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 A8F6EC433EF for ; Fri, 5 Nov 2021 15:40:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9059A6125F for ; Fri, 5 Nov 2021 15:40:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231352AbhKEPnU (ORCPT ); Fri, 5 Nov 2021 11:43:20 -0400 Received: from mail-oi1-f182.google.com ([209.85.167.182]:33416 "EHLO mail-oi1-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233625AbhKEPnP (ORCPT ); Fri, 5 Nov 2021 11:43:15 -0400 Received: by mail-oi1-f182.google.com with SMTP id bl27so12251035oib.0; Fri, 05 Nov 2021 08:40:35 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=+aMNxNbmpqOJ7wYtvnDP1I1JUU/Vwc9pDw9R9dCWQ44=; b=vaOaWAiEfBFJqtU4VEou2yq40L7FbHZhG0orjk7Afxa0bfnM0P9e4Vt7zjltUbb5FI 6bV+0yyK1tiuCq3V5fmsrs5w7AZfv3MuLmoQOThRYq0wPAOQ/G/WZZ5uS3iuXS+kkZRU niMk6TBshGu3/8fXiS6h0SzMOFXigO3jGAtw4DzFB4c8r3aszGZia07mUNc+fKkbJSu0 6gTy9zzDoTuKO35vjnoiswrpnYP2q/NIcZXBnm5kMx+eoPO8kkyK42xHePL7d3/hCeOY BCUzKG4ZvH9w6a03sYX/F4Blk9UnppTEzFN59j97vcWbwt2TGDt6E6SL2MnBB6iOuVj6 XZzA== X-Gm-Message-State: AOAM532o8as1kz47jkdDWzFZxNdlUHrXBWmdwwJSUp8h5HznZ+WRIn2g xRINsGArhRz3WX6JzCjqzeSTPdm2JZSpdaT4NxQ= X-Google-Smtp-Source: ABdhPJyc7w0NC5gvnKZJhWB4Hi7WOpvPTSAuWUqtQbakK/6zRNwCBktNVWVPjvoGCL0SjsOFomAK54mlVnTp8moDgGo= X-Received: by 2002:a05:6808:e90:: with SMTP id k16mr22209764oil.166.1636126835039; Fri, 05 Nov 2021 08:40:35 -0700 (PDT) MIME-Version: 1.0 References: <20211022075057.10759-1-Pierre.Gondois@arm.com> In-Reply-To: <20211022075057.10759-1-Pierre.Gondois@arm.com> From: "Rafael J. Wysocki" Date: Fri, 5 Nov 2021 16:40:24 +0100 Message-ID: Subject: Re: [PATCH v1] cpufreq: CPPC: Fix performance/frequency conversion To: Pierre Gondois Cc: Ionela Voinescu , Lukasz Luba , Morten Rasmussen , "Rafael J. Wysocki" , Viresh Kumar , Linux PM , Linux Kernel Mailing List , Dietmar Eggemann Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 22, 2021 at 9:51 AM Pierre Gondois wrote: > > 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. Well, this assumes that there is a linear perf <-> freq mapping which is a change in behavior. While I agree that consistency is a good thing in general, won't this cause the values visible via sysfs to change? And if it does, won't it confuse anyone or break anything in user space? > 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 >