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 16848C43381 for ; Wed, 13 Mar 2019 13:52:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CF4CF2087C for ; Wed, 13 Mar 2019 13:52:51 +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="Cu+lrHhF" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727414AbfCMNwu (ORCPT ); Wed, 13 Mar 2019 09:52:50 -0400 Received: from merlin.infradead.org ([205.233.59.134]:49134 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726797AbfCMNwr (ORCPT ); Wed, 13 Mar 2019 09:52:47 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.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=RG53r50nPpF7IX4NqLL/cGAKut5OYQQxH5dVNDOwMc4=; b=Cu+lrHhFM4vk2Xr1IGeqsOAzB rPP/3VQ4GdWdpIWnBVOiCl88Yj7f4orNO+wgjtWDNQyN/MUOtwt79i4SRIqzy2+pYAG0SvDULbYh3 H6zv9ILFyNcY4OAO4ckEvUVxwyrDigrAQ/02NseVeMXalTo0oSHbfctRnY7SBj10B8Gm9PvVwm8WR sjcjr/XJvFE0BOIbXwBwcqDkS+XZ/oWQ05Vm8jaDZKF4pWOohpI9gekq9mzX279QZNy5EGBBf8ySx BL6hOXtWB9hEda3C/xy6PdNQhbJZa6eZtz4ar0ECSBarkVQECgpRTXKArB8guSOhuSWuBJ44EU2K2 iZFFtkKUA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1h44JD-00034s-95; Wed, 13 Mar 2019 13:52:39 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 107202028B0E8; Wed, 13 Mar 2019 14:52:38 +0100 (CET) Date: Wed, 13 Mar 2019 14:52:38 +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 v7 01/15] sched/core: uclamp: Add CPU's clamp buckets refcounting Message-ID: <20190313135238.GC5922@hirez.programming.kicks-ass.net> References: <20190208100554.32196-1-patrick.bellasi@arm.com> <20190208100554.32196-2-patrick.bellasi@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190208100554.32196-2-patrick.bellasi@arm.com> 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 Fri, Feb 08, 2019 at 10:05:40AM +0000, Patrick Bellasi wrote: > +/* > + * When a task is enqueued on a rq, the clamp bucket currently defined by the > + * task's uclamp::bucket_id is reference counted on that rq. This also > + * immediately updates the rq's clamp value if required. > + * > + * Since tasks know their specific value requested from user-space, we track > + * within each bucket the maximum value for tasks refcounted in that bucket. > + * This provide a further aggregation (local clamping) which allows to track > + * within each bucket the exact "requested" clamp value whenever all tasks > + * RUNNABLE in that bucket require the same clamp. > + */ > +static inline void uclamp_rq_inc_id(struct task_struct *p, struct rq *rq, > + unsigned int clamp_id) > +{ > + unsigned int bucket_id = p->uclamp[clamp_id].bucket_id; > + unsigned int rq_clamp, bkt_clamp, tsk_clamp; > + > + rq->uclamp[clamp_id].bucket[bucket_id].tasks++; > + > + /* > + * Local clamping: rq's buckets always track the max "requested" > + * clamp value from all RUNNABLE tasks in that bucket. > + */ > + tsk_clamp = p->uclamp[clamp_id].value; > + bkt_clamp = rq->uclamp[clamp_id].bucket[bucket_id].value; > + rq->uclamp[clamp_id].bucket[bucket_id].value = max(bkt_clamp, tsk_clamp); So, if I read this correct: - here we track a max value in a bucket, > + rq_clamp = READ_ONCE(rq->uclamp[clamp_id].value); > + WRITE_ONCE(rq->uclamp[clamp_id].value, max(rq_clamp, tsk_clamp)); > +} > + > +/* > + * When a task is dequeued from a rq, the clamp bucket reference counted by > + * the task is released. If this is the last task reference counting the rq's > + * max active clamp value, then the rq's clamp value is updated. > + * Both the tasks reference counter and the rq's cached clamp values are > + * expected to be always valid, if we detect they are not we skip the updates, > + * enforce a consistent state and warn. > + */ > +static inline void uclamp_rq_dec_id(struct task_struct *p, struct rq *rq, > + unsigned int clamp_id) > +{ > + unsigned int bucket_id = p->uclamp[clamp_id].bucket_id; > + unsigned int rq_clamp, bkt_clamp; > + > + SCHED_WARN_ON(!rq->uclamp[clamp_id].bucket[bucket_id].tasks); > + if (likely(rq->uclamp[clamp_id].bucket[bucket_id].tasks)) > + rq->uclamp[clamp_id].bucket[bucket_id].tasks--; > + > + /* > + * Keep "local clamping" simple and accept to (possibly) overboost > + * still RUNNABLE tasks in the same bucket. > + */ > + if (likely(rq->uclamp[clamp_id].bucket[bucket_id].tasks)) > + return; (Oh man, I hope that generates semi sane code; long live CSE passes I suppose) But we never decrement that bkt_clamp value on dequeue. > + bkt_clamp = rq->uclamp[clamp_id].bucket[bucket_id].value; > + > + /* The rq's clamp value is expected to always track the max */ > + rq_clamp = READ_ONCE(rq->uclamp[clamp_id].value); > + SCHED_WARN_ON(bkt_clamp > rq_clamp); > + if (bkt_clamp >= rq_clamp) { head hurts, this reads ==, how can this ever not be so? > + /* > + * Reset rq's clamp bucket value to its nominal value whenever > + * there are anymore RUNNABLE tasks refcounting it. -ENOPARSE > + */ > + rq->uclamp[clamp_id].bucket[bucket_id].value = > + uclamp_bucket_value(rq_clamp); But basically you decrement the bucket value to the nominal value. > + uclamp_rq_update(rq, clamp_id); > + } > +} Given all that, what is to stop the bucket value to climbing to uclamp_bucket_value(+1)-1 and staying there (provided there's someone runnable)? Why are we doing this... ?