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 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 72CBAC4321D for ; Thu, 16 Aug 2018 17:11:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 28C7020C07 for ; Thu, 16 Aug 2018 17:11:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 28C7020C07 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.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 S1729189AbeHPUKz (ORCPT ); Thu, 16 Aug 2018 16:10:55 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:39136 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728993AbeHPUKy (ORCPT ); Thu, 16 Aug 2018 16:10:54 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 7CC1D7A9; Thu, 16 Aug 2018 10:11:10 -0700 (PDT) Received: from [0.0.0.0] (e107985-lin.emea.arm.com [10.4.12.239]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 506BF3F5B3; Thu, 16 Aug 2018 10:11:01 -0700 (PDT) Subject: Re: [PATCH v3 07/14] sched/core: uclamp: enforce last task UCLAMP_MAX To: Patrick Bellasi Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Ingo Molnar , Peter Zijlstra , Tejun Heo , "Rafael J . Wysocki" , Viresh Kumar , Vincent Guittot , Paul Turner , Morten Rasmussen , Juri Lelli , Todd Kjos , Joel Fernandes , Steve Muckle , Suren Baghdasaryan References: <20180806163946.28380-1-patrick.bellasi@arm.com> <20180806163946.28380-8-patrick.bellasi@arm.com> <2366fe11-db1f-4f39-df03-960535611319@arm.com> <20180816164745.GF2960@e110439-lin> From: Dietmar Eggemann Message-ID: Date: Thu, 16 Aug 2018 19:10:58 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20180816164745.GF2960@e110439-lin> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/16/2018 06:47 PM, Patrick Bellasi wrote: > On 16-Aug 17:43, Dietmar Eggemann wrote: >> On 08/06/2018 06:39 PM, Patrick Bellasi wrote: >>> When a util_max clamped task sleeps, its clamp constraints are removed >> >from the CPU. However, the blocked utilization on that CPU can still be >>> higher than the max clamp value enforced while that task was running. >>> This max clamp removal when a CPU is going to be idle could thus allow >>> unwanted CPU frequency increases, right while the task is not running. >> >> So 'rq->uclamp.flags == UCLAMP_FLAG_IDLE' means CPU is IDLE because >> non-clamped tasks are tracked as well ((group_id = 0)). > > Right, but... with (group_id = 0) you mean that "non-clamped tasks are > tracked" in the first clamp group? Yes. I was asking myself what will happen if there are only non-clamped tasks runnable ... > >> Maybe this is worth mentioning here? > > Maybe I can explicitely say that we detect that there are not RUNNABLE > tasks because all the clamp groups are in UCLAMP_NOT_VALID status. Yes, would have helped me the grasp this earlier ... [...] >>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >>> index bc2beedec7bf..ff76b000bbe8 100644 >>> --- a/kernel/sched/core.c >>> +++ b/kernel/sched/core.c >>> @@ -906,7 +906,8 @@ uclamp_group_find(int clamp_id, unsigned int clamp_value) >>> * For the specified clamp index, this method computes the new CPU utilization >>> * clamp to use until the next change on the set of RUNNABLE tasks on that CPU. >>> */ >>> -static inline void uclamp_cpu_update(struct rq *rq, int clamp_id) >>> +static inline void uclamp_cpu_update(struct rq *rq, int clamp_id, >>> + unsigned int last_clamp_value) >>> { >>> struct uclamp_group *uc_grp = &rq->uclamp.group[clamp_id][0]; >>> int max_value = UCLAMP_NOT_VALID; >>> @@ -924,6 +925,19 @@ static inline void uclamp_cpu_update(struct rq *rq, int clamp_id) >> >> The condition: >> >> if (!uclamp_group_active(uc_grp, group_id)) >> continue; >> >> in 'for (group_id = 0; group_id <= CONFIG_UCLAMP_GROUPS_COUNT; ++group_id) >> {}' makes sure that 'max_value == UCLAMP_NOT_VALID' is true for the if >> condition (*): >> >> >>> if (max_value >= SCHED_CAPACITY_SCALE) >>> break; >>> } >>> + >>> + /* >>> + * Just for the UCLAMP_MAX value, in case there are no RUNNABLE >>> + * task, we keep the CPU clamped to the last task's clamp value. >>> + * This avoids frequency spikes to MAX when one CPU, with an high >>> + * blocked utilization, sleeps and another CPU, in the same frequency >>> + * domain, do not see anymore the clamp on the first CPU. >>> + */ >>> + if (clamp_id == UCLAMP_MAX && max_value == UCLAMP_NOT_VALID) { >>> + rq->uclamp.flags |= UCLAMP_FLAG_IDLE; >>> + max_value = last_clamp_value; >>> + } >>> + >> >> (*): So the uc_grp[group_id].value stays last_clamp_value? > > A bit confusing... but I think you've got the point. OK. > >> What do you do when the blocked utilization decays below this enforced >> last_clamp_value on that CPU? > > This is done _just_ for max_util: > - it clamps a blocked utilization bigger then last_clamp_value > thus avoiding the selection of an OPP bigger then the one enforced > while the task was runnable > - it has not effect on a blocked utilization smaller then last_clamp_value > thus allowing to reduce gracefully the OPP as long as the blocked > utilization is decayed Ah correct, max_util is about capping, not boosting. > >> I assume there are plenty of this kind of corner cases because we have >> blocked signals (including all tasks) and clamping (including runnable >> tasks). > > This is a pretty compelling one I've noticed in my tests and thus > worth a fix... I don't have on hand other similar corner cases, do > you? No not right now, will continue to watch out for them ...