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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 04B06C282C3 for ; Tue, 22 Jan 2019 09:37:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C45C9218D0 for ; Tue, 22 Jan 2019 09:37:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="PW0gNWBL" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727929AbfAVJhM (ORCPT ); Tue, 22 Jan 2019 04:37:12 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:47758 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727026AbfAVJhL (ORCPT ); Tue, 22 Jan 2019 04:37:11 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=NU4V5uCQmV84QkTw0S+I2r8MuzPTPNrPYuSs+2uS5y4=; b=PW0gNWBLoYOCSz6mnwSOOsGrA Dxn2PRND+3H1sRQoZWifWHelGjQUeRKM/R8+nBIpI3flVLfRp9ZPQvC9emuHNTXk3hXHON6X4PKI2 qxk8UpjShmuoenwoZqSR4KmsetHZlfc+GS1BefEqhA2vxUCKMFbC6t5zBlS4t1zd0iMxQv3Ckk/ub lRfYeTKuZoqUErQEpzC0UAiMPlv52D8Po64jx7lw2tBqEVupQBrrwnwksfqG8mh+9mFLSNmBtlSvD /xz4BaeLTVf5pdqwBf0Sxx+uwypVB+o0tZDqd8XFvh8knuUAgnK0cpDpRHrkF8zbkVhuo+mTaYjoD mGYGy8N0g==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1glsUU-0001FV-MW; Tue, 22 Jan 2019 09:37:06 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 9B6BD211A59B4; Tue, 22 Jan 2019 10:37:04 +0100 (CET) Date: Tue, 22 Jan 2019 10:37:04 +0100 From: Peter Zijlstra To: Patrick Bellasi 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: <20190122093704.GM27931@hirez.programming.kicks-ass.net> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190121154412.fak2t2iquj3aixtu@e110439-lin> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 21, 2019 at 03:44:12PM +0000, Patrick Bellasi wrote: > On 21-Jan 16:33, Peter Zijlstra wrote: > > On Tue, Jan 15, 2019 at 10:15:02AM +0000, Patrick Bellasi wrote: > > > > > +static inline void > > > +uclamp_task_update_active(struct task_struct *p, unsigned int clamp_id) > > > +{ > > > + struct rq_flags rf; > > > + struct rq *rq; > > > + > > > + /* > > > + * Lock the task and the CPU where the task is (or was) queued. > > > + * > > > + * We might lock the (previous) rq of a !RUNNABLE task, but that's the > > > + * price to pay to safely serialize util_{min,max} updates with > > > + * enqueues, dequeues and migration operations. > > > + * This is the same locking schema used by __set_cpus_allowed_ptr(). > > > + */ > > > + rq = task_rq_lock(p, &rf); > > > + > > > + /* > > > + * Setting the clamp bucket is serialized by task_rq_lock(). > > > + * If the task is not yet RUNNABLE and its task_struct is not > > > + * affecting a valid clamp bucket, the next time it's enqueued, > > > + * it will already see the updated clamp bucket value. > > > + */ > > > + if (!p->uclamp[clamp_id].active) > > > + goto done; > > > + > > > + uclamp_cpu_dec_id(p, rq, clamp_id); > > > + uclamp_cpu_inc_id(p, rq, clamp_id); > > > + > > > +done: > > > + task_rq_unlock(rq, p, &rf); > > > +} > > > > > @@ -1008,11 +1043,11 @@ static int __setscheduler_uclamp(struct task_struct *p, > > > > > > mutex_lock(&uclamp_mutex); > > > if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) { > > > - uclamp_bucket_inc(&p->uclamp[UCLAMP_MIN], > > > + uclamp_bucket_inc(p, &p->uclamp[UCLAMP_MIN], > > > UCLAMP_MIN, lower_bound); > > > } > > > if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX) { > > > - uclamp_bucket_inc(&p->uclamp[UCLAMP_MAX], > > > + uclamp_bucket_inc(p, &p->uclamp[UCLAMP_MAX], > > > UCLAMP_MAX, upper_bound); > > > } > > > mutex_unlock(&uclamp_mutex); > > > > > > But.... __sched_setscheduler() actually does the whole dequeue + enqueue > > thing already ?!? See where it does __setscheduler(). > > This is slow-path accounting, not fast path. Sure; but that's still no reason for duplicate or unneeded code. > There are two refcounting going on here: > > 1) mapped buckets: > > clamp_value <--(M1)--> bucket_id > > 2) RUNNABLE tasks: > > bucket_id <--(M2)--> RUNNABLE tasks in a bucket > > What we fix here is the refcounting for the buckets mapping. If a task > does not have a task specific clamp value it does not refcount any > bucket. The moment we assign a task specific clamp value, we need to > refcount the task in the bucket corresponding to that clamp value. > > This will keep the bucket in use at least as long as the task will > need that clamp value. 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.