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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 5D69BC433E1 for ; Wed, 24 Jun 2020 12:51:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3416320663 for ; Wed, 24 Jun 2020 12:51:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593003081; bh=gN5PKas9CvuWwK/weRNNyuR8Fc9CxY8OZRwT+G269wE=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=ER6t9gnYfOiWlsNMMKDuoz5u3vN13M1nX82SvKykiUrTMBb5QN7IQVWiOZj3uDveF eEZJsEnsj/lHRf4Vsm9oefUmGRwnt28kRFGwrifF22JAiA19IzZGcTfUB/cFKenrus DjKGTb8eFdYUS7P/6vd2/dI/vpRLe/eSxrLF3JCY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390907AbgFXMvT (ORCPT ); Wed, 24 Jun 2020 08:51:19 -0400 Received: from mail-ot1-f66.google.com ([209.85.210.66]:42833 "EHLO mail-ot1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388942AbgFXMvS (ORCPT ); Wed, 24 Jun 2020 08:51:18 -0400 Received: by mail-ot1-f66.google.com with SMTP id t6so1758499otk.9; Wed, 24 Jun 2020 05:51:18 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=P/bkPQJyEuJLLZDCNPTwD8zOfuXTt/HbpVEXhGvvUkU=; b=AI94apMJFjRHFuRxILGcYWcD/kU95W6XXd2KMuZ56rAQHH7lYg5c1easXanf/m/r76 z45CTt6gtMPVFy35cFUBmJQj8bn/gq150S5KxyXhe7KBMm86AkdkWVXRarZdxK0VOVLo l+yka3SSE/uEzlgwpS7NLgWQ1CqUrz5wl538GOMlQ/OMSOJDsTzGpUiO9GUxplW1+4Zh MtX+MXDMEfM0VV1+V8+6/Wc0QLk/7LBx7rf2XhtVwj+UMvJegB8tlid7eLWDO7WDsGRm rLt3KblNMIQ4EdSXlgh3crnmoA+tlFCC9FArFCBn3A3YsacJT9KPk2fUCPzhOvNOTx8l 12bw== X-Gm-Message-State: AOAM533bz9me+GccRnfVXO83Xf/ZjgWRu611+S/nF/w4GgbV+Rht1CU4 KzOSR5GV4PLZEbBxT36Q7aqZP4PAQ4ny2PQno0Y= X-Google-Smtp-Source: ABdhPJyJaj4dGUTvhHBRNMjHUnZdGheAZvOfYIAiAj6lGBGPOY3/8KAhD1pS066Sr/l31WOleOmCuvjLIX/i+LSdSPM= X-Received: by 2002:a9d:7d15:: with SMTP id v21mr21740160otn.118.1593003077552; Wed, 24 Jun 2020 05:51:17 -0700 (PDT) MIME-Version: 1.0 References: <20200623142138.209513-1-qperret@google.com> <20200623142138.209513-3-qperret@google.com> <20200624055023.xofefhohf7wifme5@vireshk-i7> In-Reply-To: <20200624055023.xofefhohf7wifme5@vireshk-i7> From: "Rafael J. Wysocki" Date: Wed, 24 Jun 2020 14:51:04 +0200 Message-ID: Subject: Re: [PATCH v2 2/2] cpufreq: Specify default governor on command line To: Viresh Kumar Cc: Quentin Perret , "Rafael J. Wysocki" , "Rafael J. Wysocki" , Arnd Bergmann , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , linuxppc-dev , Linux Kernel Mailing List , Linux PM , "Cc: Android Kernel" , Todd Kjos , adharmap@codeaurora.org Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 24, 2020 at 7:50 AM Viresh Kumar wrote: > > On 23-06-20, 15:21, Quentin Perret wrote: > > Currently, the only way to specify the default CPUfreq governor is via > > Kconfig options, which suits users who can build the kernel themselves > > perfectly. > > > > However, for those who use a distro-like kernel (such as Android, with > > the Generic Kernel Image project), the only way to use a different > > default is to boot to userspace, and to then switch using the sysfs > > interface. Being able to specify the default governor on the command > > line, like is the case for cpuidle, would enable those users to specify > > their governor of choice earlier on, and to simplify slighlty the > > userspace boot procedure. > > > > To support this use-case, add a kernel command line parameter enabling > > to specify a default governor for CPUfreq, which takes precedence over > > the builtin default. > > > > This implementation has one notable limitation: the default governor > > must be registered before the driver. This is solved for builtin > > governors and drivers using appropriate *_initcall() functions. And in > > the modular case, this must be reflected as a constraint on the module > > loading order. > > > > Signed-off-by: Quentin Perret > > --- > > .../admin-guide/kernel-parameters.txt | 5 ++++ > > Documentation/admin-guide/pm/cpufreq.rst | 6 ++--- > > drivers/cpufreq/cpufreq.c | 23 +++++++++++++++---- > > 3 files changed, 26 insertions(+), 8 deletions(-) > > > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > > index fb95fad81c79..5fd3c9f187eb 100644 > > --- a/Documentation/admin-guide/kernel-parameters.txt > > +++ b/Documentation/admin-guide/kernel-parameters.txt > > @@ -703,6 +703,11 @@ > > cpufreq.off=1 [CPU_FREQ] > > disable the cpufreq sub-system > > > > + cpufreq.default_governor= > > + [CPU_FREQ] Name of the default cpufreq governor to use. > > + This governor must be registered in the kernel before > > + the cpufreq driver probes. > > + > > cpu_init_udelay=N > > [X86] Delay for N microsec between assert and de-assert > > of APIC INIT to start processors. This delay occurs > > diff --git a/Documentation/admin-guide/pm/cpufreq.rst b/Documentation/admin-guide/pm/cpufreq.rst > > index 0c74a7784964..368e612145d2 100644 > > --- a/Documentation/admin-guide/pm/cpufreq.rst > > +++ b/Documentation/admin-guide/pm/cpufreq.rst > > @@ -147,9 +147,9 @@ CPUs in it. > > > > The next major initialization step for a new policy object is to attach a > > scaling governor to it (to begin with, that is the default scaling governor > > -determined by the kernel configuration, but it may be changed later > > -via ``sysfs``). First, a pointer to the new policy object is passed to the > > -governor's ``->init()`` callback which is expected to initialize all of the > > +determined by the kernel command line or configuration, but it may be changed > > +later via ``sysfs``). First, a pointer to the new policy object is passed to > > +the governor's ``->init()`` callback which is expected to initialize all of the > > data structures necessary to handle the given policy and, possibly, to add > > a governor ``sysfs`` interface to it. Next, the governor is started by > > invoking its ``->start()`` callback. > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > > index 0128de3603df..4b1a5c0173cf 100644 > > --- a/drivers/cpufreq/cpufreq.c > > +++ b/drivers/cpufreq/cpufreq.c > > @@ -50,6 +50,9 @@ static LIST_HEAD(cpufreq_governor_list); > > #define for_each_governor(__governor) \ > > list_for_each_entry(__governor, &cpufreq_governor_list, governor_list) > > > > +static char cpufreq_param_governor[CPUFREQ_NAME_LEN]; > > +static struct cpufreq_governor *default_governor; > > + > > /** > > * The "cpufreq driver" - the arch- or hardware-dependent low > > * level driver of CPUFreq support, and its spinlock. This lock > > @@ -1055,7 +1058,6 @@ __weak struct cpufreq_governor *cpufreq_default_governor(void) > > > > static int cpufreq_init_policy(struct cpufreq_policy *policy) > > { > > - struct cpufreq_governor *def_gov = cpufreq_default_governor(); > > struct cpufreq_governor *gov = NULL; > > unsigned int pol = CPUFREQ_POLICY_UNKNOWN; > > > > @@ -1065,8 +1067,8 @@ static int cpufreq_init_policy(struct cpufreq_policy *policy) > > if (gov) { > > pr_debug("Restoring governor %s for cpu %d\n", > > policy->governor->name, policy->cpu); > > - } else if (def_gov) { > > - gov = def_gov; > > + } else if (default_governor) { > > + gov = default_governor; > > } else { > > return -ENODATA; > > } > > @@ -1074,8 +1076,8 @@ static int cpufreq_init_policy(struct cpufreq_policy *policy) > > /* Use the default policy if there is no last_policy. */ > > if (policy->last_policy) { > > pol = policy->last_policy; > > - } else if (def_gov) { > > - pol = cpufreq_parse_policy(def_gov->name); > > + } else if (default_governor) { > > + pol = cpufreq_parse_policy(default_governor->name); > > /* > > * In case the default governor is neiter "performance" > > * nor "powersave", fall back to the initial policy > > @@ -2320,6 +2322,9 @@ int cpufreq_register_governor(struct cpufreq_governor *governor) > > list_add(&governor->governor_list, &cpufreq_governor_list); > > } > > > > + if (!strncasecmp(cpufreq_param_governor, governor->name, CPUFREQ_NAME_LEN)) > > + default_governor = governor; > > + > > mutex_unlock(&cpufreq_governor_mutex); > > return err; > > } > > @@ -2348,6 +2353,8 @@ void cpufreq_unregister_governor(struct cpufreq_governor *governor) > > > > mutex_lock(&cpufreq_governor_mutex); > > list_del(&governor->governor_list); > > + if (governor == default_governor) > > + default_governor = cpufreq_default_governor(); > > mutex_unlock(&cpufreq_governor_mutex); > > } > > EXPORT_SYMBOL_GPL(cpufreq_unregister_governor); > > @@ -2789,7 +2796,13 @@ static int __init cpufreq_core_init(void) > > cpufreq_global_kobject = kobject_create_and_add("cpufreq", &cpu_subsys.dev_root->kobj); > > BUG_ON(!cpufreq_global_kobject); > > > > + mutex_lock(&cpufreq_governor_mutex); > > + if (!default_governor) > > + default_governor = cpufreq_default_governor(); > > + mutex_unlock(&cpufreq_governor_mutex); > > I don't think locking is required here at core-initcall level. It isn't necessary AFAICS, but it may as well be regarded as annotation (kind of instead of having a comment explaining why it need not be used).