From patchwork Tue Jan 11 15:54:19 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Pierre Gondois X-Patchwork-Id: 531706 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2D73BC433F5 for ; Tue, 11 Jan 2022 15:54:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343654AbiAKPym (ORCPT ); Tue, 11 Jan 2022 10:54:42 -0500 Received: from foss.arm.com ([217.140.110.172]:48650 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1349717AbiAKPym (ORCPT ); Tue, 11 Jan 2022 10:54:42 -0500 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 21C826D; Tue, 11 Jan 2022 07:54:42 -0800 (PST) Received: from e126645.arm.com (unknown [10.57.67.22]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 42BA23F774; Tue, 11 Jan 2022 07:54:40 -0800 (PST) From: Pierre Gondois To: linux-kernel@vger.kernel.org Cc: Ionela.Voinescu@arm.com, Lukasz Luba , Morten Rasmussen , "Rafael J. Wysocki" , Viresh Kumar , linux-pm@vger.kernel.org Subject: [PATCH v2] cpufreq: CPPC: Fix performance/frequency conversion Date: Tue, 11 Jan 2022 16:54:19 +0100 Message-Id: <20220111155419.943980-1-Pierre.Gondois@arm.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-pm@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: 1- the functions are not inverse for some values: (perf_to_khz(khz_to_perf(x)) != x) 2- cppc_cpufreq_perf_to_khz(LOWEST_PERF) can sometimes give a different value from LOWEST_FREQ due to integer approximation 3- it is implied that performance and frequency are proportional (NOMINAL_FREQ / NOMINAL_PERF) == (LOWEST_PERF / LOWEST_FREQ) This patch changes the conversion functions to an affine function. This fixes the 3 points above. Suggested-by: Lukasz Luba Suggested-by: Morten Rasmussen Signed-off-by: Pierre Gondois --- drivers/cpufreq/cppc_cpufreq.c | 43 +++++++++++++++++----------------- 1 file changed, 21 insertions(+), 22 deletions(-) diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c index db17196266e4..5024d9af2e6e 100644 --- a/drivers/cpufreq/cppc_cpufreq.c +++ b/drivers/cpufreq/cppc_cpufreq.c @@ -303,52 +303,48 @@ 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 + * use them to convert perf to freq and vice versa. The conversion is + * extrapolated as an affine function passing by the 2 points: + * - (Low perf, Low freq) + * - (Nominal perf, Nominal perf) */ static unsigned int cppc_cpufreq_perf_to_khz(struct cppc_cpudata *cpu_data, unsigned int perf) { struct cppc_perf_caps *caps = &cpu_data->perf_caps; + s64 retval, offset = 0; 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; - } + mul = caps->nominal_freq - caps->lowest_freq; + div = caps->nominal_perf - caps->lowest_perf; + offset = caps->nominal_freq - (u64)caps->nominal_perf * mul / div; } else { if (!max_khz) max_khz = cppc_get_dmi_max_khz(); mul = max_khz; div = caps->highest_perf; } - return (u64)perf * mul / div; + + retval = offset + (u64)perf * mul / div; + if (retval >= 0) + return retval; + return 0; } static unsigned int cppc_cpufreq_khz_to_perf(struct cppc_cpudata *cpu_data, unsigned int freq) { struct cppc_perf_caps *caps = &cpu_data->perf_caps; + s64 retval, offset = 0; 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; - } + mul = caps->nominal_perf - caps->lowest_perf; + div = caps->nominal_freq - caps->lowest_freq; + offset = caps->nominal_perf - (u64)caps->nominal_freq * mul / div; } else { if (!max_khz) max_khz = cppc_get_dmi_max_khz(); @@ -356,7 +352,10 @@ static unsigned int cppc_cpufreq_khz_to_perf(struct cppc_cpudata *cpu_data, div = max_khz; } - return (u64)freq * mul / div; + retval = offset + (u64)freq * mul / div; + if (retval >= 0) + return retval; + return 0; } static int cppc_cpufreq_set_target(struct cpufreq_policy *policy,