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,URIBL_BLOCKED, 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 996C8C43387 for ; Fri, 18 Jan 2019 16:16:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5F61320850 for ; Fri, 18 Jan 2019 16:16:28 +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="vPUmQTyo" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728210AbfARQQ0 (ORCPT ); Fri, 18 Jan 2019 11:16:26 -0500 Received: from merlin.infradead.org ([205.233.59.134]:33800 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727241AbfARQQ0 (ORCPT ); Fri, 18 Jan 2019 11:16:26 -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=8J0KEgksINfaZwZNgj6ZCNAGBR3wkWZqqcLlb6hhP/E=; b=vPUmQTyoS8r9xPbjTsgvLC4f5 6PyhG9WFkJZllxljlHBMpQVpKMBa7fI3wOgzujeTEyn9GRbIy/qlq3slvLrGyueoaFriIG07f7OmR CU9aLkCqZ9VzchYmENm68HI67jhGzjWrSkNAwqCnR4iKwNFJtZ3hrbQsQf9Ltj1ZpHpyoNSbjXnES CldzsuMFhs08RUb3mR6WPONlrF/bS1PNltQ/QcpMMovfHDBBWktEtt7xsCMZuNaRmhbzxzanpf0qP sHtO4XKN7y5U+2tnKvengidENL9TULbN61kTLMSyryvr6LjEutvXbfSZG0buBYYr+vUtrYV7HBn/k p3llGvTRg==; Received: from [89.200.44.227] (helo=worktop.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1gkWob-00046w-VG; Fri, 18 Jan 2019 16:16:18 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id 4454B9818FF; Fri, 18 Jan 2019 17:16:16 +0100 (CET) Date: Fri, 18 Jan 2019 17:16:16 +0100 From: Peter Zijlstra To: Chunyan Zhang Cc: Ingo Molnar , Vincent Wang , Quentin Perret , linux-kernel@vger.kernel.org, Chunyan Zhang Subject: Re: [PATCH V2] sched/cpufreq: calculate util / cap in advance in map_util_freq() Message-ID: <20190118161616.GH14054@worktop.programming.kicks-ass.net> References: <1547089325-15691-1-git-send-email-chunyan.zhang@unisoc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1547089325-15691-1-git-send-email-chunyan.zhang@unisoc.com> 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 10, 2019 at 11:02:05AM +0800, Chunyan Zhang wrote: > From: Vincent Wang > > When a task that is in_iowait state is enqueued, cpufreq_update_util() > will be invoked with SCHED_CPUFREQ_IOWAIT flag. In this case,the value > of util and cap, which are parameters used in map_util_freq(), will be > cpu frequency, instead of cpu util and capactiy. > > For some 32bit architectures, the size of unsigned long is 32. When > calculating freq, there may be an overflow error in this expression: Would it not be much better to fix that one case instead of adding extra instructions for everyone all the time?