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 6053DC282C3 for ; Thu, 24 Jan 2019 15:12:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2D064218AE for ; Thu, 24 Jan 2019 15:12:39 +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="uc1/uLVX" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728386AbfAXPMg (ORCPT ); Thu, 24 Jan 2019 10:12:36 -0500 Received: from merlin.infradead.org ([205.233.59.134]:55800 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727996AbfAXPMf (ORCPT ); Thu, 24 Jan 2019 10:12:35 -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=p3DLEMwl1y2+AhetxSrpIUDwy+GX3h7Gw1uvn5TEME0=; b=uc1/uLVXqhz4xsQJHbnjlKkRS 4/2VIRZ4DC8I3jAt5ARNIxiRJTv/n0aySuDt4Cs5j1ij0ZPI2nQAYKNVGg5R9+z/vSLkhvFrWlDrN ZY9ODMax+QPxudQsBLZvR5oO7IyWNOwX3mENFl3T7l/lAfPj2GJfce46Og4bo5Z/F+EZ2x2FxLUwg oq1psaP8meBkQDQRNOLvH4v2o5FaDTWX5pC+GQev2bfyW82YkLtq3xeIdjCo2GVK+vDNE/1T/RwS2 tdAa3fld7Ytq0e2QaQ+PKmLeINmtCFUFfLt5ICKSCZ4rmmSmbhqPLMm4AOPNS0o3PoLGusdvcUW8q b63KfoH4g==; 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 1gmgfu-00046Z-K2; Thu, 24 Jan 2019 15:12:14 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 22198238BB05C; Thu, 24 Jan 2019 16:12:12 +0100 (CET) Date: Thu, 24 Jan 2019 16:12:12 +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 09/16] sched/cpufreq: uclamp: Add utilization clamping for RT tasks Message-ID: <20190124151212.GO13777@hirez.programming.kicks-ass.net> References: <20190115101513.2822-1-patrick.bellasi@arm.com> <20190115101513.2822-10-patrick.bellasi@arm.com> <20190123104944.GX27931@hirez.programming.kicks-ass.net> <20190123144011.iid3avb63r5v4r2c@e110439-lin> <20190123201146.GH17749@hirez.programming.kicks-ass.net> <20190124123009.2yulcf25ld66popd@e110439-lin> <20190124123835.nliwk2onvrhe5aqf@e110439-lin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190124123835.nliwk2onvrhe5aqf@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 Thu, Jan 24, 2019 at 12:38:35PM +0000, Patrick Bellasi wrote: > On 24-Jan 12:30, Patrick Bellasi wrote: > > On 23-Jan 21:11, Peter Zijlstra wrote: > > > On Wed, Jan 23, 2019 at 02:40:11PM +0000, Patrick Bellasi wrote: > > > > On 23-Jan 11:49, Peter Zijlstra wrote: > > > > > On Tue, Jan 15, 2019 at 10:15:06AM +0000, Patrick Bellasi wrote: > > [...] > > > > I'm thikning that if we haz a single bit, say: > > > > > > struct uclamp_se { > > > ... > > > unsigned int changed : 1; > > > }; > > > > > > We can update uclamp_se::value and set uclamp_se::changed, and then the > > > next enqueue will (unlikely) test-and-clear changed and recompute the > > > bucket_id. > > > > This mean will lazy update the "requested" bucket_id by deferring its > > computation at enqueue time. Which saves us a copy of the bucket_id, > > i.e. we will have only the "effective" value updated at enqueue time. > > > > But... > > > > > Would that not be simpler? > > > > ... although being simpler it does not fully exploit the slow-path, > > a syscall which is usually running from a different process context > > (system management software). > > > > It also fits better for lazy updates but, in the cgroup case, where we > > wanna enforce an update ASAP for RUNNABLE tasks, we will still have to > > do the updates from the slow-path. > > > > Will look better into this simplification while working on v7, perhaps > > the linear mapping can really help in that too. > > Actually, I forgot to mention that: > > uclamp_se::effective::{ > value, bucket_id > } > > will be still required to proper support the cgroup delegation model, > where a child group could be restricted by the parent but we want to > keep track of the original "requested" value for when the parent > should relax the restriction. > > Thus, since effective values are already there, why not using them > also to pre-compute the new requested bucket_id from the slow path? Well, we need the orig_value; but I'm still not sure why you need more bucket_id's. Also, retaining orig_value is already required for the system limits, there's nothing cgroup-y about this afaict.