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 <qper...@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. Apart from that: Acked-by: Viresh Kumar <viresh.ku...@linaro.org> > + > return 0; > } > module_param(off, int, 0444); > +module_param_string(default_governor, cpufreq_param_governor, > CPUFREQ_NAME_LEN, 0444); > core_initcall(cpufreq_core_init); > -- > 2.27.0.111.gc72c7da667-goog -- viresh