Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Wed, 24 Jun 2020 14:51:04 +0200 | Subject | Re: [PATCH v2 2/2] cpufreq: Specify default governor on command line |
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On Wed, Jun 24, 2020 at 7:50 AM Viresh Kumar <viresh.kumar@linaro.org> 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 <qperret@google.com> > > --- > > .../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).
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