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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 CCF05C433DF for ; Wed, 24 Jun 2020 10:36:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AB3B12088E for ; Wed, 24 Jun 2020 10:36:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390483AbgFXKgY (ORCPT ); Wed, 24 Jun 2020 06:36:24 -0400 Received: from foss.arm.com ([217.140.110.172]:59922 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390441AbgFXKgY (ORCPT ); Wed, 24 Jun 2020 06:36:24 -0400 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 11BEE1FB; Wed, 24 Jun 2020 03:36:23 -0700 (PDT) Received: from e107158-lin.cambridge.arm.com (e107158-lin.cambridge.arm.com [10.1.195.21]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8129F3F6CF; Wed, 24 Jun 2020 03:36:21 -0700 (PDT) Date: Wed, 24 Jun 2020 11:36:19 +0100 From: Qais Yousef To: Patrick Bellasi Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Chris Redpath , Lukasz Luba , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/2] sched/uclamp: Fix initialization of strut uclamp_rq Message-ID: <20200624103618.zkk2unblc265v4mo@e107158-lin.cambridge.arm.com> References: <20200619172011.5810-1-qais.yousef@arm.com> <20200619172011.5810-2-qais.yousef@arm.com> <87sgekorfq.derkling@matbug.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <87sgekorfq.derkling@matbug.net> User-Agent: NeoMutt/20171215 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/24/20 09:26, Patrick Bellasi wrote: > > Hi Qais, > > On Fri, Jun 19, 2020 at 19:20:10 +0200, Qais Yousef wrote... > > > struct uclamp_rq was zeroed out entirely in assumption that in the first > > call to uclamp_rq_inc() they'd be initialized correctly in accordance to > > default settings. > > > > But when next patch introduces a static key to skip > > uclamp_rq_{inc,dec}() until userspace opts in to use uclamp, schedutil > > will fail to perform any frequency changes because the > > rq->uclamp[UCLAMP_MAX].value is zeroed at init and stays as such. Which > > means all rqs are capped to 0 by default. > > Does not this means the problem is more likely with uclamp_rq_util_with(), > which should be guarded? The initialization is wrong and needs to be fixed, no? So I won't say uclamp_rq_util_with() has any problem. For RT boosting to work as-is, uclamp_rq_util_with() needs to stay the same, otherwise we need to add extra logic to deal with that. Which I don't think is worth it or necessary. The function is called from sugov and find_energy_efficient_cpu(), both of which aren't a worry to make this call unconditionally IMO. Thanks -- Qais Yousef > > Otherwise, we will also keep doing useless min/max aggregations each > time schedutil calls that function, thus not completely removing > uclamp overheads while user-space has not opted in. > > What about dropping this and add the guard in the following patch, along > with the others? > > > Fix it by making sure we do proper initialization at init without > > > > > Fix it by making sure we do proper initialization at init without > > relying on uclamp_rq_inc() doing it later. > > > > Fixes: 69842cba9ace ("sched/uclamp: Add CPU's clamp buckets refcounting") > > Signed-off-by: Qais Yousef > > Cc: Juri Lelli > > Cc: Vincent Guittot > > Cc: Dietmar Eggemann > > Cc: Steven Rostedt > > Cc: Ben Segall > > Cc: Mel Gorman > > CC: Patrick Bellasi > > Cc: Chris Redpath > > Cc: Lukasz Luba > > Cc: linux-kernel@vger.kernel.org > > --- > > kernel/sched/core.c | 23 ++++++++++++++++++----- > > 1 file changed, 18 insertions(+), 5 deletions(-) > > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > index a43c84c27c6f..4265861e13e9 100644 > > --- a/kernel/sched/core.c > > +++ b/kernel/sched/core.c > > @@ -1248,6 +1248,22 @@ static void uclamp_fork(struct task_struct *p) > > } > > } > > > > +static void __init init_uclamp_rq(struct rq *rq) > > +{ > > + enum uclamp_id clamp_id; > > + struct uclamp_rq *uc_rq = rq->uclamp; > > + > > + for_each_clamp_id(clamp_id) { > > + memset(uc_rq[clamp_id].bucket, > > + 0, > > + sizeof(struct uclamp_bucket)*UCLAMP_BUCKETS); > > + > > + uc_rq[clamp_id].value = uclamp_none(clamp_id); > > + } > > + > > + rq->uclamp_flags = 0; > > +} > > + > > static void __init init_uclamp(void) > > { > > struct uclamp_se uc_max = {}; > > @@ -1256,11 +1272,8 @@ static void __init init_uclamp(void) > > > > mutex_init(&uclamp_mutex); > > > > - for_each_possible_cpu(cpu) { > > - memset(&cpu_rq(cpu)->uclamp, 0, > > - sizeof(struct uclamp_rq)*UCLAMP_CNT); > > - cpu_rq(cpu)->uclamp_flags = 0; > > - } > > + for_each_possible_cpu(cpu) > > + init_uclamp_rq(cpu_rq(cpu)); > > > > for_each_clamp_id(clamp_id) { > > uclamp_se_set(&init_task.uclamp_req[clamp_id], >