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=-8.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_NEOMUTT 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 E71BFC004C9 for ; Tue, 7 May 2019 11:25:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C329E2054F for ; Tue, 7 May 2019 11:25:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726526AbfEGLZ3 (ORCPT ); Tue, 7 May 2019 07:25:29 -0400 Received: from foss.arm.com ([217.140.101.70]:51482 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725843AbfEGLZ2 (ORCPT ); Tue, 7 May 2019 07:25:28 -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 CAE0B374; Tue, 7 May 2019 04:25:27 -0700 (PDT) Received: from e110439-lin (e110439-lin.cambridge.arm.com [10.1.194.43]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CCE833F5AF; Tue, 7 May 2019 04:25:24 -0700 (PDT) Date: Tue, 7 May 2019 12:25:22 +0100 From: Patrick Bellasi To: Suren Baghdasaryan Cc: LKML , linux-pm@vger.kernel.org, linux-api@vger.kernel.org, Ingo Molnar , Peter Zijlstra , Tejun Heo , "Rafael J . Wysocki" , Vincent Guittot , Viresh Kumar , Paul Turner , Quentin Perret , Dietmar Eggemann , Morten Rasmussen , Juri Lelli , Todd Kjos , Joel Fernandes , Steve Muckle Subject: Re: [PATCH v8 08/16] sched/core: uclamp: Set default clamps for RT tasks Message-ID: <20190507112522.g2gaydwfkczb33je@e110439-lin> References: <20190402104153.25404-1-patrick.bellasi@arm.com> <20190402104153.25404-9-patrick.bellasi@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17-Apr 16:07, Suren Baghdasaryan wrote: > On Tue, Apr 2, 2019 at 3:42 AM Patrick Bellasi wrote: > > > > By default FAIR tasks start without clamps, i.e. neither boosted nor > > capped, and they run at the best frequency matching their utilization > > demand. This default behavior does not fit RT tasks which instead are > > expected to run at the maximum available frequency, if not otherwise > > required by explicitly capping them. > > > > Enforce the correct behavior for RT tasks by setting util_min to max > > whenever: > > > > 1. the task is switched to the RT class and it does not already have a > > user-defined clamp value assigned. > > > > 2. an RT task is forked from a parent with RESET_ON_FORK set. > > > > NOTE: utilization clamp values are cross scheduling class attributes and > > thus they are never changed/reset once a value has been explicitly > > defined from user-space. > > > > Signed-off-by: Patrick Bellasi > > Cc: Ingo Molnar > > Cc: Peter Zijlstra > > --- > > kernel/sched/core.c | 26 ++++++++++++++++++++++++++ > > 1 file changed, 26 insertions(+) > > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > index bdebdabe9bc4..71c9dd6487b1 100644 > > --- a/kernel/sched/core.c > > +++ b/kernel/sched/core.c > > @@ -1042,6 +1042,28 @@ static int uclamp_validate(struct task_struct *p, > > static void __setscheduler_uclamp(struct task_struct *p, > > const struct sched_attr *attr) > > { > > + unsigned int clamp_id; > > + > > + /* > > + * On scheduling class change, reset to default clamps for tasks > > + * without a task-specific value. > > + */ > > + for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id) { > > + struct uclamp_se *uc_se = &p->uclamp_req[clamp_id]; > > + unsigned int clamp_value = uclamp_none(clamp_id); > > + > > + /* Keep using defined clamps across class changes */ > > + if (uc_se->user_defined) > > + continue; > > + > > + /* By default, RT tasks always get 100% boost */ > > + if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN)) > > + clamp_value = uclamp_none(UCLAMP_MAX); > > + > > + uc_se->bucket_id = uclamp_bucket_id(clamp_value); > > + uc_se->value = clamp_value; > > Is it possible for p->uclamp_req[UCLAMP_MAX].value to be less than > uclamp_none(UCLAMP_MAX) for this RT task? If that's a possibility then > I think we will end up with a case of > p->uclamp_req[UCLAMP_MIN].value > p->uclamp_req[UCLAMP_MAX].value > after these assignments are done. > The util_max for an RT task can be less then uclamp_none(UCLAMP_MAX), however, requesting a task specific util_max which is smaller then the current util_min will fail in: __sched_setscheduler() uclamp_validate() since we only allow util_min <= util_max for all task specific values. > > + } > > + > > if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP))) > > return; > > > > @@ -1077,6 +1099,10 @@ static void uclamp_fork(struct task_struct *p) > > for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id) { > > unsigned int clamp_value = uclamp_none(clamp_id); > > > > + /* By default, RT tasks always get 100% boost */ > > + if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN)) > > + clamp_value = uclamp_none(UCLAMP_MAX); > > + > > p->uclamp_req[clamp_id].user_defined = false; > > p->uclamp_req[clamp_id].value = clamp_value; > > p->uclamp_req[clamp_id].bucket_id = uclamp_bucket_id(clamp_value); > > -- > > 2.20.1 > > -- #include Patrick Bellasi