之前看过interactive调度器，对应的还有ondemand、performance等调度器，调度器是上层策略，而调度器的实现则是通过policy来实现的。
policy
Governor是调频的上层策略, policy是一次调频操作的实体 (句柄), 一个policy可以与多个cpu对应.
struct cpufreq_policy {
/* CPUs sharing clock, require sw coordination(协调) */
cpumask_var_t cpus; /* Online CPUs only */
cpumask_var_t related_cpus; /* Online + Offline CPUs */
cpumask_var_t real_cpus; /* Related and present */
unsigned int shared_type; /* ACPI: ANY or ALL affected CPUs
should set cpufreq */
// policy的managed cpu号. 一般为注册policy的cpu; 当该cpu offline时,
// 会选取cpus的下一cpu作为新的managed cpu. 此时前面的cpu称为last_cpu.
unsigned int cpu; /* cpu managing this policy, must be online */
struct clk *clk;
// 硬件特性
struct cpufreq_cpuinfo cpuinfo;/* see above */
// 软件特性
unsigned int min; /* in kHz */
unsigned int max; /* in kHz */
unsigned int cur; /* in kHz, only needed if cpufreq
* governors are used */
// 类似变频之前的freq和目标freq
unsigned int restore_freq; /* = policy->cur before transition */
unsigned int target_freq; /* freq that the policy wants to set */
unsigned int suspend_freq; /* freq to set during suspend */
unsigned int policy; /* see above */
unsigned int last_policy; /* policy before unplug(拔核) */
// 当前使用的governor，governor_data是tuables，governor_enabled是witch开关
struct cpufreq_governor *governor; /* see below */
void *governor_data;
bool governor_enabled; /* governor start/stop flag */
// 因为governor是可以切换的
char last_governor[CPUFREQ_NAME_LEN]; /* last governor used */
struct work_struct update; /* if update_policy() needs to be
* called, but you're in IRQ context */
// user_policy一般用于保存原始参数，因为温度过高的时候最大频率可能会发生变化
struct cpufreq_user_policy user_policy;
struct cpufreq_frequency_table *freq_table;
struct list_head policy_list;
struct kobject kobj;
struct completion kobj_unregister;
struct notifier_block pm_qos_freq_nb;
/*
* The rules for this semaphore:
* - Any routine that wants to read from the policy structure will
* do a down_read on this semaphore.
* - Any routine that will write to the policy structure and/or may take away
* the policy altogether (eg. CPU hotplug), will hold this lock in write
* mode before doing so.
*
* Additional rules:
* - Lock should not be held across
* __cpufreq_governor(data, CPUFREQ_GOV_POLICY_EXIT);
*/
struct rw_semaphore rwsem;（信号量）
/*
* Fast switch flags:
* - fast_switch_possible should be set by the driver if it can
* guarantee that frequency can be changed on any CPU sharing the
* policy and that the change will affect all of the policy CPUs then.
* - fast_switch_enabled is to be set by governors that support fast
* freqnency switching with the help of cpufreq_enable_fast_switch().
*/
bool fast_switch_possible;
bool fast_switch_enabled;
/*
* Preferred average time interval between consecutive invocations of
* the driver to set the frequency for this policy. To be set by the
* scaling driver (0, which is the default, means no preference).
*/
unsigned int up_transition_delay_us;
unsigned int down_transition_delay_us;
/* Cached frequency lookup from cpufreq_driver_resolve_freq. */
unsigned int cached_target_freq;
int cached_resolved_idx;
/* Synchronization for frequency transitions */
bool transition_ongoing; /* Tracks transition status */
spinlock_t transition_lock;
wait_queue_head_t transition_wait;
struct task_struct *transition_task; /* Task which is doing the transition */
/* cpufreq-stats */
// 对应的是stat这个节点
struct cpufreq_stats *stats;
/* For cpufreq driver's internal use */
void *driver_data;
};其中
struct cpufreq_cpuinfo {
// 硬件特性
unsigned int max_freq;
unsigned int min_freq;
/* in 10^(-9) s = nanoseconds */纳秒为单位
unsigned int transition_latency;
};struct cpufreq_user_policy {
unsigned int min; /* in kHz */
unsigned int max; /* in kHz */
};struct cpufreq_governor {
char name[CPUFREQ_NAME_LEN];
int initialized;
//指向一个回调函数，CPUFreq Core会在不同的阶段调用该回调函数，用于该governor的启动、停止、初始化、退出动作
int (*governor) (struct cpufreq_policy *policy,
unsigned int event);
ssize_t (*show_setspeed) (struct cpufreq_policy *policy,
char *buf);
int (*store_setspeed) (struct cpufreq_policy *policy,
unsigned int freq);
unsigned int max_transition_latency; /* HW must be able to switch to
next freq faster than this value in nano secs or we
will fallback to performance governor */
//所有注册的governor都会利用该字段链接在一个全局链表中，以供系统查询和使用
struct list_head governor_list;
struct module *owner;
};driver
struct cpufreq_driver {
char name[CPUFREQ_NAME_LEN];
u8 flags;
void *driver_data;
/* needed by all drivers */
int (*init)(struct cpufreq_policy *policy);
int (*verify)(struct cpufreq_policy *policy);//检查policy的参数是否被支持
// 定义下面两个中的一个
/* define one out of two */
//如果不支持通过governor选择合适的运行频率，则实现setpolicy回调函数，
//这样系统只能支持CPUFREQ_POLICY_POWERSAVE和CPUFREQ_POLICY_PERFORMANCE这两种工作策略
int (*setpolicy)(struct cpufreq_policy *policy);
/*
* On failure, should always restore frequency to policy->restore_freq
* (i.e. old freq).
*/
//实现target回调函数，通过target回调设定governor所需要的频率
//target或者target_index设定目标频率
int (*target)(struct cpufreq_policy *policy,
unsigned int target_freq,
unsigned int relation); /* Deprecated */
int (*target_index)(struct cpufreq_policy *policy,
unsigned int index);
/*
* Only for drivers with target_index() and CPUFREQ_ASYNC_NOTIFICATION
* unset.
*
* get_intermediate should return a stable intermediate frequency
* platform wants to switch to and target_intermediate() should set CPU
* to to that frequency, before jumping to the frequency corresponding
* to 'index'. Core will take care of sending notifications and driver
* doesn't have to handle them in target_intermediate() or
* target_index().
*
* Drivers can return '0' from get_intermediate() in case they don't
* wish to switch to intermediate frequency for some target frequency.
* In that case core will directly call ->target_index().
*/
unsigned int (*get_intermediate)(struct cpufreq_policy *policy,
unsigned int index);
int (*target_intermediate)(struct cpufreq_policy *policy,
unsigned int index);
/* should be defined, if possible */
// 从硬件获取当前freq
unsigned int (*get)(unsigned int cpu);
/* optional */
int (*bios_limit)(int cpu, unsigned int *limit);
// 与init对应
int (*exit)(struct cpufreq_policy *policy);
void (*stop_cpu)(struct cpufreq_policy *policy);
// 针对boot cpu, 因为其他cpu已经在suspend前offline了
int (*suspend)(struct cpufreq_policy *policy);
int (*resume)(struct cpufreq_policy *policy);
/* Will be called after the driver is fully initialized */
void (*ready)(struct cpufreq_policy *policy);
struct freq_attr **attr;
/* platform specific boost support code */
bool boost_supported;
bool boost_enabled;
int (*set_boost)(int state);
};governor
struct cpufreq_governor {
char name[CPUFREQ_NAME_LEN];
int initialized;
//指向一个回调函数，CPUFreq Core会在不同的阶段调用该回调函数，用于该governor的启动、停止、初始化、退出动作
int (*governor) (struct cpufreq_policy *policy,
unsigned int event);
ssize_t (*show_setspeed) (struct cpufreq_policy *policy,
char *buf);
int (*store_setspeed) (struct cpufreq_policy *policy,
unsigned int freq);
unsigned int max_transition_latency; /* HW must be able to switch to
next freq faster than this value in nano secs or we
will fallback to performance governor */
//所有注册的governor都会利用该字段链接在一个全局链表中，以供系统查询和使用
struct list_head governor_list;
struct module *owner;
};