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_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 B91DAC432C3 for ; Fri, 15 Nov 2019 10:38:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8C61120740 for ; Fri, 15 Nov 2019 10:38:15 +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="Ynvb5DGR" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727413AbfKOKiO (ORCPT ); Fri, 15 Nov 2019 05:38:14 -0500 Received: from merlin.infradead.org ([205.233.59.134]:59142 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727365AbfKOKiN (ORCPT ); Fri, 15 Nov 2019 05:38:13 -0500 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=kF17KYqpXXxrOXvE5ZmPkjCvqdlqrYPD5aCNtqKBz40=; b=Ynvb5DGRQwGex8Q0NTJer5TLU KlzMAbWWklLqeWAgE0WFxer4N5SAkywU6V6El8MJ1ylwwM4rQKYH6wU2YzqYQ7EB941XJ7jseH62B uGh3Hl1VvE3HjmC8EWWC0y/rlsSLNjalUONSoHmPisftHOxBV0C3oScR+EhQdVX75aOwu0YN/Wuzj uOOBcWME6abYJoXrPT02rwEnOTuRzPy7DDNSSj8pU+dLCIrMkGinOVgv1JA4DSBrNMUtFBMdZB5re rT+3mIB0u/9//YqC2mNMaEgxxrMve9qZiycW0oskf54iG8Z3kcGFDFfdpHu0zrnwgp5I9yeVMxnlF 49GqRWJsg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1iVYyw-0006Pz-8Q; Fri, 15 Nov 2019 10:37:38 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 8DCD2303D9F; Fri, 15 Nov 2019 11:36:27 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 79AC42B0BC1FB; Fri, 15 Nov 2019 11:37:35 +0100 (CET) Date: Fri, 15 Nov 2019 11:37:35 +0100 From: Peter Zijlstra To: Vincent Guittot Cc: linux-kernel , Ingo Molnar , Dietmar Eggemann , Juri Lelli , Steven Rostedt , Mel Gorman , Doug Smythies , "open list:THERMAL" , Linus Torvalds , Thomas Gleixner , Sargun Dhillon , Tejun Heo , Xie XiuQi , xiezhipeng1@huawei.com, Srinivas Pandruvada Subject: Re: [PATCH v4] sched/freq: move call to cpufreq_update_util Message-ID: <20191115103735.GE4131@hirez.programming.kicks-ass.net> References: <1573751251-3505-1-git-send-email-vincent.guittot@linaro.org> <20191115095447.GU4114@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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, Nov 15, 2019 at 11:18:00AM +0100, Vincent Guittot wrote: > On Fri, 15 Nov 2019 at 10:55, Peter Zijlstra wrote: > > > > On Thu, Nov 14, 2019 at 06:07:31PM +0100, Vincent Guittot wrote: > > > update_cfs_rq_load_avg() calls cfs_rq_util_change() everytime pelt decays, > > > which might be inefficient when cpufreq driver has rate limitation. > > > > > > When a task is attached on a CPU, we have call path: > > > > > > update_load_avg() > > > update_cfs_rq_load_avg() > > > cfs_rq_util_change -- > trig frequency update > > > attach_entity_load_avg() > > > cfs_rq_util_change -- > trig frequency update > > > > > > The 1st frequency update will not take into account the utilization of the > > > newly attached task and the 2nd one might be discard because of rate > > > limitation of the cpufreq driver. > > > > Doesn't this just show that a dumb rate limit in the driver is broken? > > But the rate limit may come from HW constraints that forces to wait > let say 4ms or even 10ms between each frequency update. Sure, but then it can still remember the value passed in last and use that state later. It doesn't _have_ to completely discard values. > > > update_cfs_rq_load_avg() is only called by update_blocked_averages() > > > and update_load_avg() so we can move the call to > > > cfs_rq_util_change/cpufreq_update_util() into these 2 functions. It's also > > > interesting to notice that update_load_avg() already calls directly > > > cfs_rq_util_change() for !SMP case. > > > > > > This changes will also ensure that cpufreq_update_util() is called even > > > when there is no more CFS rq in the leaf_cfs_rq_list to update but only > > > irq, rt or dl pelt signals. > > > > I don't think it does that; that is, iirc the return value of > > ___update_load_sum() is 1 every time a period lapses. So even if the avg > > is 0 and doesn't change, it'll still return 1 on every period. > > > > Which is what that dumb rate-limit thing wants of course. But I'm still > > thinking that it's stupid to do. If nothing changes, don't generate > > events. > > When everything (irq, dl, rt, cfs) is 0, we don't generate events > because update_blocked_averages is no more called because > rq->has_blocked_load is clear Aah.. Ok, let me look at this thing again. > > If anything, update_blocked_avgerages() should look at > > @done/others_have_blocked() to emit events for rt,dl,irq. > > other_have_blocked can be set but no decay happened during the update > and we don't need to call cpufreq_update_util True.