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 AAD45C3A59B for ; Mon, 2 Sep 2019 07:47:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7F78F2173E for ; Mon, 2 Sep 2019 07:47:33 +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="ekpdxU+k" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729857AbfIBHrd (ORCPT ); Mon, 2 Sep 2019 03:47:33 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:46724 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729382AbfIBHrc (ORCPT ); Mon, 2 Sep 2019 03:47:32 -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=fYldPtPtIGj2tv2z5tJVF8kAtfN8pBR+/NHizVHdMpM=; b=ekpdxU+knZnMh5434px+hOBhu xgI39mMze/viBKrF5jrQZH+mkLMoohlXfDe0/u13CYG3hXiDHMPeOz4UjmmXWLN5Ti389lpMRFkio yrGbsDy9anQTvaAS0K4RbukmDAoNI6BYkMgFvE3VGY9tRhA0sthaWBVk961VP2RBni2fx0qNAgqMF 3AA/0QAs2C3g+aq91j2RodonXMsrSDZSj1si2zYbOZpEoo/lsgsbybwYU/6bE/h6btT7WEEr1vnUk /l23WCvfHXgt4MCUhpIOzfoy9gF/w75iELWGRYhcG+r7Z6Xrw3+sGxhCNzUFerRwIK17qOXc0MBOH 0hCOQ2u9g==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1i4h3e-0004LW-NT; Mon, 02 Sep 2019 07:47:27 +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 3E523301A76; Mon, 2 Sep 2019 09:46:49 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id CEA3F29B7E7A5; Mon, 2 Sep 2019 09:47:24 +0200 (CEST) Date: Mon, 2 Sep 2019 09:47:24 +0200 From: Peter Zijlstra To: Patrick Bellasi Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, linux-api@vger.kernel.org, cgroups@vger.kernel.org, Ingo Molnar , Tejun Heo , "Rafael J . Wysocki" , Vincent Guittot , Viresh Kumar , Paul Turner , Michal Koutny , Quentin Perret , Dietmar Eggemann , Morten Rasmussen , Juri Lelli , Todd Kjos , Joel Fernandes , Steve Muckle , Suren Baghdasaryan , Alessio Balsini Subject: Re: [PATCH v14 1/6] sched/core: uclamp: Extend CPU's cgroup controller Message-ID: <20190902074724.GP2369@hirez.programming.kicks-ass.net> References: <20190822132811.31294-1-patrick.bellasi@arm.com> <20190822132811.31294-2-patrick.bellasi@arm.com> <20190830094505.GA2369@hirez.programming.kicks-ass.net> <87zhjnnqz2.fsf@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87zhjnnqz2.fsf@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 Mon, Sep 02, 2019 at 07:38:53AM +0100, Patrick Bellasi wrote: > > On Fri, Aug 30, 2019 at 09:45:05 +0000, Peter Zijlstra wrote... > > > On Thu, Aug 22, 2019 at 02:28:06PM +0100, Patrick Bellasi wrote: > >> +#define _POW10(exp) ((unsigned int)1e##exp) > >> +#define POW10(exp) _POW10(exp) > > > > What is this magic? You're forcing a float literal into an integer. > > Surely that deserves a comment! > > Yes, I'm introducing the two constants: > UCLAMP_PERCENT_SHIFT, > UCLAMP_PERCENT_SCALE > similar to what we have for CAPACITY. Moreover, I need both 100*100 (for > the scale) and 100 further down in the code for the: Ooh, right you are. I clearly was in need of weekend. Somehow I read that code as if you were forcing the float representation into an integer, which is not what you do. > percent = div_u64_rem(percent, POW10(UCLAMP_PERCENT_SHIFT), &rem); > > used in cpu_uclamp_print(). > > That's why adding a compile time support to compute a 10^N is useful. > > C provides the "1eN" literal, I just convert it to integer and to do > that at compile time I need a two level macros. > > What if I add this comment just above the macro definitions: > > /* > * Integer 10^N with a given N exponent by casting to integer the literal "1eN" > * C expression. Since there is no way to convert a macro argument (N) into a > * character constant, use two levels of macros. > */ > > is this clear enough? Yeah, let me go add that. > > > >> +struct uclamp_request { > >> +#define UCLAMP_PERCENT_SHIFT 2 > >> +#define UCLAMP_PERCENT_SCALE (100 * POW10(UCLAMP_PERCENT_SHIFT)) > >> + s64 percent; > >> + u64 util; > >> + int ret; > >> +}; > >> + > >> +static inline struct uclamp_request > >> +capacity_from_percent(char *buf) > >> +{ > >> + struct uclamp_request req = { > >> + .percent = UCLAMP_PERCENT_SCALE, > >> + .util = SCHED_CAPACITY_SCALE, > >> + .ret = 0, > >> + }; > >> + > >> + buf = strim(buf); > >> + if (strncmp("max", buf, 4)) { > > > > That is either a bug, and you meant to write: strncmp(buf, "max", 3), > > or it is not, and then you could've written: strcmp(buf, "max") > > I don't think it's a bug. > > The usage of 4 is intentional, to force a '\0' check while using > strncmp(). Otherwise, strncmp(buf, "max", 3) would accept also strings > starting by "max", which we don't want. Right; I figured. > > But as written it doesn't make sense. > > The code is safe but I agree that strcmp() does just the same and it > does not generate confusion. That's actually a pretty good example > on how it's not always better to use strncmp() instead of strcmp(). OK, I made it strcmp(), because that is what I figured was the intended semantics.