Linux Cpufreq框架

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cpufreq动态调频

cpufreq概述

Linux Kernel主要通过三类机制来实现SMP（Symmetric Multiprocessing，对称多核）系统CPU core的电源管理：

  • cpu hotplug: 根据应用场景来up/down CPU
  • cpuidle framework: 当cpu上没有可执行任务时，就会进入空闲状态
  • cpufreq framework: 根据使用场景和系统负荷来调整CPU的电压和频率

cpufreq framework的核心功能，是通过调整CPU core的电压或频率，兼顾系统的性能和功耗。在不需要高性能时，降低电压或频率，以降低功耗；在需要高性能时，提高电压或频率，以提高性能。

cpufreq framework中的几个重要概念：

  1. policy（策略）：同一个power domain CPU动态调频策略，包含了当前使用的governor和cpufreq driver
  2. governor（调节器）：决定如何计算合适的频率或电压
  3. cpufreq driver（调频驱动）：实现真正的调频执行工作（与平台相关）

除此之外，cpufreq还包含cpufreq stats, cpufreq qos, cpufreq notifier等辅助模块，其主要功能如下：

  1. cpufreq stats：用于搜集cpufreq的一些统计数据，如CPU在每个频点下的运行时间，总的频率切换次数等
  2. cpufreq qos：用于cpufreq频率限制值发生改变时，向cpufreq模块发送一个通知，将频率限制值调整到新的值
  3. cpufreq notifer：对CPU频率切换或policy对应governor发生改变感兴趣的模块，可以向cpufreq注册一个通知，当以上事件发生时，cpufreq将会向其发送相关通知

常用的governor类型

  1. Performance：总是将CPU置于最高性能的状态，即硬件所支持的最高频率、电压
  2. Powersaving：总是将CPU置于最节能的状态，即硬件所支持的最低频率、电压
  3. Ondemand：设置CPU负载的阈值T，当负载低于T时，调节至一个刚好能够满足当前负载需求的最低频/最低压；当负载高于T时，立即提升到最高性能状态
  4. Conservative：跟Ondemand策略类似，设置CPU负载的阈值T，当负载低于T时，调节至一个刚好能够满足当前负载需求的最低频/最低压；但当负载高于T时，不是立即设置为最高性能状态，而是逐级升高主频/电压
  5. Userspace：将控制接口通过sysfs开放给用户，由用户进行自定义策略
  6. Schedutil：这是从Linux-4.7版本开始才引入的策略，其原理是根据调度器所提供的CPU利用率信息进行电压/频率调节，EAS使用schedutil进行调频

sysfs用户层接口，目录位于/sys/devices/system/cpu/cpufreq/policy

名称 说明
cpuinfo_max_freq 硬件所支持的最高频率
cpuinfo_min_freq 硬件所支持的最低频率
affected_cpus 该policy影响到哪些cpu（没显示offline状态的cpu）
related_cpus 该policy影响到的所有cpu，包括offline状态的cpu
scaling_max_freq 该policy支持调整的最高频率
scaling_min_freq 该policy支持调整的最低频率
scaling_cur_freq policy当前设置的频率
scaling_available_governors 当前系统支持的governor
scaling_available_frequencies 支持的调频频率
scaling_driver 当前使用的调频驱动
scaling_governor 当前使用的governor
scaling_setspeed 在userspace模式下才能使用，手动设置频率

cpufreq软件架构


cpufreq core（可以理解为对policy的操作）：把一些公共的逻辑和接口代码抽象出来

  • cpufreq作为所有cpu设备的一个功能，注册到了cpu_subsys总线上
  • 对上以sysfs的形式向用户空间提供统一的接口，以notifier的形式向其他driver提供频率变化的通知
  • 对下提供CPU频率和电压控制的驱动框架，方便底层driver的开发，同时提供governor框架，用于实现不同的频率调整机制
  • 内部封装各种逻辑，主要围绕struct cpufreq_policy struct cpufreq_driver struct cpufreq_governor三个数据结构进行

kernel使用struct cpufreq_policy用来抽象cpufreq，它代表了一个CPU簇的cpufreq的属性

cpufreq_policy结构体

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struct cpufreq_cpuinfo {
	unsigned int		max_freq;			// cpu最大频率
	unsigned int		min_freq;			// cpu最小频率

	/* in 10^(-9) s = nanoseconds */
	unsigned int		transition_latency;	// cpu频率转换时间 单位：ns
};

struct cpufreq_policy {
	/* CPUs sharing clock, require sw coordination */
	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 */
	unsigned int		cpu;    /* cpu managing this policy, must be online */

	struct clk		*clk;
	struct cpufreq_cpuinfo	cpuinfo;/* see above */

	unsigned int		min;    /* in kHz */
	unsigned int		max;    /* in kHz */
	unsigned int		cur;    /* in kHz, only needed if cpufreq
					 * governors are used */

	struct cpufreq_governor	*governor; /* see below */
	void			*governor_data;
	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 */

	struct cpufreq_user_policy user_policy;
	struct cpufreq_frequency_table	*freq_table;
	enum cpufreq_table_sorting freq_table_sorted;

	struct list_head        policy_list;
	struct kobject		kobj;
	struct completion	kobj_unregister;

	/*
	 * 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		transition_delay_us;

	/*
	 * Remote DVFS flag (Not added to the driver structure as we don't want
	 * to access another structure from scheduler hotpath).
	 *
	 * Should be set if CPUs can do DVFS on behalf of other CPUs from
	 * different cpufreq policies.
	 */
	bool			dvfs_possible_from_any_cpu;

	 /* Cached frequency lookup from cpufreq_driver_resolve_freq. */
	unsigned int cached_target_freq;
	int cached_resolved_idx;

	/* cpufreq-stats */
	struct cpufreq_stats	*stats;

	/* For cpufreq driver's internal use */
	void			*driver_data;

	...
};

driver/cpufreq/cpufreq.c中定义了一个全局的percpu变量

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static DEFINE_PER_CPU(struct cpufreq_policy *, cpufreq_cpu_data);

这里对应E2000 sysfs中3个policy文件夹，两个小核使用1个policy，另外两个大核分别对应1个policy

cpufreq初始化

内核配置

在kconfig中(CPU Power Management -> CPU Frequency scaling)可以对cpufreq进行配置，可以配置支持的governor及系统默认的governor，以及cpufreq调频driver，例如Phytium E2000 5.10内核的配置如下，默认使用schedutil governor，根据调度器所提供的CPU利用率信息进行电压/频率调节，EAS能源感知依赖该governor工作：

OPP表初始化

OPP表的定义：域中每个设备支持的电压和频率的离散元组的集合称为Operating Performance Points（OPP）,内核设备树opp文档Documentation/devicetree/bindings/opp/opp.txt

假设一个CPU支持如下的电压和频率关系：
{300MHz at minimum voltage of 1V}
{800MHz at minimum voltage of 1.2V}
{1GHz at minimum voltage of 1.3V}
用OPP表示就可以用{Hz, uV}方式表示如下:
{300000000, 1000000}
{800000000, 1200000}
{1000000000, 1300000}

Linux内核使用opp layer库来管理opp table，具体的结构如下：

Linux内核使用struct dev_pm_opp结构表示设备的一OPP

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// drivers/opp/opp.h
struct dev_pm_opp {
	struct list_head node;
	struct kref kref;

	bool available;
	bool dynamic;
	bool turbo;
	bool suspend;
	unsigned int pstate;
	unsigned long rate;
	unsigned int level;

	struct dev_pm_opp_supply *supplies;
	struct dev_pm_opp_icc_bw *bandwidth;

	unsigned long clock_latency_ns;

	struct dev_pm_opp **required_opps;
	struct opp_table *opp_table;

	struct device_node *np;

#ifdef CONFIG_DEBUG_FS
	struct dentry *dentry;
#endif
};

Linux内核opp layer库的结构如下

这里初始化的就是各个性能域（即不同cluster）的OPP表，在E2000平台中是通过SCMI的Performace domain management protocol协议获取PERFORMANCE_DESCRIBE_LEVELS这个参数表，具体的协议实现源码在drivers/firmware/arm_scmi/perf.c里面，perf.c实现了SCMI的Performance domain managment protocol，scmi cpufreq_drvier也是通过perf_ops函数集进行调频

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// include/linux/scmi_protocol.h
// 抽象描述scmi协议的结构体，相应的ops操作集对应scmi的一个协议
struct scmi_handle {
	struct device *dev;
	struct scmi_revision_info *version;
	const struct scmi_perf_ops *perf_ops;
	const struct scmi_clk_ops *clk_ops;
	const struct scmi_power_ops *power_ops;
	const struct scmi_sensor_ops *sensor_ops;
	const struct scmi_reset_ops *reset_ops;
	const struct scmi_notify_ops *notify_ops;
	/* for protocol internal use */
	// perf_priv存放括performance domain数据，包含opp表等
	void *perf_priv;
	void *clk_priv;
	void *power_priv;
	void *sensor_priv;
	void *reset_priv;
	void *notify_priv;
	void *system_priv;
};

// include/linux/scmi_protocol.h
/**
 * struct scmi_perf_ops - represents the various operations provided
 *	by SCMI Performance Protocol
 *
 * @limits_set: sets limits on the performance level of a domain
 * @limits_get: gets limits on the performance level of a domain
 * @level_set: sets the performance level of a domain
 * @level_get: gets the performance level of a domain
 * @device_domain_id: gets the scmi domain id for a given device
 * @transition_latency_get: gets the DVFS transition latency for a given device
 * @device_opps_add: adds all the OPPs for a given device
 * @freq_set: sets the frequency for a given device using sustained frequency
 *	to sustained performance level mapping
 * @freq_get: gets the frequency for a given device using sustained frequency
 *	to sustained performance level mapping
 * @est_power_get: gets the estimated power cost for a given performance domain
 *	at a given frequency
 */
struct scmi_perf_ops {
	int (*limits_set)(const struct scmi_handle *handle, u32 domain,
			  u32 max_perf, u32 min_perf);
	int (*limits_get)(const struct scmi_handle *handle, u32 domain,
			  u32 *max_perf, u32 *min_perf);
	int (*level_set)(const struct scmi_handle *handle, u32 domain,
			 u32 level, bool poll);
	int (*level_get)(const struct scmi_handle *handle, u32 domain,
			 u32 *level, bool poll);
	int (*device_domain_id)(struct device *dev);
	int (*transition_latency_get)(const struct scmi_handle *handle,
				      struct device *dev);
	int (*device_opps_add)(const struct scmi_handle *handle,
			       struct device *dev);
	int (*freq_set)(const struct scmi_handle *handle, u32 domain,
			unsigned long rate, bool poll);
	int (*freq_get)(const struct scmi_handle *handle, u32 domain,
			unsigned long *rate, bool poll);
	int (*est_power_get)(const struct scmi_handle *handle, u32 domain,
			     unsigned long *rate, unsigned long *power);
	bool (*fast_switch_possible)(const struct scmi_handle *handle,
				     struct device *dev);
};

// scmi performance domain management protocol(性能域管理相关协议 0x13), messageid: 0x03
// scmi opp结构体定义
struct scmi_opp {
	u32 perf;		// 性能级别，单位KHz
	u32 power;		// 当前性能级别的功耗
	u32 trans_latency_us;	// 切换延时
};

// drivers/firmware/arm_scmi/perf.c
// scmi performance domain management protocol(性能域管理相关协议 0x13)对应操作函数集
// scmi cpufreq_driver 主要利用这个函数集进行调频相关操作
// 对应Performace domain management protocol各个message_id
static const struct scmi_perf_ops perf_ops = {
	.limits_set = scmi_perf_limits_set,
	.limits_get = scmi_perf_limits_get,
	.level_set = scmi_perf_level_set,
	.level_get = scmi_perf_level_get,
	.device_domain_id = scmi_dev_domain_id,
	.transition_latency_get = scmi_dvfs_transition_latency_get,
	.device_opps_add = scmi_dvfs_device_opps_add,
	.freq_set = scmi_dvfs_freq_set,
	.freq_get = scmi_dvfs_freq_get,
	.est_power_get = scmi_dvfs_est_power_get,
	.fast_switch_possible = scmi_fast_switch_possible,
};

// 在这个宏进行SCMI performance domain management protocol协议的初始化
DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(SCMI_PROTOCOL_PERF, perf)

// drivers/firmware/arm_scmi/common.h
#define DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(id, name) \
int __init scmi_##name##_register(void) \
{ \
	return scmi_protocol_register((id), &scmi_##name##_protocol_init); \
} \
\
void __exit scmi_##name##_unregister(void) \
{ \
	scmi_protocol_unregister((id)); \
}
// 展开该宏
int __init scmi_perf_register(void)
{
	return scmi_protocol_register(SCMI_PROTOCOL_PER, &scmi_perf_protocol_init);
}

// 初始化过程中调用了scmi_perf_protocol_init();
static int scmi_perf_protocol_init(struct scmi_handle *handle)
{
	int domain;
	u32 version;
	struct scmi_perf_info *pinfo;

	// 获取当前perf domain management协议版本
	scmi_version_get(handle, SCMI_PROTOCOL_PERF, &version);

	dev_dbg(handle->dev, "Performance Version %d.%d\n",
		PROTOCOL_REV_MAJOR(version), PROTOCOL_REV_MINOR(version));

	pinfo = devm_kzalloc(handle->dev, sizeof(*pinfo), GFP_KERNEL);
	if (!pinfo)
		return -ENOMEM;
	// 通过PROTOCOL_ATTRIBUTES(0x01)这个命令获取domain id个数
	// 还有share memory的地址和长度
	scmi_perf_attributes_get(handle, pinfo);

	// 分配perf_dom_info结构体内存，这里面的opp成员会存放OPP表
	// 对于E2000Q这里会分配3个大小的dom_info
	pinfo->dom_info = devm_kcalloc(handle->dev, pinfo->num_domains,
				       sizeof(*pinfo->dom_info), GFP_KERNEL);
	if (!pinfo->dom_info) 
		return -ENOMEM;

	// 遍历每个performance_domain，获取performance domain的属性和performance level参数
	for (domain = 0; domain < pinfo->num_domains; domain++) {
		struct perf_dom_info *dom = pinfo->dom_info + domain;

		// 获取performance domain属性
		scmi_perf_domain_attributes_get(handle, domain, dom);
		// 获取performance level参数即opp表
		// 填充perf_dom_info内的opp结构体
		scmi_perf_describe_levels_get(handle, domain, dom);

		if (dom->perf_fastchannels)
			scmi_perf_domain_init_fc(handle, domain, &dom->fc_info);
	}

	scmi_register_protocol_events(handle,
				      SCMI_PROTOCOL_PERF, SCMI_PROTO_QUEUE_SZ,
				      &perf_event_ops, perf_events,
				      ARRAY_SIZE(perf_events),
				      pinfo->num_domains);

	pinfo->version = version;
	handle->perf_ops = &perf_ops;
	// perf_priv保存performance domain信息，后续会用到perf_priv
	handle->perf_priv = pinfo;

	return 0;
}

在初始化阶段，scmi_perf_protocol_init只会将固件里面的perf domains信息保存到handle->perf_priv里面，此时还并没有将opp表注册到cpu设备上

接下来在scmi调频驱动初始化的过程中，会调用scmi的device_opps_add()接口初始化，即调用scmi_dvfs_device_opps_add()，在这个里面才会生成cpu的opp_table

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static int scmi_dvfs_device_opps_add(const struct scmi_handle *handle,
				     struct device *dev)
{
	int idx, ret, domain;
	unsigned long freq;
	struct scmi_opp *opp;
	struct perf_dom_info *dom;
	// 获取pref_priv地址，在这里面取opp数据
	struct scmi_perf_info *pi = handle->perf_priv;
	// 这个domain是从设备树里面取到的，设备树cpu节点的clock属性会带一个domain编号
	domain = scmi_dev_domain_id(dev);
	if (domain < 0)
		return domain;
	// 取当前CPU的perf domain信息
	dom = pi->dom_info + domain;
	// struct perf_dom_info结构体里面一共16个opp表
	// 这里没对opp进行限制，可能有数组越界的问题
	for (opp = dom->opp, idx = 0; idx < dom->opp_count; idx++, opp++) {
		freq = opp->perf * dom->mult_factor;
		// 这里面第一次会为opp_table分配内存，这里只将频率加进opp table里了
		ret = dev_pm_opp_add(dev, freq, 0);
		if (ret) {
			dev_warn(dev, "failed to add opp %luHz\n", freq);

			while (idx-- > 0) {
				freq = (--opp)->perf * dom->mult_factor;
				dev_pm_opp_remove(dev, freq);
			}
			return ret;
		}
	}
	return 0;
}

详细看一下dev_pm_opp_add()的过程

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// drviers/opp/opp.h
// opp_table结构体的定义
struct opp_table {
	struct list_head node;

	struct blocking_notifier_head head;
	struct list_head dev_list;			// 共享该opp表的设备链表
	struct list_head opp_list;
	struct kref kref;
	struct mutex lock;

	struct device_node *np;
	unsigned long clock_latency_ns_max;

	/* For backward compatibility with v1 bindings */
	unsigned int voltage_tolerance_v1;

	unsigned int parsed_static_opps;
	enum opp_table_access shared_opp;
	struct dev_pm_opp *suspend_opp;

	struct mutex genpd_virt_dev_lock;
	struct device **genpd_virt_devs;
	struct opp_table **required_opp_tables;
	unsigned int required_opp_count;

	unsigned int *supported_hw;
	unsigned int supported_hw_count;
	const char *prop_name;
	struct clk *clk;
	struct regulator **regulators;
	int regulator_count;
	struct icc_path **paths;
	unsigned int path_count;
	bool enabled;
	bool genpd_performance_state;
	bool is_genpd;

	int (*set_opp)(struct dev_pm_set_opp_data *data);
	struct dev_pm_set_opp_data *set_opp_data;

#ifdef CONFIG_DEBUG_FS
	struct dentry *dentry;
	char dentry_name[NAME_MAX];
#endif
};

// drivers/opp/core.c
/*
 * The root of the list of all opp-tables. All opp_table structures branch off
 * from here, with each opp_table containing the list of opps it supports in
 * various states of availability.
 */
// opp_tables是opp_table链表的头节点
LIST_HEAD(opp_tables);

static struct opp_device *_find_opp_dev(const struct device *dev,
							struct opp_table *opp_table)
{
	struct opp_device *opp_dev;
	// 从opp_table的dev_list中的dev与当前dev进行对比
	list_for_each_entry(opp_dev, &opp_table->dev_list, node)
		if (opp_dev->dev == dev)
			return opp_dev;

	return NULL;
}

static struct opp_table *_find_opp_table_unlocked(struct device *dev)
{
	struct opp_table *opp_table;
	bool found;
	// 在opp_tables中进行遍历查找当前设备对应的opp_table
	list_for_each_entry(opp_table, &opp_tables, node) {
		mutex_lock(&opp_table->lock);
		found = !!_find_opp_dev(dev, opp_table);
		mutex_unlock(&opp_table->lock);

		if (found) {
			// opp_table的引用计数加一
			_get_opp_table_kref(opp_table);

			return opp_table;
		}
	}

	return ERR_PTR(-ENODEV);
}

static struct opp_table *_opp_get_opp_table(struct device *dev, int index)
{
	struct opp_table *opp_table;

	/* Hold our table modification lock here */
	mutex_lock(&opp_table_lock);

	// 第一次运行到这里的时候，应该是找不到opp_table的，需要进行创建
	opp_table = _find_opp_table_unlocked(dev);
	if (!IS_ERR(opp_table))
		goto unlock;

	opp_table = _managed_opp(dev, index);
	if (opp_table) {
		if (!_add_opp_dev_unlocked(dev, opp_table)) {
			dev_pm_opp_put_opp_table(opp_table);
			opp_table = ERR_PTR(-ENOMEM);
		}
		goto unlock;
	}
	// 对该设备创建opp表
	opp_table = _allocate_opp_table(dev, index);

unlock:
	mutex_unlock(&opp_table_lock);

	return opp_table;
}


struct opp_table *dev_pm_opp_get_opp_table(struct device *dev)
{
	return _opp_get_opp_table(dev, 0);
}

int dev_pm_opp_add(struct device *dev, unsigned long freq, unsigned long u_volt)
{
	struct opp_table *opp_table;
	int ret;

	opp_table = dev_pm_opp_get_opp_table(dev);
	if (IS_ERR(opp_table)) 
		return PTR_ERR(opp_table);
	
	opp_table->regulator_count = 1;
	
	ret = _opp_add_v1(opp_table, dev, freq, u_volt, true);
	if (ret)
		dev_pm_opp_put_opp_table(opp_table);
	
	return ret;
}

最终获取得到的OPP表如下

cpufreq初始化过程

cpufreq被注册cpu_subsys总线上

cpufreq的初始化从cpufreq_drvier注册开始，cpufreq_register_driver()函数为cpufreq驱动注册的入口，驱动程序通过调用该函数进行初始化，传入相关的struct cpufreq_driver，cpufreq_register_driver()会调用subsys_interface_register()最终执行回调函数cpufreq_add_dev，然后调用cpufreq_online()走初始化流程

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// cpufreq_drvier结构体
struct cpufreq_driver {
	char		name[CPUFREQ_NAME_LEN];
	u16		    flags;
	void		*driver_data;

	/* needed by all drivers */
	int		(*init)(struct cpufreq_policy *policy);
	int		(*verify)(struct cpufreq_policy_data *policy);
	// 调频接口
	int		(*target_index)(struct cpufreq_policy *policy,
					unsigned int index);
	unsigned int	(*fast_switch)(struct cpufreq_policy *policy,
				       unsigned int target_freq);

	/* should be defined, if possible */
	// 获取频率接口
	unsigned int	(*get)(unsigned int cpu);

	/* Called to update policy limits on firmware notifications. */
	void		(*update_limits)(unsigned int cpu);

	int		(*online)(struct cpufreq_policy *policy);
	int		(*offline)(struct cpufreq_policy *policy);
	int		(*exit)(struct cpufreq_policy *policy);

	struct freq_attr **attr;
};

// driver/base/cpu.c
// cpu subsys总线，cpufreq就是以subsys_interface挂在该总线下
struct bus_type cpu_subsys = {
	.name = "cpu",
	.dev_name = "cpu",
	.match = cpu_subsys_match,
	.online = cpu_subsys_online,
	.offline = cpu_subsys_offline,
};

// driver/cpufreq/cpufreq.c
// 指向当前使用的cpufreq_driver
static struct cpufreq_driver *cpufreq_driver;

// cpufreq subsys接口，用来挂到CPU subsys总线上
static struct subsys_interface cpufreq_interface = {
	.name		= "cpufreq",
	.subsys		= &cpu_subsys,
	.add_dev	= cpufreq_add_dev,
	.remove_dev	= cpufreq_remove_dev,
};

// scmi cpufreq_driver结构体定义
static struct cpufreq_driver scmi_cpufreq_driver = {
	.name	= "scmi",
	.flags	= CPUFREQ_STICKY | CPUFREQ_HAVE_GOVERNOR_PER_POLICY |
		  CPUFREQ_NEED_INITIAL_FREQ_CHECK,
	.verify	= cpufreq_generic_frequency_table_verify,
	.attr	= cpufreq_generic_attr,
	.target_index	= scmi_cpufreq_set_target,
	.fast_switch	= scmi_cpufreq_fast_switch,
	.get	= scmi_cpufreq_get_rate,
	.init	= scmi_cpufreq_init,
	.exit	= scmi_cpufreq_exit,
	.ready	= scmi_cpufreq_ready,
};

// 为每个cluster定义一个cpufreq_policy结构体，对每个cluster上的CPU进行调频管理
// 其中又分别进行cpufreq_driver的初始化和governor的初始化
static DEFINE_PER_CPU(struct cpufreq_policy *, cpufreq_cpu_data);

// 指向当前注册的cpufreq driver
static struct cpufreq_driver *cpufreq_driver;

// cpufreq驱动框架初始化过程，整个过程都围绕着policy这个结构体进行，逐步进行初始化
cpufreq_register_driver(&scmi_cpufreq_driver);
	subsys_interface_register(&cpufreq_interface);
		cpufreq_add_dev(dev, sif);
			cpufreq_online(cpu);
				// 初步初始化policy
				// cpumask初始化
				// policy->kobj kobject初始化
				// policy->constraints 频率限制初始化
				// 注册频率限制通知接口，频率最大最小值变化时会调用接口
				policy = cpufreq_policy_alloc(cpu);
				// 调用cpufreq_drvier init接口，完善policy结构体
				// 将opp表添加到对应的device，通过dev_pm_opp_add接口
				// 生成频率表 freq_table
				cpufreq_driver->init(policy) -> scmi_cpufreq_init(policy)
				cpufreq_table_validate_and_sort(policy);
				// 创建/sys/device/system/cpu/cpux目录下的cpufreq符号链接
				add_cpu_dev_symlink();
				freq_qos_and_request();
				blocking_notifier_call_chain();
				// CPU进行频率调整，使当前运行频率在频率表中
				// 初始化的时候会进行一次调整
				__cpufreq_driver_target();
				// 创建sys节点，/sys/device/system/cpu/cpufreq/policyx目录下的一些可选属性
				cpufreq_add_dev_interface(policy);
				cpufreq_stats_create_table(policy);
				list_add(&policy->polic_list, &cpufreq_policy_list);
				// 使用默认governor初始化policy
				cpufreq_init_policy();

来看一下subsys_interface_register()

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// drivers/base/bus.c
int subsys_interface_register(struct subsystem_interface *sif)
{
	struct bus_type *subsys;
	struct subsys_dev_iter iter;
	struct device *dev;

	if (!sif || !sif->subsys)
		return -ENODEV;

	subsys = bus_get(sif->subsys);
	if (!subsys)
		return -EINVAL;

	mutex_lock(&subsys->p->mutex);
	// 将cpufreq_interface添加到cpu_subsys总线的interfaces上
	// interfaces是一个list_head链表
	list_add_tail(&sif->node, &subsys->p->interfaces);

	// 遍历cpu_subsys总线
	// subsys_dev_iter是对klist 迭代器的一个封装
	// 这里遍历的对象是struct device私有数据的knode_bus
	// knode_bus节点是挂载到klist_device这个链表上
	if (sif->add_dev) {
		subsys_dev_iter_init(&iter, subsys, NULL, NULL);
		// 从knode_bus取得device指针
		while ((dev = subsys_dev_iter_next(&iter)))
			sif->add_dev(dev, sif);
		subsys_dev_iter_exit(&iter);
	}
	mutex_unlock(&subsys->p->mutex);

	return 0;
}

再来看看cpufreq_online()

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static int cpufreq_online(unsigned int cpu)
{
	struct cpufreq_policy *policy;
	bool new_policy;
	unsigned long flags;
	unsigned int j;
	int ret;

	pr_debug("%s: bringing CPU%u online\n", __func__, cpu);

	/* Check if this CPU already has a policy to manage it */
	// cpufreq_cpu_data是类型为policy指针的precpu变量
	// 这是是取得policy指针
	policy = per_cpu(cpufreq_cpu_data, cpu);
	if (policy) {
		// 假如该cpu不在该policy的related_cpus里面则是有问题的
		WARN_ON(!cpumask_test_cpu(cpu, policy->related_cpus));
		// 判断当前policy还有没有online CPU
		if (!policy_is_inactive(policy))
			// 将当前cpu加入到policy->cpu online CPU里面
			return cpufreq_add_policy_cpu(policy, cpu);

		/* This is the only online CPU for the policy.  Start over. */
		new_policy = false;
		down_write(&policy->rwsem);
		policy->cpu = cpu;
		policy->governor = NULL;
		up_write(&policy->rwsem);
	} else {
		// 第一次开机的时候需要分配policy内存
		new_policy = true;
		policy = cpufreq_policy_alloc(cpu);
		if (!policy)
			return -ENOMEM;
	}

	// scmi调频驱动没有实现online接口
	if (!new_policy && cpufreq_driver->online) {
		ret = cpufreq_driver->online(policy);
		if (ret) {
			pr_debug("%s: %d: initialization failed\n", __func__,
				 __LINE__);
			goto out_exit_policy;
		}

		/* Recover policy->cpus using related_cpus */
		cpumask_copy(policy->cpus, policy->related_cpus);
	} else {
		cpumask_copy(policy->cpus, cpumask_of(cpu));

		/*
		 * Call driver. From then on the cpufreq must be able
		 * to accept all calls to ->verify and ->setpolicy for this CPU.
		 */
		// cpufreq_driver是在cpufreq_register_driver()中进行赋值的
		// 调频驱动初始化
		ret = cpufreq_driver->init(policy);
		if (ret) {
			pr_debug("%s: %d: initialization failed\n", __func__,
				 __LINE__);
			goto out_free_policy;
		}

		ret = cpufreq_table_validate_and_sort(policy);
		if (ret)
			goto out_exit_policy;

		/* related_cpus should at least include policy->cpus. */
		cpumask_copy(policy->related_cpus, policy->cpus);
	}

	down_write(&policy->rwsem);
	/*
	 * affected cpus must always be the one, which are online. We aren't
	 * managing offline cpus here.
	 */
	cpumask_and(policy->cpus, policy->cpus, cpu_online_mask);

	if (new_policy) {
		for_each_cpu(j, policy->related_cpus) {
			per_cpu(cpufreq_cpu_data, j) = policy;
			add_cpu_dev_symlink(policy, j);
		}

		policy->min_freq_req = kzalloc(2 * sizeof(*policy->min_freq_req),
					       GFP_KERNEL);
		if (!policy->min_freq_req)
			goto out_destroy_policy;

		ret = freq_qos_add_request(&policy->constraints,
					   policy->min_freq_req, FREQ_QOS_MIN,
					   policy->min);
		if (ret < 0) {
			/*
			 * So we don't call freq_qos_remove_request() for an
			 * uninitialized request.
			 */
			kfree(policy->min_freq_req);
			policy->min_freq_req = NULL;
			goto out_destroy_policy;
		}

		/*
		 * This must be initialized right here to avoid calling
		 * freq_qos_remove_request() on uninitialized request in case
		 * of errors.
		 */
		policy->max_freq_req = policy->min_freq_req + 1;

		ret = freq_qos_add_request(&policy->constraints,
					   policy->max_freq_req, FREQ_QOS_MAX,
					   policy->max);
		if (ret < 0) {
			policy->max_freq_req = NULL;
			goto out_destroy_policy;
		}

		blocking_notifier_call_chain(&cpufreq_policy_notifier_list,
				CPUFREQ_CREATE_POLICY, policy);
	}

	if (cpufreq_driver->get && has_target()) {
		policy->cur = cpufreq_driver->get(policy->cpu);
		if (!policy->cur) {
			pr_err("%s: ->get() failed\n", __func__);
			goto out_destroy_policy;
		}
	}

	/*
	 * Sometimes boot loaders set CPU frequency to a value outside of
	 * frequency table present with cpufreq core. In such cases CPU might be
	 * unstable if it has to run on that frequency for long duration of time
	 * and so its better to set it to a frequency which is specified in
	 * freq-table. This also makes cpufreq stats inconsistent as
	 * cpufreq-stats would fail to register because current frequency of CPU
	 * isn't found in freq-table.
	 *
	 * Because we don't want this change to effect boot process badly, we go
	 * for the next freq which is >= policy->cur ('cur' must be set by now,
	 * otherwise we will end up setting freq to lowest of the table as 'cur'
	 * is initialized to zero).
	 *
	 * We are passing target-freq as "policy->cur - 1" otherwise
	 * __cpufreq_driver_target() would simply fail, as policy->cur will be
	 * equal to target-freq.
	 */
	if ((cpufreq_driver->flags & CPUFREQ_NEED_INITIAL_FREQ_CHECK)
	    && has_target()) {
		unsigned int old_freq = policy->cur;

		/* Are we running at unknown frequency ? */
		ret = cpufreq_frequency_table_get_index(policy, old_freq);
		if (ret == -EINVAL) {
			ret = __cpufreq_driver_target(policy, old_freq - 1,
						      CPUFREQ_RELATION_L);

			/*
			 * Reaching here after boot in a few seconds may not
			 * mean that system will remain stable at "unknown"
			 * frequency for longer duration. Hence, a BUG_ON().
			 */
			BUG_ON(ret);
			pr_info("%s: CPU%d: Running at unlisted initial frequency: %u KHz, changing to: %u KHz\n",
				__func__, policy->cpu, old_freq, policy->cur);
		}
	}

	if (new_policy) {
		ret = cpufreq_add_dev_interface(policy);
		if (ret)
			goto out_destroy_policy;

		cpufreq_stats_create_table(policy);

		write_lock_irqsave(&cpufreq_driver_lock, flags);
		list_add(&policy->policy_list, &cpufreq_policy_list);
		write_unlock_irqrestore(&cpufreq_driver_lock, flags);
	}

	ret = cpufreq_init_policy(policy);
	if (ret) {
		pr_err("%s: Failed to initialize policy for cpu: %d (%d)\n",
		       __func__, cpu, ret);
		goto out_destroy_policy;
	}

	up_write(&policy->rwsem);

	kobject_uevent(&policy->kobj, KOBJ_ADD);

	/* Callback for handling stuff after policy is ready */
	if (cpufreq_driver->ready)
		cpufreq_driver->ready(policy);

	if (cpufreq_thermal_control_enabled(cpufreq_driver))
		policy->cdev = of_cpufreq_cooling_register(policy);

	pr_debug("initialization complete\n");

	return 0;

out_destroy_policy:
	for_each_cpu(j, policy->real_cpus)
		remove_cpu_dev_symlink(policy, get_cpu_device(j));

	up_write(&policy->rwsem);

out_exit_policy:
	if (cpufreq_driver->exit)
		cpufreq_driver->exit(policy);

out_free_policy:
	cpufreq_policy_free(policy);
	return ret;
}

cpufreq drviver初始化

在cpufreq_online()中调用全局变量cpufreq_driver->init(policy)进行调频驱动的初始化，下面是scmi调频驱动的初始化过程

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static int scmi_cpufreq_init(struct cpufreq_policy *policy)
{
	int ret, nr_opp;
	unsigned int latency;
	struct device *cpu_dev;
	struct scmi_data *priv;
	struct cpufreq_frequency_table *freq_table;
	struct em_data_callback em_cb = EM_DATA_CB(scmi_get_cpu_power);

	// 获取CPU device结构体即对应percpu变量cpu_sys_devices
	cpu_dev = get_cpu_device(policy->cpu);
	if (!cpu_dev) {
		pr_err("failed to get cpu%d device\n", policy->cpu);
		return -ENODEV;
	}

	// 调用scmi_dvfs_device_opps_add()生成opp表
	ret = handle->perf_ops->device_opps_add(handle, cpu_dev);
	if (ret) {
		dev_warn(cpu_dev, "failed to add opps to the device\n");
		return ret;
	}
	// 遍历可用的cpu，对比cpu_dev的domain_id，若是相同的话加入到policy->cpus里面
	ret = scmi_get_sharing_cpus(cpu_dev, policy->cpus);
	if (ret) {
		dev_warn(cpu_dev, "failed to get sharing cpumask\n");
		return ret;
	}
	// 将opp表添加到sharing cpus里面
	ret = dev_pm_opp_set_sharing_cpus(cpu_dev, policy->cpus);
	if (ret) {
		dev_err(cpu_dev, "%s: failed to mark OPPs as shared: %d\n",
			__func__, ret);
		return ret;
	}

	nr_opp = dev_pm_opp_get_opp_count(cpu_dev);
	if (nr_opp <= 0) {
		dev_dbg(cpu_dev, "OPP table is not ready, deferring probe\n");
		ret = -EPROBE_DEFER;
		goto out_free_opp;
	}

	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
	if (!priv) {
		ret = -ENOMEM;
		goto out_free_opp;
	}
	// cpufreq
	ret = dev_pm_opp_init_cpufreq_table(cpu_dev, &freq_table);
	if (ret) {
		dev_err(cpu_dev, "failed to init cpufreq table: %d\n", ret);
		goto out_free_priv;
	}

	priv->cpu_dev = cpu_dev;
	priv->domain_id = handle->perf_ops->device_domain_id(cpu_dev);
	// driver_data保存了调频驱动的一些数据，这里只有cpu编号和domain id号
	policy->driver_data = priv;
	policy->freq_table = freq_table;

	/* SCMI allows DVFS request for any domain from any CPU */
	policy->dvfs_possible_from_any_cpu = true;

	latency = handle->perf_ops->transition_latency_get(handle, cpu_dev);
	if (!latency)
		latency = CPUFREQ_ETERNAL;

	policy->cpuinfo.transition_latency = latency;

	policy->fast_switch_possible =
		handle->perf_ops->fast_switch_possible(handle, cpu_dev);

	em_dev_register_perf_domain(cpu_dev, nr_opp, &em_cb, policy->cpus);

	return 0;

out_free_priv:
	kfree(priv);
out_free_opp:
	dev_pm_opp_remove_all_dynamic(cpu_dev);

	return ret;
}

频率表初始化过程

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struct cpufreq_frequency_table {
	unsigned int flags;
	unsigned int driver_data;
	unsigned int frequency;		/* KHz */
};

// drivers/opp/cpu.c
int dev_pm_opp_init_cpufreq_table(struct device *dev,
				  struct cpufreq_frequency_table **table)
{
	struct dev_pm_opp *opp;
	struct cpufreq_frequency_table *freq_table = NULL;
	int i, max_opps, ret = 0;
	unsigned long rate;

	max_opps = dev_pm_opp_get_opp_count(dev);
	if (max_opps <= 0)
		return max_opps ? max_opps : -ENODATA;

	freq_table = kcalloc((max_opps + 1), sizeof(*freq_table), GFP_KERNEL);
	if (!freq_table)
		return -ENOMEM;

	for (i = 0, rate = 0; i < max_opps; i++, rate++) {
		/* find next rate */
		opp = dev_pm_opp_find_freq_ceil(dev, &rate);
		if (IS_ERR(opp)) {
			ret = PTR_ERR(opp);
			goto out;
		}
		freq_table[i].driver_data = i;
		freq_table[i].frequency = rate / 1000;

		/* Is Boost/turbo opp ? */
		if (dev_pm_opp_is_turbo(opp))
			freq_table[i].flags = CPUFREQ_BOOST_FREQ;

		dev_pm_opp_put(opp);
	}

	freq_table[i].driver_data = i;
	freq_table[i].frequency = CPUFREQ_TABLE_END;

	*table = &freq_table[0];

out:
	if (ret)
		kfree(freq_table);

	return ret;
}

governor初始化过程

cpufreq governor的初始化过程，在cpufreq_init_policy(policy)中进行，这里以ondemand为例进行分析

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// include/linux/cpufreq.h
// 内核governor描述结构体，形成链表
struct cpufreq_governor {
	char	name[CPUFREQ_NAME_LEN];
	int	(*init)(struct cpufreq_policy *policy);
	void	(*exit)(struct cpufreq_policy *policy);
	int	(*start)(struct cpufreq_policy *policy);
	void	(*stop)(struct cpufreq_policy *policy);
	void	(*limits)(struct cpufreq_policy *policy);
	ssize_t	(*show_setspeed)	(struct cpufreq_policy *policy,
					 char *buf);
	int	(*store_setspeed)	(struct cpufreq_policy *policy,
					 unsigned int freq);
	struct list_head	governor_list;
	struct module		*owner;
	u8			flags;
};

/* Common Governor data across policies */
// 抽象出的ondemand governor结构体
// drivers/cpufreq/cpufreq_governor.h
struct dbs_governor {
	struct cpufreq_governor gov;
	struct kobj_type kobj_type;
	/*
	 * Common data for platforms that don't set
	 * CPUFREQ_HAVE_GOVERNOR_PER_POLICY
	 */
	struct dbs_data *gdbs_data;

	unsigned int (*gov_dbs_update)(struct cpufreq_policy *policy);
	struct policy_dbs_info *(*alloc)(void);
	void (*free)(struct policy_dbs_info *policy_dbs);
	int (*init)(struct dbs_data *dbs_data);
	void (*exit)(struct dbs_data *dbs_data);
	void (*start)(struct cpufreq_policy *policy);
};

/* Governor demand based switching data (per-policy or global). */
// ondemand计算频率使用的相关参数，包括阈值 采样率等，默认阈值是负载的80%
// dbs(demand based switching)按需切换
struct dbs_data {
	struct gov_attr_set attr_set;
	void *tuners;
	unsigned int ignore_nice_load;
	unsigned int sampling_rate;
	unsigned int sampling_down_factor;
	unsigned int up_threshold;
	unsigned int io_is_busy;
};

/* Common to all CPUs of a policy */
// driver/cpufreq/cpufreq_governor.h
struct policy_dbs_info {
	struct cpufreq_policy *policy;
	/*
	 * Per policy mutex that serializes load evaluation from limit-change
	 * and work-handler.
	 */
	struct mutex update_mutex;

	u64 last_sample_time;
	s64 sample_delay_ns;
	atomic_t work_count;
	struct irq_work irq_work;
	struct work_struct work;
	/* dbs_data may be shared between multiple policy objects */
	struct dbs_data *dbs_data;
	struct list_head list;
	/* Multiplier for increasing sample delay temporarily. */
	unsigned int rate_mult;
	unsigned int idle_periods;	/* For conservative */
	/* Status indicators */
	bool is_shared;		/* This object is used by multiple CPUs */
	bool work_in_progress;	/* Work is being queued up or in progress */
};

// drivers/cpufreq/cpufreq_governor.h
// governor初始化宏
#define CPUFREQ_DBS_GOVERNOR_INITIALIZER(_name_)			\
	{								\
		.name = _name_,						\
		.flags = CPUFREQ_GOV_DYNAMIC_SWITCHING,			\
		.owner = THIS_MODULE,					\
		.init = cpufreq_dbs_governor_init,			\
		.exit = cpufreq_dbs_governor_exit,			\
		.start = cpufreq_dbs_governor_start,			\
		.stop = cpufreq_dbs_governor_stop,			\
		.limits = cpufreq_dbs_governor_limits,			\
	}

// ondemand governor定义
// driver/cpufreq/cpufreq_ondemand.c
static struct dbs_governor od_dbs_gov = {
	.gov = CPUFREQ_DBS_GOVERNOR_INITIALIZER("ondemand"),
	.kobj_type = { .default_attrs = od_attributes },
	.gov_dbs_update = od_dbs_update,
	.alloc = od_alloc,
	.free = od_free,
	.init = od_init,
	.exit = od_exit,
	.start = od_start,
};

// 初始化governor
// 该函数会在governor模块驱动的入口函数调用
// 只要编译该模块，就会注册到cpufreq framework中
#define CPU_FREQ_GOV_ONDEMAND	(od_dbs_gov.gov)
cpufreq_governor_init(CPU_FREQ_GOV_ONDEMAND);

#define cpufreq_governor_init(__governor)			\
static int __init __governor##_init(void)			\
{								\
	return cpufreq_register_governor(&__governor);	\
}								\
core_initcall(__governor##_init)

// 在cpufreq_online()中调用默认governor对policy进行完善，启动当前governor
cpufreq_init_policy(policy);
	gov = get_governor(default_governor);
	// 设置新的governor
	cpufreq_set_policy(policy, gov, pol);
		cpufreq_init_governor(policy);
			policy->governor->init();  -> cpufreq_dbs_governor_init(policy);
				gov->init(dbs_data); -> odinit(dbs_data);
		cpufreq_start_governor(policy);
			policy->governor->start(); -> cpufreq_dbs_governor_start(policy);
				// 设置governor回调函数， 以ondemand为例
				gov_set_update_util(policy_dbs, sampling_rate);
					cpufreq_add_update_util_hook(cpu, &cdbs->updata_util,
									dbs_update_util_handler);

启动governor中比较重要的是设置调频回调函数,该函数是真正调频时计算合适频率的函数

ondemand调节器

ondemand调节器也会根据当前的CPU负载来进行CPU频率计算，ondemand工作过程如下

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// include/linux/sched/cpufreq.h
// CPU利用率变化时会调用func重新计算频率
struct update_util_data {
    void (*func)(struct update_util_data *data, u64 time, unsigned int flags);
};

// drivers/cpufreq/cpufreq_governor.c
// 设置governor回调函数update_util_data->func = dbs_update_util_handler
cpufreq_dbs_governor_start()
    gov_set_update_util(policy_dbs, sampling_rate);
		cpufreq_add_update_util_hook(cpu, &cdbs->update_util,
                                    dbs_update_util_handler);

/**
 * cpufreq_update_util - Take a note about CPU utilization changes.
 * @rq: Runqueue to carry out the update for.
 * @flags: Update reason flags.
 *
 * This function is called by the scheduler on the CPU whose utilization is
 * being updated.
 *
 * It can only be called from RCU-sched read-side critical sections.
 *
 * The way cpufreq is currently arranged requires it to evaluate the CPU
 * performance state (frequency/voltage) on a regular basis to prevent it from
 * being stuck in a completely inadequate performance level for too long.
 * That is not guaranteed to happen if the updates are only triggered from CFS
 * and DL, though, because they may not be coming in if only RT tasks are
 * active all the time (or there are RT tasks only).
 *
 * As a workaround for that issue, this function is called periodically by the
 * RT sched class to trigger extra cpufreq updates to prevent it from stalling,
 * but that really is a band-aid.  Going forward it should be replaced with
 * solutions targeted more specifically at RT tasks.
 */
// kernel/sched/sched.h
// 当cpufreq_update_util()被调用时执行上面设置的回调函数update_util_data->func
// 为了考虑RT任务的影响，目前在RT调度中会周期性调用该函数，避免CPU频率更新不及时
static inline void cpufreq_update_util(struct rq *rq, unsigned int flags)
{
    struct update_util_data *data;
    data = rcu_dereference_sched(*per_cpu_ptr(&cpufreq_update_util_data,
                                cpu_of(rq)));
    if (data)
        data->func(data, rq_clock(rq), flags);
}

// drivers/cpufreq/cpufreq_governor.c
// data: 为了后续计算过程能够使用container_of取到cpu_dbs_info地址
// time: 运行队列更新的时间
// flags: 更新的原因标志
static void dbs_update_util_handler(struct update_util_data *data, u64 time,
				    unsigned int flags)
{
	struct cpu_dbs_info *cdbs = container_of(data, struct cpu_dbs_info, update_util);
	struct policy_dbs_info *policy_dbs = cdbs->policy_dbs;
	u64 delta_ns, lst;

    // 检查当前工作的CPU可否对该policy对应的CPU进行调频，E2000是支持的
	if (!cpufreq_this_cpu_can_update(policy_dbs->policy))
		return;

	/*
	 * The work may not be allowed to be queued up right now.
	 * Possible reasons:
	 * - Work has already been queued up or is in progress.
	 * - It is too early (too little time from the previous sample).
	 */
	if (policy_dbs->work_in_progress)
		return;

	/*
	 * If the reads below are reordered before the check above, the value
	 * of sample_delay_ns used in the computation may be stale.
	 */
    // 判断更新的时间间隔，假如小于smaple_delay_ns直接返回
	smp_rmb();
	lst = READ_ONCE(policy_dbs->last_sample_time);
	delta_ns = time - lst;
	if ((s64)delta_ns < policy_dbs->sample_delay_ns)
		return;

	/*
	 * If the policy is not shared, the irq_work may be queued up right away
	 * at this point.  Otherwise, we need to ensure that only one of the
	 * CPUs sharing the policy will do that.
	 */
    // 若policy是被多个CPU共享的，那么要判断一下是不是已经有CPU对其进行处理过了
	if (policy_dbs->is_shared) {
		if (!atomic_add_unless(&policy_dbs->work_count, 1, 1))
			return;

		/*
		 * If another CPU updated last_sample_time in the meantime, we
		 * shouldn't be here, so clear the work counter and bail out.
		 */
		if (unlikely(lst != READ_ONCE(policy_dbs->last_sample_time))) {
			atomic_set(&policy_dbs->work_count, 0);
			return;
		}
	}

    // 更新标志位
	policy_dbs->last_sample_time = time;
	policy_dbs->work_in_progress = true;
	irq_work_queue(&policy_dbs->irq_work);
}

// drivers/cpufreq/cpufreq_governor.c
// init_irq_work(&policy_dbs->irq_work, dbs_irq_work)
static void dbs_irq_work(struct irq_work *irq_work)
{
	struct policy_dbs_info *policy_dbs;

	policy_dbs = container_of(irq_work, struct policy_dbs_info, irq_work);
    // 调度policy_dbs->work执行
	schedule_work_on(smp_processor_id(), &policy_dbs->work);
}

// drivers/cpufreq/cpufreq_governor.c
// INIT_WORK(&policy_dbs->work, dbs_work_handler)
static void dbs_work_handler(struct work_struct *work)
{
	struct policy_dbs_info *policy_dbs;
	struct cpufreq_policy *policy;
	struct dbs_governor *gov;

	policy_dbs = container_of(work, struct policy_dbs_info, work);
	policy = policy_dbs->policy;
	gov = dbs_governor_of(policy);

	/*
	 * Make sure cpufreq_governor_limits() isn't evaluating load or the
	 * ondemand governor isn't updating the sampling rate in parallel.
	 */
    // 调用gov->gov_dbs_update()接口
	mutex_lock(&policy_dbs->update_mutex);
	gov_update_sample_delay(policy_dbs, gov->gov_dbs_update(policy));
	mutex_unlock(&policy_dbs->update_mutex);

	/* Allow the utilization update handler to queue up more work. */
	atomic_set(&policy_dbs->work_count, 0);
	/*
	 * If the update below is reordered with respect to the sample delay
	 * modification, the utilization update handler may end up using a stale
	 * sample delay value.
	 */
	smp_wmb();
	policy_dbs->work_in_progress = false;
}

// drivers/cpufreq/cpufreq_ondemand.c
// ondemand回调函数，按照CPU负载计算频率
static unsigned int od_dbs_update(struct cpufreq_policy *policy)
{
	struct policy_dbs_info *policy_dbs = policy->governor_data;
	struct dbs_data *dbs_data = policy_dbs->dbs_data;
	struct od_policy_dbs_info *dbs_info = to_dbs_info(policy_dbs);
	int sample_type = dbs_info->sample_type;

	/* Common NORMAL_SAMPLE setup */
	dbs_info->sample_type = OD_NORMAL_SAMPLE;
	/*
	 * OD_SUB_SAMPLE doesn't make sense if sample_delay_ns is 0, so ignore
	 * it then.
	 */
	if (sample_type == OD_SUB_SAMPLE && policy_dbs->sample_delay_ns > 0) {
		__cpufreq_driver_target(policy, dbs_info->freq_lo,
					CPUFREQ_RELATION_H);
		return dbs_info->freq_lo_delay_us;
	}

	od_update(policy);

	if (dbs_info->freq_lo) {
		/* Setup SUB_SAMPLE */
		dbs_info->sample_type = OD_SUB_SAMPLE;
		return dbs_info->freq_hi_delay_us;
	}

	return dbs_data->sampling_rate * policy_dbs->rate_mult;
}

/*
 * Every sampling_rate, we check, if current idle time is less than 20%
 * (default), then we try to increase frequency. Else, we adjust the frequency
 * proportional to load.
 */
// drivers/cpufreq/cpufreq_ondemand.c
// 根据CPU负载，调整频率
static void od_update(struct cpufreq_policy *policy)
{
	struct policy_dbs_info *policy_dbs = policy->governor_data;
	struct od_policy_dbs_info *dbs_info = to_dbs_info(policy_dbs);
	struct dbs_data *dbs_data = policy_dbs->dbs_data;
	struct od_dbs_tuners *od_tuners = dbs_data->tuners;
	unsigned int load = dbs_update(policy);

	dbs_info->freq_lo = 0;

	/* Check for frequency increase */
    // 检查当前的CPU负载，负载大于80%（也可以在sysfs中设置）
	if (load > dbs_data->up_threshold) {
		/* If switching to max speed, apply sampling_down_factor */
		if (policy->cur < policy->max)
			policy_dbs->rate_mult = dbs_data->sampling_down_factor;
		dbs_freq_increase(policy, policy->max);
	} else {
		/* Calculate the next frequency proportional to load */
		unsigned int freq_next, min_f, max_f;

		min_f = policy->cpuinfo.min_freq;
		max_f = policy->cpuinfo.max_freq;
        // 按照CPU负载计算调频频率
		freq_next = min_f + load * (max_f - min_f) / 100;

		/* No longer fully busy, reset rate_mult */
		policy_dbs->rate_mult = 1;

        // 为了进一步节省电力，在计算出的新频率上再乘以一个powersave_bias设定的百分比
        // powersave_bias的值从0-1000，每一步表示0.1%
		if (od_tuners->powersave_bias)
			freq_next = od_ops.powersave_bias_target(policy,
								 freq_next,
								 CPUFREQ_RELATION_L);
		// 频率调整
		__cpufreq_driver_target(policy, freq_next, CPUFREQ_RELATION_C);
	}
}

// drivers/cpufreq/cpufreq_governor.c
// 计算当前域CPU负载 cpu_load = 100 * (time_elapsed - idle_time) / time_elapsed
// 返回当前域中最大的CPU负载
unsigned int dbs_update(struct cpufreq_policy *policy)
{
	struct policy_dbs_info *policy_dbs = policy->governor_data;
	struct dbs_data *dbs_data = policy_dbs->dbs_data;
	unsigned int ignore_nice = dbs_data->ignore_nice_load;
	unsigned int max_load = 0, idle_periods = UINT_MAX;
	unsigned int sampling_rate, io_busy, j;

	/*
	 * Sometimes governors may use an additional multiplier to increase
	 * sample delays temporarily.  Apply that multiplier to sampling_rate
	 * so as to keep the wake-up-from-idle detection logic a bit
	 * conservative.
	 */
	sampling_rate = dbs_data->sampling_rate * policy_dbs->rate_mult;
	/*
	 * For the purpose of ondemand, waiting for disk IO is an indication
	 * that you're performance critical, and not that the system is actually
	 * idle, so do not add the iowait time to the CPU idle time then.
	 */
	io_busy = dbs_data->io_is_busy;

	/* Get Absolute Load */
    // 计算当前policy中CPU的最大负载
	for_each_cpu(j, policy->cpus) {
		struct cpu_dbs_info *j_cdbs = &per_cpu(cpu_dbs, j);
		u64 update_time, cur_idle_time;
		unsigned int idle_time, time_elapsed;
		unsigned int load;

        // 获取当前idle时间
		cur_idle_time = get_cpu_idle_time(j, &update_time, io_busy);

        // time_elapsed = 本次总运行时间 - 上次总运行时间
		time_elapsed = update_time - j_cdbs->prev_update_time;
		j_cdbs->prev_update_time = update_time;

		// 计算本次时间间隔内的idle_time
        // idle_time = 本次idle时间 - 上次idle时间
		idle_time = cur_idle_time - j_cdbs->prev_cpu_idle;
		j_cdbs->prev_cpu_idle = cur_idle_time;

		if (ignore_nice) {
			u64 cur_nice = kcpustat_field(&kcpustat_cpu(j), CPUTIME_NICE, j);

			idle_time += div_u64(cur_nice - j_cdbs->prev_cpu_nice, NSEC_PER_USEC);
			j_cdbs->prev_cpu_nice = cur_nice;
		}

		// 这里主要是对各种比较罕见的情况进行临时处理
		if (unlikely(!time_elapsed)) {
			/*
			 * That can only happen when this function is called
			 * twice in a row with a very short interval between the
			 * calls, so the previous load value can be used then.
			 */
			load = j_cdbs->prev_load;
		} else if (unlikely((int)idle_time > 2 * sampling_rate &&
				    j_cdbs->prev_load)) {
			/*
			 * If the CPU had gone completely idle and a task has
			 * just woken up on this CPU now, it would be unfair to
			 * calculate 'load' the usual way for this elapsed
			 * time-window, because it would show near-zero load,
			 * irrespective of how CPU intensive that task actually
			 * was. This is undesirable for latency-sensitive bursty
			 * workloads.
			 *
			 * To avoid this, reuse the 'load' from the previous
			 * time-window and give this task a chance to start with
			 * a reasonably high CPU frequency. However, that
			 * shouldn't be over-done, lest we get stuck at a high
			 * load (high frequency) for too long, even when the
			 * current system load has actually dropped down, so
			 * clear prev_load to guarantee that the load will be
			 * computed again next time.
			 *
			 * Detecting this situation is easy: an unusually large
			 * 'idle_time' (as compared to the sampling rate)
			 * indicates this scenario.
			 */
			load = j_cdbs->prev_load;
			j_cdbs->prev_load = 0;
		// 程序正常会运行到这里进行负载计算
		} else {
			if (time_elapsed >= idle_time) {
				load = 100 * (time_elapsed - idle_time) / time_elapsed;
			} else {
				/*
				 * That can happen if idle_time is returned by
				 * get_cpu_idle_time_jiffy().  In that case
				 * idle_time is roughly equal to the difference
				 * between time_elapsed and "busy time" obtained
				 * from CPU statistics.  Then, the "busy time"
				 * can end up being greater than time_elapsed
				 * (for example, if jiffies_64 and the CPU
				 * statistics are updated by different CPUs),
				 * so idle_time may in fact be negative.  That
				 * means, though, that the CPU was busy all
				 * the time (on the rough average) during the
				 * last sampling interval and 100 can be
				 * returned as the load.
				 */
				load = (int)idle_time < 0 ? 100 : 0;
			}
			j_cdbs->prev_load = load;
		}

		if (unlikely((int)idle_time > 2 * sampling_rate)) {
			unsigned int periods = idle_time / sampling_rate;

			if (periods < idle_periods)
				idle_periods = periods;
		}
		// 取当前policy中CPU负载最大的值
		if (load > max_load)
			max_load = load;
	}

	policy_dbs->idle_periods = idle_periods;

	return max_load;
}

schedutil调节器


sugov（schedutil governor）作为一种内核调频策略模块，它主要是根据当前CPU的利用率进行调频。因此，sugov会注册一个callback函数（sugov_update_shared/sugov_update_single)到调度器负载跟踪模块，当CPU util发生变化的时候就会调用该callback函数，检查一下当前CPU频率是否和当前的CPU util匹配，如果不匹配，那么就进行升频或者降频。

sugov_tunables结构体，用来描述sugov的可调参数

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// sugov_tunables结构体
struct sugov_tunables {
	struct gov_attr_set attr_set;
	// 目前sugov只有这一个可调参数，该参数用来限制连续调频的间隔时间
	unsigned int rate_limit_us;
};

sugov_policy结构体，sugov为每个cluster构建了该数据结构，记录每个cluster的调频数据信息

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// sugov_policy结构体，为每个簇构建了该数据结构，记录每个簇的调频数据信息
struct sugov_policy {
	// 指向cpufreq framework层的policy对象
	struct cpufreq_policy	*policy;
	// sugov的可调参数
	struct sugov_tunables	*tunables;
	struct list_head	tunables_hook;

	raw_spinlock_t		update_lock;	/* For shared policies */
	// 记录上次进行频率调整的时间点
	u64			last_freq_update_time;
	// 最小调频时间间隔
	s64			freq_update_delay_ns;
	// 下一个需要调整到的频率值，回调函数主要是计算这个参数
	unsigned int		next_freq;
	// 根据CPU util计算出来的原始频率，在频率表中向上找最接近的频率进行调整
	unsigned int		cached_raw_freq;

	/* The next fields are only needed if fast switch cannot be used: */
	struct			irq_work irq_work;
	struct			kthread_work work;
	struct			mutex work_lock;
	struct			kthread_worker worker;
	struct task_struct	*thread;
	bool			work_in_progress;

	bool			limits_changed;
	bool			need_freq_update;
};

sugov_cpu结构体，sugov为每个cpu构建了该数据结构，记录每个CPU的调频数据信息

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struct sugov_cpu {
	// 保存了cpu util变化后的回调函数
	struct update_util_data	update_util;
	// 该sugov_cpu对应的sugov_policy对象
	struct sugov_policy	*sg_policy;
	// 对应的CPU id
	unsigned int		cpu;

	bool			iowait_boost_pending;
	unsigned int		iowait_boost;
	// 上一次cpu负载变化驱动调频的时间点，util更新的时间点
	u64			last_update;

	unsigned long		bw_dl;
	// 该CPU的最大算力，即最大utilities，归一化到1024
	unsigned long		max;

	/* The field below is for single-CPU policies only: */
#ifdef CONFIG_NO_HZ_COMMON
	unsigned long		saved_idle_calls;
#endif
};

sugov初始化过程和ondemand初始化过程相似，当内核设定默认governor为sugov时，在cpufreq_init_governor(policy);中会调用sugov_init()初始化sugov，然后调用sugov_start()设置调频回调函数，每当CPU利用率发生变化的时候，调度器都会调用cpufreq_update_util()通知sugov，在cpufreq_update_util()被调用时，即任务调度后CPU当前的util发生变化，会调用sugov的回调函数进行调频，sugov_update_shared()当一个簇中有多个CPU调用该回调，遍历簇上的CPU找到当前最大util的CPU，然后根据该util映射到频率；sugov_update_single()即一个簇上单个CPU的情况直接根据该CPU util计算频率

调度事件的发生还是非常密集的，特别是在重载的情况下，很多任务可能执行若干个us就切换出去了。如果每次都计算CPU util看看是否需要调整频率，那么本身sugov就给系统带来较重的负荷，因此并非每次调频时机都会真正执行调频检查，sugov设置了一个最小调频间隔，小于这个间隔的调频请求会被过滤掉。

schedutil频率计算过程
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// sugov_start会遍历该sugov policy（cluster）中的所有cpu
// 调用cpufreq_add_update_util_hook为sugov cpu注册调频回调函数，代码逻辑如下：
static int sugov_start(struct cpufreq_policy *policy)
{
	...
	for_each_cpu(cpu, policy->cpus) {
		struct sugov_cpu *sg_cpu = &per_cpu(sugov_cpu, cpu);
		// 设置governor 计算回调函数，cpufreq_update_util()被调用时
		// 即任务调度后CPU当前的util发生变化，会调用sugov的回调函数进行调频计算
		cpufreq_add_update_util_hook(cpu, &sg_cpu->update_util,
					     policy_is_shared(policy) ?
							sugov_update_shared :
							sugov_update_single);
	}
	...
}

// schedutil频率计算过程
sugov_update_single();
	// 调频最小间隔时间检查，小于设定时间，直接返回
	sugov_should_update_freq();
	util = sugov_get_util(sg_cpuu);
		schedutil_cpu_util(sg_cpu->cpu, util, max, FREQUENCY_UTIL, NULL);
	// 根据当前CPU的util映射到具体的频率上
	next_f = get_next_freq(sg_policy, util, max);
	// 调用cpufreq_driver进行调频
	sugov_deferred_update(sg_policy, time, next_f);
		__cpufreq_driver_target()

// 计算cpu当前的utility
unsigned long schedutil_cpu_util(int cpu, unsigned long util_cfs,
					unsigned long max, enum schedutil_type type,
					struct task_struct *p)
{
	unsigned long dl_util, util, irq;
	struct rq *rq = cpu_rq(cpu);

	if (!uclamp_is_used() &&
	    type == FREQUENCY_UTIL && rt_rq_is_runnable(&rq->rt)) {
		return max;
	}

	// 如果CPU处理了过多的中断服务函数，irq负载已经高过CPU最大算力，直接返回最大算力
	irq = cpu_util_irq(rq);
	if (unlikely(irq >= max))
		return max;

	// 累加了cfs和rt任务的utility
	util = util_cfs + cpu_util_rt(rq);
	if (type == FREQUENCY_UTIL)
		util = uclamp_rq_util_with(rq, util, p);

	dl_util = cpu_util_dl(rq);

	if (util + dl_util >= max)
		return max;

	/*
	 * OTOH, for energy computation we need the estimated running time, so
	 * include util_dl and ignore dl_bw.
	 */
	if (type == ENERGY_UTIL)
		util += dl_util;

	/*
	 * There is still idle time; further improve the number by using the
	 * irq metric. Because IRQ/steal time is hidden from the task clock we
	 * need to scale the task numbers:
	 *
	 *              max - irq
	 *   U' = irq + --------- * U
	 *                 max
	 */
	// irq会偷走一部分的cpu算力，从而让其capacity没有那么大。
	// 这里通过scale_irq_capacity对任务的utility进行调整
	util = scale_irq_capacity(util, irq, max);
	util += irq;

	/*
	 * Bandwidth required by DEADLINE must always be granted while, for
	 * FAIR and RT, we use blocked utilization of IDLE CPUs as a mechanism
	 * to gracefully reduce the frequency when no tasks show up for longer
	 * periods of time.
	 *
	 * Ideally we would like to set bw_dl as min/guaranteed freq and util +
	 * bw_dl as requested freq. However, cpufreq is not yet ready for such
	 * an interface. So, we only do the latter for now.
	 */
	if (type == FREQUENCY_UTIL)
		util += cpu_bw_dl(rq);

	return min(max, util);
}

// 根据当前CPU计算的util映射对应频率
static unsigned int get_next_freq(struct sugov_policy *sg_policy,
				  unsigned long util, unsigned long max)
{
	struct cpufreq_policy *policy = sg_policy->policy;
	// 先取得当前CPU的最大频率
	unsigned int freq = arch_scale_freq_invariant() ?
				policy->cpuinfo.max_freq : policy->cur;
	// 计算当前util对应频率，计算公式: freq = (1.25) * freq * util / max
	// 这里冗余了25%的算力余量
	freq = map_util_freq(util, freq, max);

	// 若计算出的freq和上次缓存的一样，则实际调整的next_freq计算后肯定也是一样的，直接返回
	// 上次记录的频率值
	if (freq == sg_policy->cached_raw_freq && !sg_policy->need_freq_update)
		return sg_policy->next_freq;

	sg_policy->cached_raw_freq = freq;

	// 根据当前算的freq，在CPU频率表上查找对应的频率
	freq = cpufreq_driver_resolve_freq(policy, freq);

	return freq;
}

EAS能源感知调度

EAS整体框架

完全公平调度（Completely Fair Scheduler CFS）实现了面向吞吐量的的任务调度策略，EAS为这个调度器添加了一个基于能耗的调度策略，在优化CPU算力冗余的同时实现了节能，EAS在系统中、低度负载情况下工作，CFS在系统满负载情况下工作。

EAS在CPU调度领域，在为任务选核是起作用，目的是保证性能的情况下尽可能节省功耗，EAS涉及内核的几个子系统（任务调度、能源管理、CPU动态调频），EAS代码主要位于kernel/sched/fair.c，能源感知的任务调度需要调度器评估各个任务在CPU上运行带来的能耗影响

EAS全局控制开关/proc/sys/kernel/sched_energy_aware

CPU算力归一化过程

当前，Linux无法凭自身算出CPU算力，因此必须要有把这个信息传递给Linux的方式，它是从capacity-dmips-mhz CPU 设备树binding中衍生计算出来的

归一化CPU capacity，topology_normalize_cpu_scale()定义在drivers/base/arch_topology.c，这个capacity在schedutil调度中被sugov_get_util()函数读取

topology_normalize_cpu_scale()在CPU初始化parse_dt_topology()中被调用，capacity归一化的前提条件是需要在设备树中CPU节点设置capacity-dmips-mhz属性，该属性表示不同CPU的计算能力，内核读取该属性设置CPU的raw_capacity为capacity-dmips-mhz，参考内核文档Documentation/devicetree/bindings/arm/cpu-capacity.txt

ARM推荐的测试CPU的性能工具：Dhrystone 2.1以上版本，可以通过单核跑分成绩作为capacity-dmips-mhz属性的参考，DMIPS： Dhrystone Million Instructions executed Per Second，表示了在Dhrystone这样一种测试方法下的MIPS，Dhrystone是一种整数运算测试程序。MIPS/MHz，就是说每MHz频率能产生多大的MIPS，CPU性能通常由每秒百万指令（Millions of Instructions Per Second，MIPS）表示，设备树里表示为dmips/mhz

CPU算力归一化公式，并不是简单的将capacity-dmips-mhz归一化到capacity，CPU的频率也参与到了计算中

capacity = (own(capacity-dmips-mhz) * own(max_freq)) / (max(capacity-dmips-mhz) * max(max_freq)) * 1024

根据测试部测试的E2000QCPU单核性能数据，E2000Q的capacity-dmips-mhz属性值可以设置为如下，放大1000倍：

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// 小核
cpu_l0: cpu@0 {
	...
	capacity-dmips-mhz = <2850>;
	...
};
// 大核
cpu_b0: cpu@0 {
	...
	capacity-dmips-mhz = <5660>;
	...
};

实际经过CPU算力归一化到1024之后，对应的小核CPU算力为386，大核为1024

CPPC 调频驱动下的CPU算力归一化

在topology_init_cpu_capacity_cppc()中取得原始的CPU capacity数据，即 highest_perf，这个值是由固件描述的，之后还需要归一化到1024

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// arch/arm64/include/asm/topology.h
#ifdef CONFIG_ACPI_CPPC_LIB
#define arch_init_invariance_cppc topology_init_cpu_capacity_cppc
#endif

// drivers/acpi/cppc_acpi.c
__acpi_processor_start()
	acpi_cppc_processor_probe();
		arch_init_invariance_cppc(); -> topology_init_cpu_capacity_cppc();
			cppc_get_perf_caps(cpu, &perf_caps);

void topology_init_cpu_capacity_cppc(void)
{
	struct cppc_perf_caps perf_caps;
	int cpu;

	if (likely(!acpi_cpc_valid()))
		return;

	raw_capacity = kcalloc(num_possible_cpus(), sizeof(*raw_capacity),
			       GFP_KERNEL);
	if (!raw_capacity)
		return;

	for_each_possible_cpu(cpu) {
		if (!cppc_get_perf_caps(cpu, &perf_caps) &&
		    (perf_caps.highest_perf >= perf_caps.nominal_perf) &&
		    (perf_caps.highest_perf >= perf_caps.lowest_perf)) {
			raw_capacity[cpu] = perf_caps.highest_perf;
			pr_debug("cpu_capacity: CPU%d cpu_capacity=%u (raw).\n",
				 cpu, raw_capacity[cpu]);
			continue;
		}

		pr_err("cpu_capacity: CPU%d missing/invalid highest performance.\n", cpu);
		pr_err("cpu_capacity: partial information: fallback to 1024 for all CPUs\n");
		goto exit;
	}

	topology_normalize_cpu_scale();
	schedule_work(&update_topology_flags_work);
	pr_debug("cpu_capacity: cpu_capacity initialization done\n");

exit:
	free_raw_capacity();
}

查看 D3000M 的 highest_perf 值，可以看到固件那边并未设置为实际的 CPU 算力：

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root@Ubuntu:/sys/devices/system/cpu/cpu7/acpi_cppc# cat highest_perf 
2800

CPPC 调频驱动下的 perf domian 建立过程

perf domain 的 debug fs 路径： /sys/kernel/debug/energy_model/

D3000M perf domain 打印

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[    6.635761] freq: 400000, power: 7, cost: 7
[    6.635775] freq: 432000, power: 8, cost: 8
[    6.635790] freq: 486000, power: 9, cost: 9
[    6.635802] freq: 540000, power: 10, cost: 10
[    6.635819] freq: 594000, power: 11, cost: 11
[    6.635830] freq: 648000, power: 12, cost: 12
[    6.635841] freq: 702000, power: 13, cost: 13
[    6.635853] freq: 756000, power: 14, cost: 14
[    6.635864] freq: 810000, power: 15, cost: 15
[    6.635880] freq: 864000, power: 16, cost: 16
[    6.635892] freq: 918000, power: 17, cost: 17
[    6.635902] freq: 972000, power: 18, cost: 18
[    6.635913] freq: 1026000, power: 19, cost: 19
[    6.635924] freq: 1080000, power: 20, cost: 20
[    6.635941] freq: 1134000, power: 21, cost: 21
[    6.635951] freq: 1188000, power: 22, cost: 22
[    6.635962] freq: 1242000, power: 23, cost: 23
[    6.635973] freq: 1296000, power: 24, cost: 24
[    6.635984] freq: 1350000, power: 25, cost: 25
[    6.635997] freq: 1404000, power: 26, cost: 26
[    6.636008] freq: 1458000, power: 27, cost: 27
[    6.636019] freq: 1512000, power: 28, cost: 28
[    6.636030] freq: 1566000, power: 29, cost: 29
[    6.636041] freq: 1620000, power: 30, cost: 30
[    6.636051] freq: 1674000, power: 31, cost: 31
[    6.636066] freq: 1728000, power: 32, cost: 32
[    6.636076] freq: 1782000, power: 33, cost: 33
[    6.636087] freq: 1836000, power: 34, cost: 34
[    6.636098] freq: 1890000, power: 35, cost: 35
[    6.636108] freq: 1944000, power: 36, cost: 36
[    6.636122] freq: 1998000, power: 37, cost: 37
[    6.636133] freq: 2052000, power: 38, cost: 38
[    6.636143] freq: 2106000, power: 39, cost: 39
[    6.636153] freq: 2200000, power: 40, cost: 40
[    6.636156] processor cpu0: EM: created perf domain
[    6.637040] build_perf_domains
[    6.642544] ACPI CPPC: highest_perf: 2200, lowest_perf: 400
[    6.644473] freq: 400000, power: 7, cost: 7
[    6.644486] freq: 432000, power: 8, cost: 8
[    6.644497] freq: 486000, power: 9, cost: 9
[    6.644508] freq: 540000, power: 10, cost: 10
[    6.644523] freq: 594000, power: 11, cost: 11
[    6.644534] freq: 648000, power: 12, cost: 12
[    6.644545] freq: 702000, power: 13, cost: 13
[    6.644558] freq: 756000, power: 14, cost: 14
[    6.644569] freq: 810000, power: 15, cost: 15
[    6.644583] freq: 864000, power: 16, cost: 16
[    6.644595] freq: 918000, power: 17, cost: 17
[    6.644605] freq: 972000, power: 18, cost: 18
[    6.644616] freq: 1026000, power: 19, cost: 19
[    6.644627] freq: 1080000, power: 20, cost: 20
[    6.644638] freq: 1134000, power: 21, cost: 21
[    6.644652] freq: 1188000, power: 22, cost: 22
[    6.644663] freq: 1242000, power: 23, cost: 23
[    6.644674] freq: 1296000, power: 24, cost: 24
[    6.644685] freq: 1350000, power: 25, cost: 25
[    6.644696] freq: 1404000, power: 26, cost: 26
[    6.644709] freq: 1458000, power: 27, cost: 27
[    6.644720] freq: 1512000, power: 28, cost: 28
[    6.644733] freq: 1566000, power: 29, cost: 29
[    6.644744] freq: 1620000, power: 30, cost: 30
[    6.644754] freq: 1674000, power: 31, cost: 31
[    6.644768] freq: 1728000, power: 32, cost: 32
[    6.644779] freq: 1782000, power: 33, cost: 33
[    6.644791] freq: 1836000, power: 34, cost: 34
[    6.644801] freq: 1890000, power: 35, cost: 35
[    6.644812] freq: 1944000, power: 36, cost: 36
[    6.644827] freq: 1998000, power: 37, cost: 37
[    6.644837] freq: 2052000, power: 38, cost: 38
[    6.644848] freq: 2106000, power: 39, cost: 39
[    6.644859] freq: 2200000, power: 40, cost: 40
[    6.644862] processor cpu1: EM: created perf domain
[    6.644953] build_perf_domains
[    6.650568] ACPI CPPC: highest_perf: 2200, lowest_perf: 400
[    6.651553] freq: 400000, power: 7, cost: 7
[    6.651565] freq: 432000, power: 8, cost: 8
[    6.651572] freq: 486000, power: 9, cost: 9
[    6.651578] freq: 540000, power: 10, cost: 10
[    6.651585] freq: 594000, power: 11, cost: 11
[    6.651591] freq: 648000, power: 12, cost: 12
[    6.651597] freq: 702000, power: 13, cost: 13
[    6.651606] freq: 756000, power: 14, cost: 14
[    6.651613] freq: 810000, power: 15, cost: 15
[    6.651619] freq: 864000, power: 16, cost: 16
[    6.651625] freq: 918000, power: 17, cost: 17
[    6.651631] freq: 972000, power: 18, cost: 18
[    6.651639] freq: 1026000, power: 19, cost: 19
[    6.651645] freq: 1080000, power: 20, cost: 20
[    6.651653] freq: 1134000, power: 21, cost: 21
[    6.651659] freq: 1188000, power: 22, cost: 22
[    6.651665] freq: 1242000, power: 23, cost: 23
[    6.651673] freq: 1296000, power: 24, cost: 24
[    6.651679] freq: 1350000, power: 25, cost: 25
[    6.651685] freq: 1404000, power: 26, cost: 26
[    6.651691] freq: 1458000, power: 27, cost: 27
[    6.651697] freq: 1512000, power: 28, cost: 28
[    6.651706] freq: 1566000, power: 29, cost: 29
[    6.651712] freq: 1620000, power: 30, cost: 30
[    6.651718] freq: 1674000, power: 31, cost: 31
[    6.651724] freq: 1728000, power: 32, cost: 32
[    6.651730] freq: 1782000, power: 33, cost: 33
[    6.651739] freq: 1836000, power: 34, cost: 34
[    6.651745] freq: 1890000, power: 35, cost: 35
[    6.651750] freq: 1944000, power: 36, cost: 36
[    6.651756] freq: 1998000, power: 37, cost: 37
[    6.651762] freq: 2052000, power: 38, cost: 38
[    6.651768] freq: 2106000, power: 39, cost: 39
[    6.651776] freq: 2200000, power: 40, cost: 40
[    6.651778] processor cpu2: EM: created perf domain
[    6.651845] build_perf_domains
[    6.652531] phytium-qspi PHYT0011:00: capacity register(0x00) is the latest design
[    6.656115] ACPI CPPC: highest_perf: 2800, lowest_perf: 400
[    6.657948] freq: 400000, power: 211, cost: 211
[    6.657960] freq: 432000, power: 212, cost: 212
[    6.657967] freq: 486000, power: 213, cost: 213
[    6.657974] freq: 540000, power: 214, cost: 214
[    6.657981] freq: 594000, power: 215, cost: 215
[    6.657988] freq: 648000, power: 216, cost: 216
[    6.657998] freq: 702000, power: 217, cost: 217
[    6.658005] freq: 756000, power: 218, cost: 218
[    6.658012] freq: 810000, power: 219, cost: 219
[    6.658019] freq: 864000, power: 220, cost: 220
[    6.658025] freq: 918000, power: 221, cost: 221
[    6.658035] freq: 972000, power: 222, cost: 222
[    6.658043] freq: 1026000, power: 223, cost: 223
[    6.658050] freq: 1080000, power: 224, cost: 224
[    6.658057] freq: 1134000, power: 225, cost: 225
[    6.658064] freq: 1188000, power: 226, cost: 226
[    6.658075] freq: 1242000, power: 227, cost: 227
[    6.658081] freq: 1296000, power: 228, cost: 228
[    6.658088] freq: 1350000, power: 229, cost: 229
[    6.658095] freq: 1404000, power: 230, cost: 230
[    6.658102] freq: 1458000, power: 231, cost: 231
[    6.658109] freq: 1512000, power: 232, cost: 232
[    6.658119] freq: 1566000, power: 233, cost: 233
[    6.658126] freq: 1620000, power: 234, cost: 234
[    6.658133] freq: 1674000, power: 235, cost: 235
[    6.658140] freq: 1728000, power: 236, cost: 236
[    6.658147] freq: 1782000, power: 237, cost: 237
[    6.658156] freq: 1836000, power: 238, cost: 238
[    6.658163] freq: 1890000, power: 239, cost: 239
[    6.658170] freq: 1944000, power: 240, cost: 240
[    6.658176] freq: 1998000, power: 241, cost: 241
[    6.658185] freq: 2052000, power: 242, cost: 242
[    6.658195] freq: 2106000, power: 243, cost: 243
[    6.658202] freq: 2160000, power: 244, cost: 244
[    6.658209] freq: 2214000, power: 245, cost: 245
[    6.658216] freq: 2268000, power: 246, cost: 246
[    6.658222] freq: 2322000, power: 247, cost: 247
[    6.658232] freq: 2376000, power: 248, cost: 248
[    6.658240] freq: 2430000, power: 249, cost: 249
[    6.658247] freq: 2484000, power: 250, cost: 250
[    6.658255] freq: 2538000, power: 251, cost: 251
[    6.658261] freq: 2592000, power: 252, cost: 252
[    6.658272] freq: 2646000, power: 253, cost: 253
[    6.658280] freq: 2700000, power: 254, cost: 254
[    6.658286] freq: 2800000, power: 255, cost: 255
[    6.658288] processor cpu3: EM: created perf domain
[    6.658378] build_perf_domains
[    6.660667] ACPI CPPC: highest_perf: 2200, lowest_perf: 400
[    6.661397] freq: 400000, power: 415, cost: 415
[    6.661406] freq: 432000, power: 416, cost: 416
[    6.661414] freq: 486000, power: 417, cost: 417
[    6.661422] freq: 540000, power: 418, cost: 418
[    6.661429] freq: 594000, power: 419, cost: 419
[    6.661437] freq: 648000, power: 420, cost: 420
[    6.661444] freq: 702000, power: 421, cost: 421
[    6.661450] freq: 756000, power: 422, cost: 422
[    6.661458] freq: 810000, power: 423, cost: 423
[    6.661466] freq: 864000, power: 424, cost: 424
[    6.661474] freq: 918000, power: 425, cost: 425
[    6.661481] freq: 972000, power: 426, cost: 426
[    6.661493] freq: 1026000, power: 427, cost: 427
[    6.661500] freq: 1080000, power: 428, cost: 428
[    6.661507] freq: 1134000, power: 429, cost: 429
[    6.661513] freq: 1188000, power: 430, cost: 430
[    6.661520] freq: 1242000, power: 431, cost: 431
[    6.661529] freq: 1296000, power: 432, cost: 432
[    6.661536] freq: 1350000, power: 433, cost: 433
[    6.661542] freq: 1404000, power: 434, cost: 434
[    6.661549] freq: 1458000, power: 435, cost: 435
[    6.661555] freq: 1512000, power: 436, cost: 436
[    6.661564] freq: 1566000, power: 437, cost: 437
[    6.661570] freq: 1620000, power: 438, cost: 438
[    6.661576] freq: 1674000, power: 439, cost: 439
[    6.661584] freq: 1728000, power: 440, cost: 440
[    6.661590] freq: 1782000, power: 441, cost: 441
[    6.661596] freq: 1836000, power: 442, cost: 442
[    6.661605] freq: 1890000, power: 443, cost: 443
[    6.661612] freq: 1944000, power: 444, cost: 444
[    6.661618] freq: 1998000, power: 445, cost: 445
[    6.661625] freq: 2052000, power: 446, cost: 446
[    6.661632] freq: 2106000, power: 447, cost: 447
[    6.661640] freq: 2200000, power: 448, cost: 448
[    6.661642] processor cpu4: EM: created perf domain
[    6.661744] build_perf_domains
[    6.665962] ACPI CPPC: highest_perf: 2200, lowest_perf: 400
[    6.668778] freq: 400000, power: 415, cost: 415
[    6.668787] freq: 432000, power: 416, cost: 416
[    6.668796] freq: 486000, power: 417, cost: 417
[    6.668807] freq: 540000, power: 418, cost: 418
[    6.668814] freq: 594000, power: 419, cost: 419
[    6.668821] freq: 648000, power: 420, cost: 420
[    6.668827] freq: 702000, power: 421, cost: 421
[    6.668834] freq: 756000, power: 422, cost: 422
[    6.668843] freq: 810000, power: 423, cost: 423
[    6.668850] freq: 864000, power: 424, cost: 424
[    6.668857] freq: 918000, power: 425, cost: 425
[    6.668864] freq: 972000, power: 426, cost: 426
[    6.668871] freq: 1026000, power: 427, cost: 427
[    6.668878] freq: 1080000, power: 428, cost: 428
[    6.668887] freq: 1134000, power: 429, cost: 429
[    6.668893] freq: 1188000, power: 430, cost: 430
[    6.668900] freq: 1242000, power: 431, cost: 431
[    6.668906] freq: 1296000, power: 432, cost: 432
[    6.668913] freq: 1350000, power: 433, cost: 433
[    6.668923] freq: 1404000, power: 434, cost: 434
[    6.668929] freq: 1458000, power: 435, cost: 435
[    6.668936] freq: 1512000, power: 436, cost: 436
[    6.668943] freq: 1566000, power: 437, cost: 437
[    6.668950] freq: 1620000, power: 438, cost: 438
[    6.668959] freq: 1674000, power: 439, cost: 439
[    6.668966] freq: 1728000, power: 440, cost: 440
[    6.668973] freq: 1782000, power: 441, cost: 441
[    6.668980] freq: 1836000, power: 442, cost: 442
[    6.668986] freq: 1890000, power: 443, cost: 443
[    6.668995] freq: 1944000, power: 444, cost: 444
[    6.669003] freq: 1998000, power: 445, cost: 445
[    6.669010] freq: 2052000, power: 446, cost: 446
[    6.669016] freq: 2106000, power: 447, cost: 447
[    6.669023] freq: 2200000, power: 448, cost: 448
[    6.669025] processor cpu5: EM: created perf domain
[    6.669894] build_perf_domains
[    6.671484] ACPI CPPC: highest_perf: 2200, lowest_perf: 400
[    6.672099] freq: 400000, power: 415, cost: 415
[    6.672109] freq: 432000, power: 416, cost: 416
[    6.672116] freq: 486000, power: 417, cost: 417
[    6.672124] freq: 540000, power: 418, cost: 418
[    6.672134] freq: 594000, power: 419, cost: 419
[    6.672141] freq: 648000, power: 420, cost: 420
[    6.672148] freq: 702000, power: 421, cost: 421
[    6.672155] freq: 756000, power: 422, cost: 422
[    6.672162] freq: 810000, power: 423, cost: 423
[    6.672171] freq: 864000, power: 424, cost: 424
[    6.672178] freq: 918000, power: 425, cost: 425
[    6.672184] freq: 972000, power: 426, cost: 426
[    6.672191] freq: 1026000, power: 427, cost: 427
[    6.672199] freq: 1080000, power: 428, cost: 428
[    6.672206] freq: 1134000, power: 429, cost: 429
[    6.672215] freq: 1188000, power: 430, cost: 430
[    6.672222] freq: 1242000, power: 431, cost: 431
[    6.672229] freq: 1296000, power: 432, cost: 432
[    6.672237] freq: 1350000, power: 433, cost: 433
[    6.672244] freq: 1404000, power: 434, cost: 434
[    6.672253] freq: 1458000, power: 435, cost: 435
[    6.672260] freq: 1512000, power: 436, cost: 436
[    6.672267] freq: 1566000, power: 437, cost: 437
[    6.672274] freq: 1620000, power: 438, cost: 438
[    6.672281] freq: 1674000, power: 439, cost: 439
[    6.672293] freq: 1728000, power: 440, cost: 440
[    6.672300] freq: 1782000, power: 441, cost: 441
[    6.672307] freq: 1836000, power: 442, cost: 442
[    6.672314] freq: 1890000, power: 443, cost: 443
[    6.672321] freq: 1944000, power: 444, cost: 444
[    6.672330] freq: 1998000, power: 445, cost: 445
[    6.672337] freq: 2052000, power: 446, cost: 446
[    6.672344] freq: 2106000, power: 447, cost: 447
[    6.672350] freq: 2200000, power: 448, cost: 448
[    6.672352] processor cpu6: EM: created perf domain
[    6.672434] build_perf_domains
[    6.674139] ACPI CPPC: highest_perf: 2800, lowest_perf: 400
[    6.676465] freq: 400000, power: 619, cost: 619
[    6.676477] freq: 432000, power: 620, cost: 620
[    6.676484] freq: 486000, power: 621, cost: 621
[    6.676491] freq: 540000, power: 622, cost: 622
[    6.676499] freq: 594000, power: 623, cost: 623
[    6.676506] freq: 648000, power: 624, cost: 624
[    6.676515] freq: 702000, power: 625, cost: 625
[    6.676524] freq: 756000, power: 626, cost: 626
[    6.676530] freq: 810000, power: 627, cost: 627
[    6.676537] freq: 864000, power: 628, cost: 628
[    6.676545] freq: 918000, power: 629, cost: 629
[    6.676554] freq: 972000, power: 630, cost: 630
[    6.676561] freq: 1026000, power: 631, cost: 631
[    6.676568] freq: 1080000, power: 632, cost: 632
[    6.676574] freq: 1134000, power: 633, cost: 633
[    6.676580] freq: 1188000, power: 634, cost: 634
[    6.676589] freq: 1242000, power: 635, cost: 635
[    6.676596] freq: 1296000, power: 636, cost: 636
[    6.676603] freq: 1350000, power: 637, cost: 637
[    6.676609] freq: 1404000, power: 638, cost: 638
[    6.676616] freq: 1458000, power: 639, cost: 639
[    6.676624] freq: 1512000, power: 640, cost: 640
[    6.676634] freq: 1566000, power: 641, cost: 641
[    6.676641] freq: 1620000, power: 642, cost: 642
[    6.676648] freq: 1674000, power: 643, cost: 643
[    6.676655] freq: 1728000, power: 644, cost: 644
[    6.676662] freq: 1782000, power: 645, cost: 645
[    6.676671] freq: 1836000, power: 646, cost: 646
[    6.676678] freq: 1890000, power: 647, cost: 647
[    6.676686] freq: 1944000, power: 648, cost: 648
[    6.676692] freq: 1998000, power: 649, cost: 649
[    6.676699] freq: 2052000, power: 650, cost: 650
[    6.676708] freq: 2106000, power: 651, cost: 651
[    6.676715] freq: 2160000, power: 652, cost: 652
[    6.676721] freq: 2214000, power: 653, cost: 653
[    6.676728] freq: 2268000, power: 654, cost: 654
[    6.676734] freq: 2322000, power: 655, cost: 655
[    6.676743] freq: 2376000, power: 656, cost: 656
[    6.676750] freq: 2430000, power: 657, cost: 657
[    6.676756] freq: 2484000, power: 658, cost: 658
[    6.676763] freq: 2538000, power: 659, cost: 659
[    6.676770] freq: 2592000, power: 660, cost: 660
[    6.676780] freq: 2646000, power: 661, cost: 661
[    6.676786] freq: 2700000, power: 662, cost: 662
[    6.676793] freq: 2800000, power: 663, cost: 663
[    6.676795] processor cpu7: EM: created perf domain

EAS代码相关结构体

perf_domain结构表示一个CPU性能域，perf_domain和cpufreq_policy是一一对应的，性能域之间形成链，链表头存放在root_domain中

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// kernel/sched/sched.h
// perf_comain 结构表示一个CPU性能域，perf_domain和cpufreq_policy是一一对应的
struct perf_domain {
	struct em_perf_domain *em_pd;
	struct perf_domain *next;
	struct rcu_head rcu;
};

// cpumask_var_t解析
// include/uapi/linux/kernel.h
#define __KERNEL_DIV_ROUND_UP(n, d) ((((n) + (d)) - 1) / (d))

// include/linux/kernel.h
#define DIV_ROUND_UP	__KERNEL_DIV_ROUND_UP

// include/linux/bits.h
#define BITS_PER_BYTE 	8

// include/linux/bitops.h
#define BITS_PER_TYPE(type) (sizeof(type) * BITS_PER_BYTE)
#define BITS_TO_LONGS(nr)	DIV_ROUND_UP(nr, BITS_PER_TYPE(long))

// include/linux/types.h
#define DECLARE_BITMAP(name, bits) \
	unsigned long name[BITS_TO_LONGS(bits)]

// include/linux/threads.h
#define CONFIG_NR_CPUS 256
#define NR_CPUS		CONFIG_NR_CPUS

// include/linux/cpumask.h
typedef struct cpumask { DECLARE_BITMAP(bits, NR_CPUS); } cpumask_t;
typedef struct cpumask cpumask_var_t[1];

// 展开cpumask
// 该结构体用来表示当前系统中CPU的状态，每个CPU对应其中一位
// 这里内核配置最大支持256个CPU，所以定义了一个长度为4的long数组
typedef struct cpumask {
	/*
	unsigned long bits[BITS_TO_LONGS(256)];
	unsigned long bits[DIV_ROUND_UP(256, 64)];
	*/
	unsigned long bits[4];
} cpumask_t;

// root_domain代表CPU性能域的一个总体数据结构，管理这些性能域
struct root_domain {
	atomic_t		refcount;
	atomic_t		rto_count;
	struct rcu_head		rcu;
	cpumask_var_t		span;
	cpumask_var_t		online;

	// 该root_domain是否处于overload状态
	int			overload;

	// 该root_domain是否处于overutilized状态
	int			overutilized;

	/*
	 * The bit corresponding to a CPU gets set here if such CPU has more
	 * than one runnable -deadline task (as it is below for RT tasks).
	 */
	cpumask_var_t		dlo_mask;
	atomic_t		dlo_count;
	struct dl_bw		dl_bw;
	struct cpudl		cpudl;

#ifdef HAVE_RT_PUSH_IPI
	/*
	 * For IPI pull requests, loop across the rto_mask.
	 */
	struct irq_work		rto_push_work;
	raw_spinlock_t		rto_lock;
	/* These are only updated and read within rto_lock */
	int			rto_loop;
	int			rto_cpu;
	/* These atomics are updated outside of a lock */
	atomic_t		rto_loop_next;
	atomic_t		rto_loop_start;
#endif
	/*
	 * The "RT overload" flag: it gets set if a CPU has more than
	 * one runnable RT task.
	 */
	cpumask_var_t		rto_mask;
	struct cpupri		cpupri;

	// 系统中算力最大的CPU的算力
	unsigned long		max_cpu_capacity;

	/*
	 * NULL-terminated list of performance domains intersecting with the
	 * CPUs of the rd. Protected by RCU.
	 */
	// perf_domain单链表的表头
	struct perf_domain __rcu *pd;
};

// include/linux/energy_model.h
struct em_perf_state {
	unsigned long frequency;	// CPU频点，单位KHz
	unsigned long power;		// 此频点下的功耗
	unsigned long cost;			// 此频点下的成本系数，等于 power * max_freq / freq
};

struct em_perf_domain {
	struct em_perf_state *table;	// CPU频点表
	int nr_perf_states;				// 频点表中元素的个数
	unsigned long cpus[];			// 此性能域中包括哪些CPU
};

perf_domain初始化

start_kernel() -> sched_init() -> init_defrootdomain()

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// kernel/sched/core.c
void __init sched_init(void)
{
	...
#ifdef CONFIG_SMP
	init_defrootdmain();
#endif
	...
}

// kernel/sched/topology.c
static bool build_perf_domains(const struct cpumask *cpu_map)
{
	// 这里nr_cpus即统计cpu_map里面当前CPU的个数
	int i, nr_pd = 0, nr_ps = 0, nr_cpus = cpumask_weight(cpu_map);
	struct perf_domain *pd = NULL, *tmp;
	int cpu = cpumask_first(cpu_map);
	struct root_domain *rd = cpu_rq(cpu)->rd;
	struct cpufreq_policy *policy;
	struct cpufreq_governor *gov;

	if (!sysctl_sched_energy_aware)
		goto free;

	/* EAS is enabled for asymmetric CPU capacity topologies. */
	if (!per_cpu(sd_asym_cpucapacity, cpu)) {
		if (sched_debug()) {
			pr_info("rd %*pbl: CPUs do not have asymmetric capacities\n",
					cpumask_pr_args(cpu_map));
		}
		goto free;
	}

	/* EAS definitely does *not* handle SMT */
	if (sched_smt_active()) {
		pr_warn("rd %*pbl: Disabling EAS, SMT is not supported\n",
			cpumask_pr_args(cpu_map));
		goto free;
	}

	for_each_cpu(i, cpu_map) {
		/* Skip already covered CPUs. */
		if (find_pd(pd, i))
			continue;

		/* Do not attempt EAS if schedutil is not being used. */
		policy = cpufreq_cpu_get(i);
		if (!policy)
			goto free;
		gov = policy->governor;
		cpufreq_cpu_put(policy);
		if (gov != &schedutil_gov) {
			if (rd->pd)
				pr_warn("rd %*pbl: Disabling EAS, schedutil is mandatory\n",
						cpumask_pr_args(cpu_map));
			goto free;
		}

		/* Create the new pd and add it to the local list. */
		tmp = pd_init(i);
		if (!tmp)
			goto free;
		tmp->next = pd;
		pd = tmp;

		/*
		 * Count performance domains and performance states for the
		 * complexity check.
		 */
		nr_pd++;
		nr_ps += em_pd_nr_perf_states(pd->em_pd);
	}

	/* Bail out if the Energy Model complexity is too high. */
	if (nr_pd * (nr_ps + nr_cpus) > EM_MAX_COMPLEXITY) {
		WARN(1, "rd %*pbl: Failed to start EAS, EM complexity is too high\n",
						cpumask_pr_args(cpu_map));
		goto free;
	}

	perf_domain_debug(cpu_map, pd);

	/* Attach the new list of performance domains to the root domain. */
	tmp = rd->pd;
	rcu_assign_pointer(rd->pd, pd);
	if (tmp)
		call_rcu(&tmp->rcu, destroy_perf_domain_rcu);

	return !!pd;

free:
	free_pd(pd);
	tmp = rd->pd;
	rcu_assign_pointer(rd->pd, NULL);
	if (tmp)
		call_rcu(&tmp->rcu, destroy_perf_domain_rcu);

	return false;

}

E2000Q 5.10内核，perf_domain_debug 打印信息

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[    2.574534] root_domain 0-3: pd3:{ cpus=3 nr_pstate=4 }
[    2.574540] freq: 250000, power: 79, cost: 632
[    2.579072] freq: 500000, power: 197, cost: 788
[    2.583690] freq: 1000000, power: 409, cost: 818
[    2.588390] freq: 2000000, power: 839, cost: 839
[    2.593094]  pd2:{ cpus=2 nr_pstate=4 }
[    2.593096] freq: 250000, power: 79, cost: 632
[    2.601445] freq: 500000, power: 197, cost: 788
[    2.606054] freq: 1000000, power: 409, cost: 818
[    2.610749] freq: 2000000, power: 839, cost: 839
[    2.615445]  pd0:{ cpus=0-1 nr_pstate=4 }
[    2.615447] freq: 187500, power: 1, cost: 8
[    2.623709] freq: 375000, power: 9, cost: 36
[    2.628058] freq: 750000, power: 55, cost: 110
[    2.632579] freq: 1500000, power: 125, cost: 125

root_domain的overload和overutilized说明：

  • 对于一个 CPU 而言，其处于 overload 状态则说明其 rq 上有大于等于2个任务
  • 对于一个 CPU 而言，其处于 overutilized 状态说明该 cpu 的 utility 超过其 capacity（缺省预留20%的算力，另外，这里的 capacity 是用于cfs任务的算力）
  • 对于 root domain，overload 表示至少有一个 cpu 处于 overload 状态。overutilized 表示至少有一个 cpu 处于 overutilized 状态
  • overutilized 状态非常重要，它决定了调度器是否启用EAS，只有在系统没有 overutilized 的情况下EAS才会生效。overload和newidle balance的频次控制相关，当系统在overload的情况下，newidle balance才会启动进行均衡。

EAS能量计算方法

CPU在某个performance state(ps)下的计算能力：
ps->cap = ps->freq * scale_cpu / cpu_max_freq （1）

CPU在该频点performace state(ps)下的能量消耗：
cpu_nrg = ps->power * cpu_util / ps->cap （2）

结合(1) (2)可以得出CPU在该ps下的能量消耗
cpu_nrg = ps->power * cpu_max_freq * cpu_util / ps->freq * scale_cpu (3)

其中 ps->power * cpu_max_freq / ps->freq 是一个固定数据存放在频点表的cost成员中

一个pd内的CPU，拥有相同的cost，所以一个pd内所有CPU的能量消耗可以表示为
pd_nrg = ps->cost * sum(cpu_util) / scale_cpu

EAS的调度过程

在任务被重新唤醒或者fork新建时，会通过select_task_rq_fair()将任务进行balance，达到充分利用CPU的目的。在select_task_rq_fair()，若任务是被重新唤醒就会调用find_energy_efficient_cpu()进行选核执行

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/*
 * Predicts what cpu_util(@cpu) would return if @p was migrated (and enqueued)
 * to @dst_cpu.
 */
static unsigned long cpu_util_next(int cpu, struct task_struct *p, int dst_cpu)
{
	struct cfs_rq *cfs_rq = &cpu_rq(cpu)->cfs;
	// 计算cfs的util
	unsigned long util_est, util = READ_ONCE(cfs_rq->avg.util_avg);

	/*
	 * If @p migrates from @cpu to another, remove its contribution. Or,
	 * if @p migrates from another CPU to @cpu, add its contribution. In
	 * the other cases, @cpu is not impacted by the migration, so the
	 * util_avg should already be correct.
	 */
	// 在dst_cpu为-1的情况下
	// 若任务p运行在传入的CPU util = cfs_util - task_util(p)
	if (task_cpu(p) == cpu && dst_cpu != cpu)
		sub_positive(&util, task_util(p));
	else if (task_cpu(p) != cpu && dst_cpu == cpu)
		util += task_util(p);

	if (sched_feat(UTIL_EST)) {
		util_est = READ_ONCE(cfs_rq->avg.util_est.enqueued);

		/*
		 * During wake-up, the task isn't enqueued yet and doesn't
		 * appear in the cfs_rq->avg.util_est.enqueued of any rq,
		 * so just add it (if needed) to "simulate" what will be
		 * cpu_util() after the task has been enqueued.
		 */
		if (dst_cpu == cpu)
			util_est += _task_util_est(p);

		util = max(util, util_est);
	}

	return min(util, capacity_orig_of(cpu));
}


/*
 * compute_energy(): Estimates the energy that @pd would consume if @p was
 * migrated to @dst_cpu. compute_energy() predicts what will be the utilization
 * landscape of @pd's CPUs after the task migration, and uses the Energy Model
 * to compute what would be the energy if we decided to actually migrate that
 * task.
 */
// 计算任务迁移到dst_cpu后，整个pd，即此cluster的energy
static long
compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd)
{
	struct cpumask *pd_mask = perf_domain_span(pd);
	// 获取该CPU的算力，这里取得的是归一化到1024的算力
	unsigned long cpu_cap = arch_scale_cpu_capacity(cpumask_first(pd_mask));
	unsigned long max_util = 0, sum_util = 0;
	int cpu;

	// 对此pd中每个online cpu都执行计算
	for_each_cpu_and(cpu, pd_mask, cpu_online_mask) {
		// 这里计算util_cfs，当dst_cpu传入为-1时，这里是没将p的util计算进去的
		// 这个地方比较关键，p的util有没有算到cpu的util里面去是在这一步决定的
		unsigned long cpu_util, util_cfs = cpu_util_next(cpu, p, dst_cpu);
		struct task_struct *tsk = cpu == dst_cpu ? p : NULL;

		// 返回该CPU下cfs+irq+rt+dl使用掉的CPU算力总和
		// 这一步计算没将任务p的util加进去
		sum_util += schedutil_cpu_util(cpu, util_cfs, cpu_cap,
					       ENERGY_UTIL, NULL);
		// 这一步计算将任务p的util加进去了
		// 这里计算cpu_util的原因就是需要预测下一次该perf_domain的频率
		// 计算的cpu_util是略微放大了的，需要进一步分析这个放大的操作
		cpu_util = schedutil_cpu_util(cpu, util_cfs, cpu_cap,
					      FREQUENCY_UTIL, tsk);
		max_util = max(max_util, cpu_util);
	}

	// 计算该pd下所有CPU的功耗和
	return em_cpu_energy(pd->em_pd, max_util, sum_util);
}

// 计算该pd下所有CPU的功耗和
static inline unsigned long em_cpu_energy(struct em_perf_domain *pd,
				unsigned long max_util, unsigned long sum_util)
{
	unsigned long freq, scale_cpu;
	struct em_perf_state *ps;
	int i, cpu;

	/*
	 * In order to predict the performance state, map the utilization of
	 * the most utilized CPU of the performance domain to a requested
	 * frequency, like schedutil.
	 */
	cpu = cpumask_first(to_cpumask(pd->cpus));
	scale_cpu = arch_scale_cpu_capacity(cpu);
	ps = &pd->table[pd->nr_perf_states - 1];
	// 这里将perf_domai计算出来的最大的CPU利用率来推测CPU接下来需要调频的频率
	// 这里可以将freq称为推测频率
	// 计算公式 freq = 1.25 * max_f * max_util / scale_cpu
	// 这里是在最大频率1.25倍进行计算的
	freq = map_util_freq(max_util, ps->frequency, scale_cpu);

	/*
	 * Find the lowest performance state of the Energy Model above the
	 * requested frequency.
	 */
	// 将该频率映射到频率表上
	// 因为freq是在1.5倍最大频率计算的，算出来的推测频率可能大于最大频率
	// 假如大于最大频率的话，for循环执行后ps指向的就是最大频率了
	for (i = 0; i < pd->nr_perf_states; i++) {
		ps = &pd->table[i];
		if (ps->frequency >= freq)
			break;
	}

	/*
	 * The capacity of a CPU in the domain at the performance state (ps)
	 * can be computed as:
	 *
	 *             ps->freq * scale_cpu
	 *   ps->cap = --------------------                          (1)
	 *                 cpu_max_freq
	 *
	 * So, ignoring the costs of idle states (which are not available in
	 * the EM), the energy consumed by this CPU at that performance state
	 * is estimated as:
	 *
	 *             ps->power * cpu_util
	 *   cpu_nrg = --------------------                          (2)
	 *                   ps->cap
	 *
	 * since 'cpu_util / ps->cap' represents its percentage of busy time.
	 *
	 *   NOTE: Although the result of this computation actually is in
	 *         units of power, it can be manipulated as an energy value
	 *         over a scheduling period, since it is assumed to be
	 *         constant during that interval.
	 *
	 * By injecting (1) in (2), 'cpu_nrg' can be re-expressed as a product
	 * of two terms:
	 *
	 *             ps->power * cpu_max_freq   cpu_util
	 *   cpu_nrg = ------------------------ * ---------          (3)
	 *                    ps->freq            scale_cpu
	 *
	 * The first term is static, and is stored in the em_perf_state struct
	 * as 'ps->cost'.
	 *
	 * Since all CPUs of the domain have the same micro-architecture, they
	 * share the same 'ps->cost', and the same CPU capacity. Hence, the
	 * total energy of the domain (which is the simple sum of the energy of
	 * all of its CPUs) can be factorized as:
	 *
	 *            ps->cost * \Sum cpu_util
	 *   pd_nrg = ------------------------                       (4)
	 *                  scale_cpu
	 */
	// 根据推测频率在频点表上对应的cost来算energy
	// 不同频率的cost是常数，在初始化时就已经计算出来
	// 计算cost的时候需要将该perf_domain上的所有util拿出来进行计算
	// 一个perf_domain下的频率是一样的，所以这里计算能耗直接用了sum_util
	return ps->cost * sum_util / scale_cpu;
}

// 寻找工作能耗最低的CPU
static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
{
	unsigned long prev_delta = ULONG_MAX, best_delta = ULONG_MAX;
	struct root_domain *rd = cpu_rq(smp_processor_id())->rd;
	unsigned long cpu_cap, util, base_energy = 0;
	int cpu, best_energy_cpu = prev_cpu;
	struct sched_domain *sd;
	struct perf_domain *pd;

	rcu_read_lock();
	// 从rd取pd的指针
	pd = rcu_dereference(rd->pd);
	if (!pd || READ_ONCE(rd->overutilized))
		goto fail;

	/*
	 * Energy-aware wake-up happens on the lowest sched_domain starting
	 * from sd_asym_cpucapacity spanning over this_cpu and prev_cpu.
	 */
	sd = rcu_dereference(*this_cpu_ptr(&sd_asym_cpucapacity));
	while (sd && !cpumask_test_cpu(prev_cpu, sched_domain_span(sd)))
		sd = sd->parent;
	if (!sd)
		goto fail;

	sync_entity_load_avg(&p->se);
	// p的util为0，直接返回prev_cpu
	if (!task_util_est(p))
		goto unlock;

	// 遍历整个pd链表，计算p在不同pd下的能耗
	for (; pd; pd = pd->next) {
		unsigned long cur_delta, spare_cap, max_spare_cap = 0;
		unsigned long base_energy_pd;
		int max_spare_cap_cpu = -1;

		/* Compute the 'base' energy of the pd, without @p */
		// 计算不包括p的情况下此pd当前的energy
		// 这里传入dst_cpu为-1，计算的就是该perf_domain不包括任务P的util
		// 来进行频率推测，然后用来计算能耗
		base_energy_pd = compute_energy(p, -1, pd);
		// 不包括p的情况下系统的总energy
		base_energy += base_energy_pd;

		// 遍历整个pd中的CPU，计算p放在该CPU上的功耗
		for_each_cpu_and(cpu, perf_domain_span(pd), sched_domain_span(sd)) {
			if (!cpumask_test_cpu(cpu, p->cpus_ptr))
				continue;
			// 计算p放到此CPU后该CPU总共消耗的算力
			util = cpu_util_next(cpu, p, cpu);
			// 这里取的是归一化后的CPU算力
			cpu_cap = capacity_of(cpu);
			spare_cap = cpu_cap;
			// 计算p放到此CPU后剩余的算力
			lsub_positive(&spare_cap, util);

			/*
			 * Skip CPUs that cannot satisfy the capacity request.
			 * IOW, placing the task there would make the CPU
			 * overutilized. Take uclamp into account to see how
			 * much capacity we can get out of the CPU; this is
			 * aligned with schedutil_cpu_util().
			 */
			util = uclamp_rq_util_with(cpu_rq(cpu), util, p);
			// CPU需要保留20%左右的算力，不满足需求后进行下一个CPU的探测
			if (!fits_capacity(util, cpu_cap))
				continue;

			/* Always use prev_cpu as a candidate. */
			// 若对比的这个CPU就是任务之前运行的CPU
			if (cpu == prev_cpu) {
				// 计算p放在该cpu后整个pd的能量消耗
				// 这里传入的dst_cpu为之前p运行的CPU
				// 推测频率是在之前运行CPU进行推测，同时把P的util也计算到了
				prev_delta = compute_energy(p, prev_cpu, pd);
				// 计算p放在该CPU后整个pd增加的能量消耗
				prev_delta -= base_energy_pd;
				// 更新best_delta，取最优能耗
				best_delta = min(best_delta, prev_delta);
			}

			/*
			 * Find the CPU with the maximum spare capacity in
			 * the performance domain
			 */
			// 记录p放上去后剩余算力最大的CPU和最大的剩余算力
			if (spare_cap > max_spare_cap) {
				max_spare_cap = spare_cap;
				max_spare_cap_cpu = cpu;
			}
		}

		/* Evaluate the energy impact of using this CPU. */
		// 同一个簇上的CPU取最大余量算力的那个CPU与其他簇的CPU做能量消耗对比
		if (max_spare_cap_cpu >= 0 && max_spare_cap_cpu != prev_cpu) {
			// 计算p放在算力剩余最大的CPU后整个pd的能量消耗
			// 这里传进去的dst_cpu肯定不会和当前任务p运行的CPU相同
			// 所以在cpu_util_next()中会把p的util加到cpu util上
			cur_delta = compute_energy(p, max_spare_cap_cpu, pd);
			// 计算能量消耗增量
			cur_delta -= base_energy_pd;
			// 如果当前能量增量优于p放在prev_cpu运行的能量消耗，则取该cpu运行p
			if (cur_delta < best_delta) {
				best_delta = cur_delta;
				best_energy_cpu = max_spare_cap_cpu;
			}
		}
	}
unlock:
	rcu_read_unlock();

	/*
	 * Pick the best CPU if prev_cpu cannot be used, or if it saves at
	 * least 6% of the energy used by prev_cpu.
	 */
	// 若prev_cpu找不到，就直接返回最优能耗cpu
	if (prev_delta == ULONG_MAX)
		return best_energy_cpu;

	// 若最优能耗比放在prev_cpu上运行的能耗还要低6.25%以上，则取最优能耗cpu
	if ((prev_delta - best_delta) > ((prev_delta + base_energy) >> 4))
		return best_energy_cpu;

	// 否则不做改变，直接使用prev_cpu运行p
	return prev_cpu;

fail:
	rcu_read_unlock();

	return -1;
}

EAS Mainline

https://git.gitlab.arm.com/linux-arm/linux-power.git

计算 capacity-dmips-mhz

In order to calculate the right capacity-dmips-mhz, the following
test was performed:

  1. CPUFREQ governor was set to ‘performance’ on both clusters
  2. Ran dhrystone with 500000000 iterations for 10 times on each cluster
  3. Calculated the mean result for each cluster
  4. Calculated DMIPS/MHz: dmips_mhz = dmips_per_second / cpu_mhz
  5. Scaled results to 1024:
    result_c0 = dmips_mhz_c0 / dmips_mhz_c1 * 1024
  • CPU调频策略设置为 Performance

D3000M EAS初次测试

测试环境

  • 开发板：D3000M TestA 板
  • 固件版本：BL31: v2.3(release):D3000M-v0.70-p1-8-gaf62092
  • 内核版本：linux v6.6

测试场景

  1. 空闲场景（idle）：即待机场景
  2. 压力测试场景（stress）：stress-ng --cpu <cpu_num> ，使所有CPU占用为100%
  3. 模拟CPU占用场景（load）：lookbusy -c xx，模拟所有CPU占用xx百分比

测试方法

测试分为了三组，分别在上面的测试场景中测量处理器核心平均功耗：

  • no eas: 未开启 EAS 功能
  • eas: 开启 EAS 功能
  • eas modify：将两组cluster中的大小核的 Efficiency Class 设置成一样，小核的Efficiency Class参数为1，大核的Efficiency Class参数为2，开启EAS

通过 /proc/sys/kernel/sched_energy_aware 参数来开启和关闭 EAS 功能进行对比测试。

在对应的测试场景下，使用另一块开发板每隔50ms，通过检流模块分别测量 VDD_BIG1（第二组大核供电）、VDD_BIG0（第一组大核供电）、VDD_M0（第一组小核供电）、VDD_M1（第二组小核供电）的电流，并计算核心瞬时总功耗（并不代表处理器的总功耗，处理器还有其它几路电压，比如VDD_GPU, VDD_DMU未进行测量），每个测试场景测量 10 分钟，将数据进行保存，计算平均功耗。

测试结果

  • 可能是功耗模型不准确，导致开启 EAS 后的功耗，在各个测试场景下会略高于未开启EAS的功耗
  • 修改两组大小核的Efficiency Class为一致后，可以看到功耗会略微提高，印证了之前OS黄少波的说法

测试数据
测试代码