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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 2D5DFECE58E for ; Thu, 17 Oct 2019 19:07:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EE0E421848 for ; Thu, 17 Oct 2019 19:07:28 +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="qDpcNx0M" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2503364AbfJQTH2 (ORCPT ); Thu, 17 Oct 2019 15:07:28 -0400 Received: from merlin.infradead.org ([205.233.59.134]:56398 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2503363AbfJQTH2 (ORCPT ); Thu, 17 Oct 2019 15:07:28 -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=+iW1UtqQMUkClFUP9OfZlGcJ+KCRuTpNF/TmgYgEt/U=; b=qDpcNx0MrDAxV3GnJa1A1QBrl LL68RwtKOpen/rD5D+jpGbpw5+hc1x2D026QEBabOT0ees4y12rAy5nSS4GP3BnW8tpN4LUj18pnJ IVqQ37CIMfGDNo2TZhFN2UWA/07SrsI7pR4lOoChHRVT5XOYFuZKPhD9JldIfu02/DxU2UsbZnksd VKIbAJfH1RbOzLJ1ei+g2SazqlbY1h0nndbWi5c2cUV0cIB54q7U8sCmlarmns6F8gZUuPv3nFfxS IV/l4I53sLlRnjnrtLG8p+RsPJLa2P90vxBWcIdkoQ/nt4ZWc2kF5HI5e9BMtoCSw9mRHqPucTXen NtMDFjJIg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=worktop.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1iLB7A-0005Tu-9Y; Thu, 17 Oct 2019 19:07:12 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id BCD86980D8F; Thu, 17 Oct 2019 21:07:08 +0200 (CEST) Date: Thu, 17 Oct 2019 21:07:08 +0200 From: Peter Zijlstra To: Douglas Raillard Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, mingo@redhat.com, rjw@rjwysocki.net, viresh.kumar@linaro.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, qperret@qperret.net, patrick.bellasi@matbug.net, dh.han@samsung.com Subject: Re: [RFC PATCH v3 0/6] sched/cpufreq: Make schedutil energy aware Message-ID: <20191017190708.GF22902@worktop.programming.kicks-ass.net> References: <20191011134500.235736-1-douglas.raillard@arm.com> <20191014145315.GZ2311@hirez.programming.kicks-ass.net> <20191017095015.GI2311@hirez.programming.kicks-ass.net> <7edb1b73-54e7-5729-db5d-6b3b1b616064@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7edb1b73-54e7-5729-db5d-6b3b1b616064@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org On Thu, Oct 17, 2019 at 03:23:04PM +0100, Douglas Raillard wrote: > On 10/17/19 10:50 AM, Peter Zijlstra wrote: > > I'm still thinking about the exact means you're using to raise C; that > > is, the 'util - util_est' as cost_margin. It hurts my brain still. > > util_est is currently the best approximation of the actual portion of the CPU the task needs: > 1) for periodic tasks, it's not too far from the duty cycle, and is always higher > > 2) for aperiodic tasks, it (indirectly) takes into account the total time it took > to complete the previous activation, so the signal is not 100% composed of logical signals > only relevant for periodic tasks (although it's a big part of it). > > 3) Point 1) and 2) together allows util_est to adapt to periodic tasks that changes > their duty cycle over time, without needing a very long history (the last task period > is sufficient). > > For periodic tasks, the distance between instantaneous util_avg and the actual task > duty cycle indicates somehow what is our best guess of the (potential) change in the task > duty cycle. > > util_est is the threshold (assuming util_avg increasing) for util_avg after which we know > for sure that even if the task stopped right now, its duty cycle would be higher than > during the previous period. > This means for a given task and with (util >= util_est): > > 1) util - util_est == 0 means the task duty cycle will be equal to the one during > during the previous activation, if the tasks stopped executing right now. > > 2) util - util_est > 0 means the task duty cycle will be higher to the one during > during the previous activation, if the tasks stopped executing right now. So far I can follow, 2) is indeed a fairly sane indication that utilization is growing. > Using the difference (util - util_est) will therefore give these properties to the boost signal: > * no boost will be applied as long as the task has a constant or decreasing duty cycle. > > * when we can detect that the duty cycle increases, we temporarily increase the frequency. > We start with a slight increase, and the longer we wait for the current period to finish, > the more we boost, since the more likely it is that the task has a much larger duty cycle > than anticipated. More specifically, the evaluation of "how much more" is done the exact > same way as it is done for PELT, since the dynamic of the boost is "inherited" from PELT. Right, because as long it keeps running, util_est will not be changed, so the difference will continue to increase. What I don't see is how that that difference makes sense as input to: cost(x) : (1 + x) * cost_j I suppose that limits the additional OPP to twice the previously selected cost / efficiency (see the confusion from that other email). But given that efficency drops (or costs rise) for higher OPPs that still doesn't really make sense.. > Now if the task is aperiodic, the boost will allow reaching the highest frequency faster, > which may or may not be desired. Ultimately, it's not more or less wrong than just picking > the freq based on util_est alone, since util_est is already somewhat meaningless for aperiodic > tasks. It just allows reaching the max freq at some point without waiting for too long, which is > all what we can do without more info on the task. > > When applying these boosting rules on the runqueue util signals, we are able to detect if at least one > task needs boosting according to these rules. That only holds as long as the history we look at is > the result of a stable set of tasks, i.e. no tasks added or removed from the rq. So while I agree that 2) is a reasonable signal to work from, everything that comes after is still much confusing me.