From 10cbfd68e2ff5bb562f57df2895400d7534a1a10 Mon Sep 17 00:00:00 2001 From: Michael Turquette Date: Tue, 30 Jun 2015 12:45:27 +0100 Subject: [PATCH] cpufreq: introduce cpufreq_driver_is_slow Some architectures and platforms perform CPU frequency transitions through a non-blocking method, while some might block or sleep. Even when frequency transitions do not block or sleep they may be very slow. This distinction is important when trying to change frequency from a non-interruptible context in a scheduler hot path. Describe this distinction with a cpufreq driver flag, CPUFREQ_DRIVER_FAST. The default is to not have this flag set, thus erring on the side of caution. cpufreq_driver_is_slow() is also introduced in this patch. Setting the above flag will allow this function to return false. [smuckle@linaro.org: change flag/API to include drivers that are too slow for scheduler hot paths, in addition to those that block/sleep] Cc: Rafael J. Wysocki Cc: Viresh Kumar Signed-off-by: Michael Turquette Signed-off-by: Steve Muckle --- drivers/cpufreq/cpufreq.c | 6 ++++++ include/linux/cpufreq.h | 9 +++++++++ 2 files changed, 15 insertions(+) diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index e5aa57b27d06..2b99bc305040 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -154,6 +154,12 @@ bool have_governor_per_policy(void) } EXPORT_SYMBOL_GPL(have_governor_per_policy); +bool cpufreq_driver_is_slow(void) +{ + return !(cpufreq_driver->flags & CPUFREQ_DRIVER_FAST); +} +EXPORT_SYMBOL_GPL(cpufreq_driver_is_slow); + struct kobject *get_governor_parent_kobj(struct cpufreq_policy *policy) { if (have_governor_per_policy()) diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h index 89e8e04aa73b..f9bb7039740c 100644 --- a/include/linux/cpufreq.h +++ b/include/linux/cpufreq.h @@ -160,6 +160,7 @@ u64 get_cpu_idle_time(unsigned int cpu, u64 *wall, int io_busy); int cpufreq_get_policy(struct cpufreq_policy *policy, unsigned int cpu); int cpufreq_update_policy(unsigned int cpu); bool have_governor_per_policy(void); +bool cpufreq_driver_is_slow(void); struct kobject *get_governor_parent_kobj(struct cpufreq_policy *policy); #else static inline unsigned int cpufreq_get(unsigned int cpu) @@ -317,6 +318,14 @@ struct cpufreq_driver { */ #define CPUFREQ_NEED_INITIAL_FREQ_CHECK (1 << 5) +/* + * Indicates that it is safe to call cpufreq_driver_target from + * non-interruptable context in scheduler hot paths. Drivers must + * opt-in to this flag, as the safe default is that they might sleep + * or be too slow for hot path use. + */ +#define CPUFREQ_DRIVER_FAST (1 << 6) + int cpufreq_register_driver(struct cpufreq_driver *driver_data); int cpufreq_unregister_driver(struct cpufreq_driver *driver_data); -- 2.34.1