android的耗電問題，會涉及到wakelock部分。
https://blog.csdn.net/weixin_42322147/article/details/80469590

/*** struct wakeup_source - Representation of wakeup sources** @total_time: Total time this wakeup source has been active.* @max_time: Maximum time this wakeup source has been continuously active.* @last_time: Monotonic clock when the wakeup source's was touched last time.* @prevent_sleep_time: Total time this source has been preventing autosleep.* @event_count: Number of signaled wakeup events.* @active_count: Number of times the wakeup source was activated.* @relax_count: Number of times the wakeup source was deactivated.* @expire_count: Number of times the wakeup source's timeout has expired.* @wakeup_count: Number of times the wakeup source might abort suspend.* @active: Status of the wakeup source.* @has_timeout: The wakeup source has been activated with a timeout.*/ struct wakeup_source {const char *name;struct list_head entry;spinlock_t lock;struct timer_list timer;unsigned long timer_expires;ktime_t total_time; //wakeup source處于active的總時長ktime_t max_time;ktime_t last_time;ktime_t start_prevent_time;ktime_t prevent_sleep_time;unsigned long event_count; unsigned long active_count;unsigned long relax_count;unsigned long expire_count;unsigned long wakeup_count;bool active:1;bool autosleep_enabled:1; };

在root權限下，可以通過查看/d/wakeup_sources來查看wakelock的情況。

name active_count event_count wakeup_count expire_count active_since total_time
max_time last_change prevent_suspend_time
bluetooth_timer 64 64 0 0 0 3213 3001 69776 0

wakeup_sources這個節點的信息對分析耗電比較有用的數據有：
active_count, active_since, total_time。

active_count：上鎖的次數
active_since：當前的wakelock已經持續的時間
total_time：這個鎖開機以來一共lock的時間

上文中active_count=64次
上文中active_since=3213毫秒
上文中total_time=3001毫秒

當CPU無法睡下去時，很可能就是因為某個driver持有wakelock不放導致的。
這時可以從這個節點來分析，找出根源。
不過，這個節點只有root權限才能查看，這是限制條件。

一、 節點的創建
根據節點的名稱，先查看節點生成的文件為kernel/msm-3.18/drivers/base/power/wakeup.c

static int __init wakeup_sources_debugfs_init(void){wakeup_sources_stats_dentry = debugfs_create_file("wakeup_sources",S_IRUGO, NULL, NULL, &wakeup_sources_stats_fops); //創建"/d/wakeup_sources"。return 0; }

二、節點操作的相關函數
static const struct file_operations wakeup_sources_stats_fops = {
.owner = THIS_MODULE,
.open = wakeup_sources_stats_open,
.read = seq_read,
.llseek = seq_lseek,
.release = single_release,
};

三、cat /d/wakeup_sources時調用的函數，wakeup_sources_stats_open

static int wakeup_sources_stats_open(struct inode *inode, struct file *file){return single_open(file, wakeup_sources_stats_show, NULL); }

再看看wakeup_sources_stats_show。

/*** wakeup_sources_stats_show - Print wakeup sources statistics information.* @m: seq_file to print the statistics into.*/ static int wakeup_sources_stats_show(struct seq_file *m, void *unused) {struct wakeup_source *ws;seq_puts(m, "name\t\t\t\t\tactive_count\tevent_count\twakeup_count\t""expire_count\tactive_since\ttotal_time\tmax_time\t""last_change\tprevent_suspend_time\n"); //這就是上面的第一行。rcu_read_lock(); list_for_each_entry_rcu(ws, &wakeup_sources, entry) //互斥遍歷wakeup_sources，每次取出其中之一ws.print_wakeup_source_stats(m, ws); //打印出這個ws的相關信息rcu_read_unlock();return 0; }

再看看print_wakeup_source_stats：

/*** print_wakeup_source_stats - Print wakeup source statistics information.* @m: seq_file to print the statistics into.* @ws: Wakeup source object to print the statistics for.*/ static int print_wakeup_source_stats(struct seq_file *m,struct wakeup_source *ws) {unsigned long flags;ktime_t total_time;ktime_t max_time;unsigned long active_count;ktime_t active_time;ktime_t prevent_sleep_time;int ret;spin_lock_irqsave(&ws->lock, flags);total_time = ws->total_time; //之前的total_timemax_time = ws->max_time;prevent_sleep_time = ws->prevent_sleep_time;active_count = ws->active_count;if (ws->active) { //如果這個wakelock還在，沒有釋放掉ktime_t now = ktime_get();active_time = ktime_sub(now, ws->last_time); //active_time就是開始上鎖到目前時間差total_time = ktime_add(total_time, active_time); // total_time 就是上一次的total_time加上active_timeif (active_time.tv64 > max_time.tv64)max_time = active_time;if (ws->autosleep_enabled)prevent_sleep_time = ktime_add(prevent_sleep_time,ktime_sub(now, ws->start_prevent_time));} else {active_time = ktime_set(0, 0);}ret = seq_printf(m, "%-32s\t%lu\t\t%lu\t\t%lu\t\t%lu\t\t""%lld\t\t%lld\t\t%lld\t\t%lld\t\t%lld\n",ws->name, active_count, ws->event_count,ws->wakeup_count, ws->expire_count,ktime_to_ms(active_time), ktime_to_ms(total_time),ktime_to_ms(max_time), ktime_to_ms(ws->last_time),ktime_to_ms(prevent_sleep_time)); //結果spin_unlock_irqrestore(&ws->lock, flags);return ret; }

四、wakeup_sources，一個當前文件中的全局list。
在init一個wakelock的時候添加。
上面遍歷的 wakeup_sources，本文件中的一個全局鏈表。
很容易猜測到，每次申請一個wake_lock時，都會添加一個item到這個鏈表中。
看看這個全局的list的聲明和初始化。

static LIST_HEAD(wakeup_sources); //初始化。
接下來看這個list的添加。想要使用wakelock，肯定是要先調用下面的init函數。我們在kernel中聲明的wake_lock結構都有wakeup_source結構成員。后面更多的是用這個wakeup_source結構來管理。

static inline void wake_lock_init(struct wake_lock *lock, int type, const char *name) {wakeup_source_init(&lock->ws, name); }

接著看被調用的wakeup_source_init。

static inline void wakeup_source_init(struct wakeup_source *ws, const char *name) {wakeup_source_prepare(ws, name); //準備工作wakeup_source_add(ws); //真正的添加。 }

繼續看wakeup_source_add.

/*** wakeup_source_add - Add given object to the list of wakeup sources.* @ws: Wakeup source object to add to the list.*/ void wakeup_source_add(struct wakeup_source *ws) {unsigned long flags;if (WARN_ON(!ws))return;spin_lock_init(&ws->lock);setup_timer(&ws->timer, pm_wakeup_timer_fn, (unsigned long)ws);ws->active = false; //初始化為非activews->last_time = ktime_get(); //當前時間。spin_lock_irqsave(&events_lock, flags);list_add_rcu(&ws->entry, &wakeup_sources); //添加到wakeup_sourcesspin_unlock_irqrestore(&events_lock, flags); } EXPORT_SYMBOL_GPL(wakeup_source_add);

五、wakelock上鎖時的操作
上鎖時，都會調用下面的wake_lock函數。

static inline void wake_lock(struct wake_lock *lock){__pm_stay_awake(&lock->ws); }

繼續看__pm_stay_awake。

/*** __pm_stay_awake - Notify the PM core of a wakeup event.* @ws: Wakeup source object associated with the source of the event.** It is safe to call this function from interrupt context.*/ void __pm_stay_awake(struct wakeup_source *ws) {unsigned long flags;if (!ws)return;spin_lock_irqsave(&ws->lock, flags);wakeup_source_report_event(ws); //主要函數。del_timer(&ws->timer);ws->timer_expires = 0;spin_unlock_irqrestore(&ws->lock, flags); } EXPORT_SYMBOL_GPL(__pm_stay_awake);

繼續看wakeup_source_report_event。

/*** wakeup_source_report_event - Report wakeup event using the given source.* @ws: Wakeup source to report the event for.*/ static void wakeup_source_report_event(struct wakeup_source *ws) {ws->event_count++; //event_count計數/* This is racy, but the counter is approximate anyway. */if (events_check_enabled)ws->wakeup_count++;//wakeup_count計數if (!ws->active) //如果是非active狀態wakeup_source_activate(ws); //那就變成active }

接著看wakeup_source_activate.

/*** wakup_source_activate - Mark given wakeup source as active.* @ws: Wakeup source to handle.** Update the @ws' statistics and, if @ws has just been activated, notify the PM* core of the event by incrementing the counter of of wakeup events being* processed.*/ static void wakeup_source_activate(struct wakeup_source *ws) {unsigned int cec;/** active wakeup source should bring the system* out of PM_SUSPEND_FREEZE state*/freeze_wake(); //保證上鎖期間CPU不會睡下去ws->active = true;ws->active_count++; //active_count計數ws->last_time = ktime_get(); //這時的時間，也就是開始上鎖的時間if (ws->autosleep_enabled)ws->start_prevent_time = ws->last_time;/* Increment the counter of events in progress. */cec = atomic_inc_return(&combined_event_count);trace_wakeup_source_activate(ws->name, cec); }

六、wakelock釋放時的操作
在kernel wakelock釋放的時候，都會調用下面的wake_unlock函數。

static inline void wake_unlock(struct wake_lock *lock) {__pm_relax(&lock->ws); } 繼續看看__pm_relax。 /*** __pm_relax - Notify the PM core that processing of a wakeup event has ended.* @ws: Wakeup source object associated with the source of the event.** Call this function for wakeup events whose processing started with calling* __pm_stay_awake().** It is safe to call it from interrupt context.*/ void __pm_relax(struct wakeup_source *ws) {unsigned long flags;if (!ws)return;spin_lock_irqsave(&ws->lock, flags);if (ws->active) //如果目前仍是active，那就要釋放掉wakeup_source_deactivate(ws);spin_unlock_irqrestore(&ws->lock, flags); } EXPORT_SYMBOL_GPL(__pm_relax);

再看wakeup_source_deactivate。

/*** wakup_source_deactivate - Mark given wakeup source as inactive.* @ws: Wakeup source to handle.** Update the @ws' statistics and notify the PM core that the wakeup source has* become inactive by decrementing the counter of wakeup events being processed* and incrementing the counter of registered wakeup events.*/ static void wakeup_source_deactivate(struct wakeup_source *ws) {unsigned int cnt, inpr, cec;ktime_t duration;ktime_t now;ws->relax_count++;/** __pm_relax() may be called directly or from a timer function.* If it is called directly right after the timer function has been* started, but before the timer function calls __pm_relax(), it is* possible that __pm_stay_awake() will be called in the meantime and* will set ws->active. Then, ws->active may be cleared immediately* by the __pm_relax() called from the timer function, but in such a* case ws->relax_count will be different from ws->active_count.*/if (ws->relax_count != ws->active_count) {ws->relax_count--;return;}ws->active = false;now = ktime_get();duration = ktime_sub(now, ws->last_time); //完整上鎖的時間ws->total_time = ktime_add(ws->total_time, duration); //這把所從init之后所有上鎖的時間總和if (ktime_to_ns(duration) > ktime_to_ns(ws->max_time))ws->max_time = duration;ws->last_time = now;del_timer(&ws->timer);ws->timer_expires = 0;if (ws->autosleep_enabled)update_prevent_sleep_time(ws, now);/** Increment the counter of registered wakeup events and decrement the* couter of wakeup events in progress simultaneously.*/cec = atomic_add_return(MAX_IN_PROGRESS, &combined_event_count);trace_wakeup_source_deactivate(ws->name, cec);split_counters(&cnt, &inpr);if (!inpr && waitqueue_active(&wakeup_count_wait_queue))wake_up(&wakeup_count_wait_queue); }

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