From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759061AbbKSTHk (ORCPT ); Thu, 19 Nov 2015 14:07:40 -0500 Received: from mx1.redhat.com ([209.132.183.28]:52370 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759015AbbKSTHj (ORCPT ); Thu, 19 Nov 2015 14:07:39 -0500 Message-ID: <564E1DF9.1020809@redhat.com> Date: Thu, 19 Nov 2015 14:07:37 -0500 From: Prarit Bhargava User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Viresh Kumar CC: linux-kernel@vger.kernel.org, Srinivas Pandruvada , Len Brown , Alexandra Yates , Kristen Carlson Accardi , "Rafael J. Wysocki" , linux-pm@vger.kernel.org Subject: Re: [PATCH] cpufreq, intel_pstate.c, Fix rounding errors References: <1447862144-7188-1-git-send-email-prarit@redhat.com> <20151119044639.GD3737@ubuntu> In-Reply-To: <20151119044639.GD3737@ubuntu> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/18/2015 11:46 PM, Viresh Kumar wrote: > On 18-11-15, 10:55, Prarit Bhargava wrote: >> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c >> index 2e31d09..686f024 100644 >> --- a/drivers/cpufreq/intel_pstate.c >> +++ b/drivers/cpufreq/intel_pstate.c >> @@ -1233,6 +1233,8 @@ static int intel_pstate_set_policy(struct cpufreq_policy *policy) >> struct cpudata *cpu; >> int i; >> #endif >> + int max_policy_calc; >> + >> pr_debug("intel_pstate: %s max %u policy->max %u\n", __func__, >> policy->cpuinfo.max_freq, policy->max); >> if (!policy->cpuinfo.max_freq) >> @@ -1249,7 +1251,10 @@ static int intel_pstate_set_policy(struct cpufreq_policy *policy) >> limits = &powersave_limits; >> limits->min_policy_pct = (policy->min * 100) / policy->cpuinfo.max_freq; >> limits->min_policy_pct = clamp_t(int, limits->min_policy_pct, 0 , 100); >> - limits->max_policy_pct = (policy->max * 100) / policy->cpuinfo.max_freq; >> + >> + max_policy_calc = (policy->max * 1000) / policy->cpuinfo.max_freq; >> + limits->max_policy_pct = DIV_ROUND_UP(max_policy_calc, 10); >> + > > Nice catch, but why can't we do this instead: > > limits->max_policy_pct = DIV_ROUND_UP(policy->max * 100, policy->cpuinfo.max_freq); > Ah, I got so deep into the code I didn't even think of simplifying the calculation. Thanks -- I'll do that instead. >> limits->max_policy_pct = clamp_t(int, limits->max_policy_pct, 0 , 100); >> >> /* Normalize user input to [min_policy_pct, max_policy_pct] */ >> @@ -1269,6 +1274,7 @@ static int intel_pstate_set_policy(struct cpufreq_policy *policy) >> int_tofp(100)); >> limits->max_perf = div_fp(int_tofp(limits->max_perf_pct), >> int_tofp(100)); >> + limits->max_perf = round_up(limits->max_perf, 8); > > Perhaps you should fix this in a separate patch. > Okay, I submit these as a 2 part patchset. P.