&cfs_rq->avg, se); > + } > +#endif > +} > /* > * The enqueue_task method is called before nr_running is > * increased. Here we update the fair scheduling stats and > @@ -6511,6 +6531,16 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) > goto enqueue_throttle; > } > > + /* > + * Re-evaluate the se hierarchy now that on_rq is true. This is > + * important to enforce uclamp the moment a task with uclamp is > + * enqueued, rather than waiting a timer tick for uclamp to kick in. > + * > + * XXX: This duplicates some of the work already done in the above for > + * loops. > + */ > + update_se_chain(p); I try to figure out why this is necessary here: enqueue_task_fair() for_each_sched_entity() enqueue_entity() update_load_avg() __update_load_avg_se() ___update_util_avg_uclamp() <-- if se->on_rq, update p (se) if we cross PELT period (1) boundaries ___decay_util_avg_uclamp_towards() <-- decay p (se) (2) enqueue_util_avg_uclamp() <-- enqueue p into cfs_rq (3) se->on_rq = 1 <-- set p (se) on_rq (4) for_each_sched_entity() update_load_avg() <-- update all on_rq se's in the hierarchy (5) update_se_chain() <-- update p (se) and its se hierarchy (6) (1) Skip p since it is !se->on_rq. (2) Decay p->se->avg.util_avg_uclamp to 0 since it was sleeping. (3) Attach p to its cfs_rq ... (6) Update all all se's and cfs_rq's involved in p's task_group hierarchy (including propagation from se (level=x+1) to cfs_rq (level=x)) Question for me is why can't you integrate the util_avg_uclamp signals for se's and cfs_rq's/rq's much closer into existing PELT functions? [...]