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=-2.1 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, 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 A7253ECE560 for ; Mon, 24 Sep 2018 16:27:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 379202087A for ; Mon, 24 Sep 2018 16:27:05 +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="cW8pkVWn" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 379202087A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731142AbeIXW37 (ORCPT ); Mon, 24 Sep 2018 18:29:59 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:59692 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730507AbeIXW36 (ORCPT ); Mon, 24 Sep 2018 18:29:58 -0400 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=dqqSZ8YvAX0EwDqB0f6MQiQThrNZOmSXNQ77OylbiAY=; b=cW8pkVWnQTWSA72ZoepcjgLcf OA1eZfEs/N3mU6yBB9bI0KaTSM/2DH2sgg1CdRNKH+QKKV0baO1bmZGy1BX8HCdAZEdcbpQArIOzX TZwir4MO3KhseQepTRpar2ec41WrStWlErYo5uVN9XAnriQcunYW6K6uov+IZlvk/TAS4JNnh4tgu aFxDsGY617BlWgph0QZYiGkbF4Uz9LGUqQEX/ST3xRR+0sTyDy1MDGJmwegEXWIb9OBrkSPZ0a1ly BRj5A0A9/qLkjbx9nzkA9Rl6oq4dBgm//xUjGPfLwfxQ5W/n8/8kQKBUd4IAX8V3EW8TQcz6TUqCE Z8aI8mFgQ==; 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 1g4Th5-0007Xk-M0; Mon, 24 Sep 2018 16:26:57 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id A89EB20289D0D; Mon, 24 Sep 2018 18:26:40 +0200 (CEST) Date: Mon, 24 Sep 2018 18:26:40 +0200 From: Peter Zijlstra To: Patrick Bellasi Cc: Juri Lelli , linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Ingo Molnar , Tejun Heo , "Rafael J . Wysocki" , Viresh Kumar , Vincent Guittot , Paul Turner , Quentin Perret , Dietmar Eggemann , Morten Rasmussen , Todd Kjos , Joel Fernandes , Steve Muckle , Suren Baghdasaryan Subject: Re: [PATCH v4 14/16] sched/core: uclamp: request CAP_SYS_ADMIN by default Message-ID: <20180924162640.GB7060@hirez.programming.kicks-ass.net> References: <20180828135324.21976-1-patrick.bellasi@arm.com> <20180828135324.21976-15-patrick.bellasi@arm.com> <20180904134748.GA4974@localhost.localdomain> <20180906144053.GD25636@e110439-lin> <20180914111003.GC24082@hirez.programming.kicks-ass.net> <20180914140732.GR1413@e110439-lin> <20180914142813.GM24124@hirez.programming.kicks-ass.net> <20180917122723.GS1413@e110439-lin> <20180921091308.GD24082@hirez.programming.kicks-ass.net> <20180924151400.GT1413@e110439-lin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180924151400.GT1413@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, Sep 24, 2018 at 04:14:00PM +0100, Patrick Bellasi wrote: > ... still it's difficult to give a precise definition of knee point, > unless you know about platforms which have a sharp change in energy > efficiency. > > The only cases we know about are those where: > > A) multiple frequencies uses the same voltage, e.g. > > > ^ * > | Energy O > | efficiency O+ > | O | > | O* | > | O** | > | O** O*** | > | + O** O**** | > | | O** O***** | > | | O** | > | | + | > | | Same V | Increasing V | > +---+----------+----------------------+-----------> > | | | Frequency > L M H > > B) there is a big frequency gap between low frequency OPPs and high > frequency OPPs, e.g. > > O > ^ **+ > | Energy ** | > | efficiency ** | > | ** | > | ** | > | ** | > | ** | > | ** | > | O** | > | O******+ | > |O******* | | > | | | > ++--------------+------------------+------> > | | | Frequency > L M H > > > In case A, all the OPPs left of M are dominated by M in terms > of energy efficiency and normally they should be never used. > Unless you are under thermal constraints and you still want to keep > your code running even if at a lower rate and energy efficiency. > At this point, however, you already invalidated all the OPPs right of > M and, on the remaining, you still struggle do define the knee point. > > In case B... I'm wondering it such a conf even makes sense ;) > Is there really some platform out there with such a "non homogeneously > distributed" set of available frequencies ? Well, the curve is a second or third order polynomial (when V~f -> fV^2 -> f^3), so it shoots up at some point. There's not really anything you can do about that. But if you're willing to put in active cooling and lots of energy, you can make it go fast :-) Therefore I was thinking: > Maybe we can define a threshold > for a "EE derivative ratio", but it will still be quite arbitrary. Because up until de/df=.5 we gain more performance than we loose ee. But I might not have appreciated the fact that when we work with imaginary cost units that skews the .5.