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 44ACCC2F3A6 for ; Mon, 21 Jan 2019 12:51:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 07DE62089F for ; Mon, 21 Jan 2019 12:51:40 +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="IueQTxVQ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728693AbfAUMvi (ORCPT ); Mon, 21 Jan 2019 07:51:38 -0500 Received: from merlin.infradead.org ([205.233.59.134]:49644 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728162AbfAUMvi (ORCPT ); Mon, 21 Jan 2019 07:51:38 -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=40LtdF75kj72Y8+CkoBmhdcWUTk8s4S5td/po7h0f9g=; b=IueQTxVQlRfmyC3kFHMmAS/P1 D/J+fyyk07alK8ls5REqklkc6k4ku32YspFmkqFrpjAW8GCpAzvLNsFxRxDBCsuRgAbrZDq9kp/j3 F+ojYEeEOqvG/X7It63++rAOmy68/GtJkDEqOF3h5vLJMWw8KVr8gLop8LQACd6LioC3A+X6m6M2B BVZnNNERaTcEyaWvsBfg/QpF32KWL4O7onVrO5vXNYebfCLHEKbg8H6nHrkBAGZLnQPhJDMshg0eY KEZswwO12chIuHXo7WHReGFStwI7kDSIomyMQLnYS15E8wGbY0+6LNagsMyKfeO1M+aHblope2tnS IX61Sf3Ig==; 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 1glZ2x-0003jR-SV; Mon, 21 Jan 2019 12:51:24 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 1C43A2846CE22; Mon, 21 Jan 2019 13:51:20 +0100 (CET) Date: Mon, 21 Jan 2019 13:51:20 +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 03/16] sched/core: uclamp: Map TASK's clamp values into CPU's clamp buckets Message-ID: <20190121125120.GB17749@hirez.programming.kicks-ass.net> References: <20190115101513.2822-1-patrick.bellasi@arm.com> <20190115101513.2822-4-patrick.bellasi@arm.com> <20190121101508.GH27931@hirez.programming.kicks-ass.net> <20190121122659.if6f4ubw2wgblxwi@e110439-lin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190121122659.if6f4ubw2wgblxwi@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, Jan 21, 2019 at 12:27:10PM +0000, Patrick Bellasi wrote: > On 21-Jan 11:15, Peter Zijlstra wrote: > > On Tue, Jan 15, 2019 at 10:15:00AM +0000, Patrick Bellasi wrote: > > > +/* > > > + * Number of utilization clamp buckets. > > > + * > > > + * The first clamp bucket (bucket_id=0) is used to track non clamped tasks, i.e. > > > + * util_{min,max} (0,SCHED_CAPACITY_SCALE). Thus we allocate one more bucket in > > > + * addition to the compile time configured number. > > > + */ > > > +#define UCLAMP_BUCKETS (CONFIG_UCLAMP_BUCKETS_COUNT + 1) > > > + > > > +/* > > > + * Utilization clamp bucket > > > + * @value: clamp value tracked by a clamp bucket > > > + * @bucket_id: the bucket index used by the fast-path > > > + * @mapped: the bucket index is valid > > > + * > > > + * A utilization clamp bucket maps a: > > > + * clamp value (value), i.e. > > > + * util_{min,max} value requested from userspace > > > + * to a: > > > + * clamp bucket index (bucket_id), i.e. > > > + * index of the per-cpu RUNNABLE tasks refcounting array > > > + * > > > + * The mapped bit is set whenever a task has been mapped on a clamp bucket for > > > + * the first time. When this bit is set, any: > > > + * uclamp_bucket_inc() - for a new clamp value > > > + * is matched by a: > > > + * uclamp_bucket_dec() - for the old clamp value > > > + */ > > > +struct uclamp_se { > > > + unsigned int value : bits_per(SCHED_CAPACITY_SCALE); > > > + unsigned int bucket_id : bits_per(UCLAMP_BUCKETS); > > > + unsigned int mapped : 1; > > > +}; > > > > Do we want something like: > > > > BUILD_BUG_ON(sizeof(struct uclamp_se) == sizeof(unsigned int)); > > Mmm... isn't "!=" what you mean ? Quite. > We cannot use less then an unsigned int for the fields above... am I > missing something? I wanted to ensure we don't accidentally use more. > > And/or put a limit on CONFIG_UCLAMP_BUCKETS_COUNT that guarantees that ? > > The number of buckets is currently KConfig limited to a max of 20, which gives: > > UCLAMP_BUCKETS: 21 => 5bits > > Thus, even on 32 bit targets and assuming 21bits for an "extended" > SCHED_CAPACITY_SCALE range we should always fit into an unsigned int > and have at least 6 bits for flags. > > Are you afraid of some compiler magic related to bitfields packing ? Nah, I missed the Kconfig limit and was afraid that some weird configs would end up with massively huge structures.