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=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 528E5C282C3 for ; Tue, 22 Jan 2019 14:01:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2CCB921721 for ; Tue, 22 Jan 2019 14:01:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728732AbfAVOBV (ORCPT ); Tue, 22 Jan 2019 09:01:21 -0500 Received: from foss.arm.com ([217.140.101.70]:53964 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728456AbfAVOBV (ORCPT ); Tue, 22 Jan 2019 09:01:21 -0500 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 98593EBD; Tue, 22 Jan 2019 06:01:20 -0800 (PST) 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 A045B3F614; Tue, 22 Jan 2019 06:01:17 -0800 (PST) Date: Tue, 22 Jan 2019 14:01:15 +0000 From: Patrick Bellasi To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, linux-api@vger.kernel.org, Ingo Molnar , 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 , Suren Baghdasaryan Subject: Re: [PATCH v6 05/16] sched/core: uclamp: Update CPU's refcount on clamp changes Message-ID: <20190122140115.twtx646vewm757ca@e110439-lin> References: <20190115101513.2822-1-patrick.bellasi@arm.com> <20190115101513.2822-6-patrick.bellasi@arm.com> <20190121153308.GL27931@hirez.programming.kicks-ass.net> <20190121154412.fak2t2iquj3aixtu@e110439-lin> <20190122093704.GM27931@hirez.programming.kicks-ass.net> <20190122104305.6vjx37muqsxm536t@e110439-lin> <20190122132817.GG13777@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190122132817.GG13777@hirez.programming.kicks-ass.net> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 22-Jan 14:28, Peter Zijlstra wrote: > On Tue, Jan 22, 2019 at 10:43:05AM +0000, Patrick Bellasi wrote: > > On 22-Jan 10:37, Peter Zijlstra wrote: > > > > Sure, I get that. What I don't get is why you're adding that (2) here. > > > Like said, __sched_setscheduler() already does a dequeue/enqueue under > > > rq->lock, which should already take care of that. > > > > Oh, ok... got it what you mean now. > > > > With: > > > > [PATCH v6 01/16] sched/core: Allow sched_setattr() to use the current policy > > <20190115101513.2822-2-patrick.bellasi@arm.com> > > > > we can call __sched_setscheduler() with: > > > > attr->sched_flags & SCHED_FLAG_KEEP_POLICY > > > > whenever we want just to change the clamp values of a task without > > changing its class. Thus, we can end up returning from > > __sched_setscheduler() without doing an actual dequeue/enqueue. > > I don't see that happening.. when KEEP_POLICY we set attr.sched_policy = > SETPARAM_POLICY. That is then checked again in __setscheduler_param(), > which is in the middle of that dequeue/enqueue. Yes, I think I've forgot a check before we actually dequeue the task. The current code does: ---8<--- SYSCALL_DEFINE3(sched_setattr) // A) request to keep the same policy if (attr.sched_flags & SCHED_FLAG_KEEP_POLICY) attr.sched_policy = SETPARAM_POLICY; sched_setattr() // B) actually enforce the same policy if (policy < 0) policy = oldpolicy = p->policy; // C) tune the clamp values if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP) retval = __setscheduler_uclamp(p, attr); // D) tune attributes if policy is the same if (unlikely(policy == p->policy)) if (fair_policy(policy) && attr->sched_nice != task_nice(p)) goto change; if (rt_policy(policy) && attr->sched_priority != p->rt_priority) goto change; if (dl_policy(policy) && dl_param_changed(p, attr)) goto change; return 0; change: // E) dequeue/enqueue task ---8<--- So, probably in D) I've missed a check on SCHED_FLAG_KEEP_POLICY to enforce a return in that case... > Also, and this might be 'broken', SETPARAM_POLICY _does_ reset all the > other attributes, it only preserves policy, but it will (re)set nice > level for example (see that same function). Mmm... right... my bad! :/ > So maybe we want to introduce another (few?) FLAG_KEEP flag(s) that > preserve the other bits; I'm thinking at least KEEP_PARAM and KEEP_UTIL > or something. Yes, I would say we have two options: 1) SCHED_FLAG_KEEP_POLICY enforces all the scheduling class specific attributes, but cross class attributes (e.g. uclamp) 2) add SCHED_KEEP_NICE, SCHED_KEEP_PRIO, and SCED_KEEP_PARAMS and use them in the if conditions in D) In both cases the goal should be to return from code block D). What do you prefer? -- #include Patrick Bellasi