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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 F3943C33CA2 for ; Thu, 9 Jan 2020 11:12:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CFA9020656 for ; Thu, 9 Jan 2020 11:12:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730535AbgAILMo (ORCPT ); Thu, 9 Jan 2020 06:12:44 -0500 Received: from foss.arm.com ([217.140.110.172]:57190 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728918AbgAILMl (ORCPT ); Thu, 9 Jan 2020 06:12:41 -0500 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 7703C31B; Thu, 9 Jan 2020 03:12:40 -0800 (PST) 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 5EEF63F703; Thu, 9 Jan 2020 03:12:38 -0800 (PST) Date: Thu, 9 Jan 2020 11:12:36 +0000 From: Qais Yousef To: Quentin Perret Cc: Ingo Molnar , Peter Zijlstra , Dietmar Eggemann , Steven Rostedt , Luis Chamberlain , Kees Cook , Iurii Zaikin , Juri Lelli , Vincent Guittot , Ben Segall , Mel Gorman , valentin.schneider@arm.com, Patrick Bellasi , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH] sched/rt: Add a new sysctl to control uclamp_util_min Message-ID: <20200109111235.auslgkuqkfsaohcd@e107158-lin.cambridge.arm.com> References: <20191220164838.31619-1-qais.yousef@arm.com> <20200107134234.GA158998@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200107134234.GA158998@google.com> User-Agent: NeoMutt/20171215 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Quentin On 01/07/20 13:42, Quentin Perret wrote: > Hi Qais, > > On Friday 20 Dec 2019 at 16:48:38 (+0000), Qais Yousef wrote: > > +/* > > + * By default RT tasks run at the maximum performance point/capacity of the > > + * system. Uclamp enforces this by always setting UCLAMP_MIN of RT tasks to > > + * SCHED_CAPACITY_SCALE. > > + * > > + * This knob allows admins to change the default behavior when uclamp is being > > + * used. In battery powered devices particularly running at the maximum > > + * capacity will increase energy consumption and shorten the battery life. > > + * > > + * This knob only affects the default value RT uses when a new RT task is > > + * forked or has just changed policy to RT and no uclamp user settings were > > + * applied (ie: the task didn't modify the default value to a new value. > > + * > > + * This knob will not override the system default values defined above. > > + */ > > I suppose this comment could go in the sysctl doc file instead ? Sure. Does it hurt to keep the comment here too though? > > > +unsigned int sysctl_sched_rt_uclamp_util_min = SCHED_CAPACITY_SCALE; > > I would suggest renaming the knob as 'sysctl_sched_rt_default_uclamp_min' > or something along those lines to make it clear it's a default value. +1 > > And for consistency with the existing code, perhaps set the default to > uclamp_none(UCLAMP_MAX) instead of an explicit SCHED_CAPACITY_SCALE? Can do. But this means you need to move the initialization to sched_init() to do a function call. Using SCHED_CAPACITY_SCALE is consistent with other uclamp sysctl definition - there's no big advantage to this code shuffling to achieve the same thing? [...] > > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c > > index e591d40fd645..19572dfc175b 100644 > > --- a/kernel/sched/rt.c > > +++ b/kernel/sched/rt.c > > @@ -2147,6 +2147,12 @@ static void pull_rt_task(struct rq *this_rq) > > */ > > static void task_woken_rt(struct rq *rq, struct task_struct *p) > > { > > + /* > > + * When sysctl_sched_rt_uclamp_util_min value is changed by the user, > > + * we apply any new value on the next wakeup, which is here. > > + */ > > + uclamp_rt_sync_default_util_min(p); > > The task has already been enqueued and sugov has been called by then I > think, so this is a bit late. You could do that in uclamp_rq_inc() maybe? Yeah that might be a better place - I'm not sure why I didn't consider it. I'll try it out. > > > + > > if (!task_running(rq, p) && > > !test_tsk_need_resched(rq->curr) && > > p->nr_cpus_allowed > 1 && > > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > > index 280a3c735935..337bf17b1a9d 100644 > > --- a/kernel/sched/sched.h > > +++ b/kernel/sched/sched.h > > @@ -2300,6 +2300,8 @@ static inline void cpufreq_update_util(struct rq *rq, unsigned int flags) {} > > #endif /* CONFIG_CPU_FREQ */ > > > > #ifdef CONFIG_UCLAMP_TASK > > +void uclamp_rt_sync_default_util_min(struct task_struct *p); > > + > > unsigned int uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id); > > > > static __always_inline > > @@ -2330,6 +2332,8 @@ static inline unsigned int uclamp_util(struct rq *rq, unsigned int util) > > return uclamp_util_with(rq, util, NULL); > > } > > #else /* CONFIG_UCLAMP_TASK */ > > +void uclamp_rt_sync_default_util_min(struct task_struct *p) {} > > + > > static inline unsigned int uclamp_util_with(struct rq *rq, unsigned int util, > > struct task_struct *p) > > { > > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > > index 70665934d53e..06183762daac 100644 > > --- a/kernel/sysctl.c > > +++ b/kernel/sysctl.c > > @@ -465,6 +465,13 @@ static struct ctl_table kern_table[] = { > > .mode = 0644, > > .proc_handler = sysctl_sched_uclamp_handler, > > }, > > + { > > + .procname = "sched_rt_util_clamp_min", > > + .data = &sysctl_sched_rt_uclamp_util_min, > > + .maxlen = sizeof(unsigned int), > > + .mode = 0644, > > + .proc_handler = sysctl_sched_uclamp_handler, > > + }, > > #endif > > #ifdef CONFIG_SCHED_AUTOGROUP > > { > > -- > > 2.17.1 > > > > Apart from the small things above, this seems like a sensible idea and > would indeed be useful, so thanks for the patch! Thanks for having a look! -- Qais Yousef