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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CB421C433FE for ; Fri, 22 Oct 2021 07:51:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B030760EB8 for ; Fri, 22 Oct 2021 07:51:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232220AbhJVHxh (ORCPT ); Fri, 22 Oct 2021 03:53:37 -0400 Received: from foss.arm.com ([217.140.110.172]:50924 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231773AbhJVHxf (ORCPT ); Fri, 22 Oct 2021 03:53:35 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 651C21FB; Fri, 22 Oct 2021 00:51:18 -0700 (PDT) Received: from e120189.home (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 554903F70D; Fri, 22 Oct 2021 00:51:15 -0700 (PDT) From: Pierre Gondois To: Ionela.Voinescu@arm.com, Lukasz.Luba@arm.com, Morten.Rasmussen@arm.com, "Rafael J. Wysocki" , Viresh Kumar , linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Dietmar.Eggemann@arm.com Subject: [PATCH v1] cpufreq: CPPC: Fix performance/frequency conversion Date: Fri, 22 Oct 2021 08:50:57 +0100 Message-Id: <20211022075057.10759-1-Pierre.Gondois@arm.com> X-Mailer: git-send-email 2.17.1 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org CPUfreq governors request CPU frequencies using information on current CPU usage. The CPPC driver converts them to performance requests. Frequency targets are computed as: target_freq = (util / cpu_capacity) * max_freq target_freq is then clamped between [policy->min, policy->max]. The CPPC driver converts performance values to frequencies (and vice-versa) using cppc_cpufreq_perf_to_khz() and cppc_cpufreq_khz_to_perf(). These functions both use two different factors depending on the range of the input value. For cppc_cpufreq_khz_to_perf(): - (NOMINAL_PERF / NOMINAL_FREQ) or - (LOWEST_PERF / LOWEST_FREQ) and for cppc_cpufreq_perf_to_khz(): - (NOMINAL_FREQ / NOMINAL_PERF) or - ((NOMINAL_PERF - LOWEST_FREQ) / (NOMINAL_PERF - LOWEST_PERF)) This means the functions are not inverse for some values: (perf_to_khz(khz_to_perf(x)) != x) This patch makes use of one single conversion factor, being (MAX_PERF / MAX_FREQ). As LOWEST_FREQ is not used during conversion, the LOWEST_FREQ advertised through policy->cpuinfo.min_freq might be different from the LOWEST_FREQ value available in the CPPC object, but the conversion will be correct. Suggested-by: Lukasz Luba Suggested-by: Morten Rasmussen Signed-off-by: Pierre Gondois --- drivers/cpufreq/cppc_cpufreq.c | 33 ++++++++++----------------------- 1 file changed, 10 insertions(+), 23 deletions(-) diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c index d4c27022b9c9..d2ac74e7701e 100644 --- a/drivers/cpufreq/cppc_cpufreq.c +++ b/drivers/cpufreq/cppc_cpufreq.c @@ -302,13 +302,10 @@ static u64 cppc_get_dmi_max_khz(void) } /* - * If CPPC lowest_freq and nominal_freq registers are exposed then we can - * use them to convert perf to freq and vice versa - * - * If the perf/freq point lies between Nominal and Lowest, we can treat - * (Low perf, Low freq) and (Nom Perf, Nom freq) as 2D co-ordinates of a line - * and extrapolate the rest - * For perf/freq > Nominal, we use the ratio perf:freq at Nominal for conversion + * The CPPC driver receives frequency requests and translates them to performance + * requests. Thus, frequency values are actually performance values on a frequency + * scale. The conversion is done as: + * target_freq = target_perf * (nominal_freq / nominal_perf) */ static unsigned int cppc_cpufreq_perf_to_khz(struct cppc_cpudata *cpu_data, unsigned int perf) @@ -317,14 +314,9 @@ static unsigned int cppc_cpufreq_perf_to_khz(struct cppc_cpudata *cpu_data, static u64 max_khz; u64 mul, div; - if (caps->lowest_freq && caps->nominal_freq) { - if (perf >= caps->nominal_perf) { - mul = caps->nominal_freq; - div = caps->nominal_perf; - } else { - mul = caps->nominal_freq - caps->lowest_freq; - div = caps->nominal_perf - caps->lowest_perf; - } + if (caps->nominal_freq) { + mul = caps->nominal_freq; + div = caps->nominal_perf; } else { if (!max_khz) max_khz = cppc_get_dmi_max_khz(); @@ -341,14 +333,9 @@ static unsigned int cppc_cpufreq_khz_to_perf(struct cppc_cpudata *cpu_data, static u64 max_khz; u64 mul, div; - if (caps->lowest_freq && caps->nominal_freq) { - if (freq >= caps->nominal_freq) { - mul = caps->nominal_perf; - div = caps->nominal_freq; - } else { - mul = caps->lowest_perf; - div = caps->lowest_freq; - } + if (caps->nominal_freq) { + mul = caps->nominal_perf; + div = caps->nominal_freq; } else { if (!max_khz) max_khz = cppc_get_dmi_max_khz(); -- 2.17.1