Re: [PATCH v2 4/7] cpufreq: report whether cpufreq supports Frequency Invariance (FI)

Rafael J. Wysocki
2020-07-27T14:04:18Z

On Wed, Jul 22, 2020 at 11:38 AM Ionela Voinescu
<ionela.voinescu@arm.com> wrote:
>
> Now that the update of the FI scale factor is done in cpufreq core for
> selected functions - target(), target_index() and fast_switch(),
> we can provide feedback to the task scheduler and architecture code
> on whether cpufreq supports FI.
>
> For this purpose, provide error and debug messages, together with an
> external function to expose whether the cpufreq drivers support FI, by
> using a static key.
>
> The logic behind the enablement of cpufreq-based invariance is as
> follows:
> - cpufreq-based invariance is disabled by default
> - cpufreq-based invariance is enabled if any of the callbacks
> above is implemented while the unsupported setpolicy() is not
> - if enabled, cpufreq-based invariance will be disabled during the
> call of the default arch_set_freq_scale() function which does
> not set a scale factor.
>
> Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>
> Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
> Cc: Viresh Kumar <viresh.kumar@linaro.org>
> ---
> drivers/cpufreq/cpufreq.c | 28 ++++++++++++++++++++++++++++
> include/linux/cpufreq.h | 5 +++++
> 2 files changed, 33 insertions(+)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 3497c1cd6818..1d0b046fe8e9 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -61,6 +61,9 @@ static struct cpufreq_driver *cpufreq_driver;
> static DEFINE_PER_CPU(struct cpufreq_policy *, cpufreq_cpu_data);
> static DEFINE_RWLOCK(cpufreq_driver_lock);
>
> +/* Mark support for the scheduler's frequency invariance engine */
> +static DEFINE_STATIC_KEY_FALSE(cpufreq_set_freq_scale);
> +
> /* Flag to suspend/resume CPUFreq governors */
> static bool cpufreq_suspended;
>
> @@ -69,6 +72,25 @@ static inline bool has_target(void)
> return cpufreq_driver->target_index || cpufreq_driver->target;
> }
>
> +static inline
> +void enable_cpufreq_freq_invariance(struct cpufreq_driver *driver)
> +{
> + if ((driver->target || driver->target_index || driver->fast_switch) &&
> + !driver->setpolicy) {
> +
> + static_branch_enable_cpuslocked(&cpufreq_set_freq_scale);
> + pr_debug("%s: Driver %s can provide frequency invariance.",
> + __func__, driver->name);
> + } else
> + pr_err("%s: Driver %s cannot provide frequency invariance.",
> + __func__, driver->name);

This doesn't follow the kernel coding style (the braces around the
pr_err() statement are missing).

Besides, IMO on architectures where arch_set_freq_scale() is empty,
this should be empty as well.

> +}
> +
> +bool cpufreq_sets_freq_scale(void)
> +{
> + return static_branch_likely(&cpufreq_set_freq_scale);
> +}
> +
> /* internal prototypes */
> static unsigned int __cpufreq_get(struct cpufreq_policy *policy);
> static int cpufreq_init_governor(struct cpufreq_policy *policy);
> @@ -159,6 +181,9 @@ EXPORT_SYMBOL_GPL(get_cpu_idle_time);
> __weak void arch_set_freq_scale(struct cpumask *cpus, unsigned long cur_freq,
> unsigned long max_freq)
> {
> + if (cpufreq_sets_freq_scale())
> + static_branch_disable_cpuslocked(&cpufreq_set_freq_scale);
> +
> }
> EXPORT_SYMBOL_GPL(arch_set_freq_scale);
>
> @@ -2722,6 +2747,8 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
> cpufreq_driver = driver_data;
> write_unlock_irqrestore(&cpufreq_driver_lock, flags);
>
> + enable_cpufreq_freq_invariance(cpufreq_driver);
> +
> if (driver_data->setpolicy)
> driver_data->flags |= CPUFREQ_CONST_LOOPS;
>
> @@ -2791,6 +2818,7 @@ int cpufreq_unregister_driver(struct cpufreq_driver *driver)
> cpus_read_lock();
> subsys_interface_unregister(&cpufreq_interface);
> remove_boost_sysfs_file();
> + static_branch_disable_cpuslocked(&cpufreq_set_freq_scale);
> cpuhp_remove_state_nocalls_cpuslocked(hp_online);
>
> write_lock_irqsave(&cpufreq_driver_lock, flags);
> diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> index e62b022cb07e..f81215ad76f1 100644
> --- a/include/linux/cpufreq.h
> +++ b/include/linux/cpufreq.h
> @@ -217,6 +217,7 @@ void refresh_frequency_limits(struct cpufreq_policy *policy);
> void cpufreq_update_policy(unsigned int cpu);
> void cpufreq_update_limits(unsigned int cpu);
> bool have_governor_per_policy(void);
> +bool cpufreq_sets_freq_scale(void);
> struct kobject *get_governor_parent_kobj(struct cpufreq_policy *policy);
> void cpufreq_enable_fast_switch(struct cpufreq_policy *policy);
> void cpufreq_disable_fast_switch(struct cpufreq_policy *policy);
> @@ -237,6 +238,10 @@ static inline unsigned int cpufreq_get_hw_max_freq(unsigned int cpu)
> {
> return 0;
> }
> +static inline bool cpufreq_sets_freq_scale(void)
> +{
> + return false;
> +}
> static inline void disable_cpufreq(void) { }
> #endif
>
> --
> 2.17.1