linux核心3.4基於wakeup_source的autosleep機制分析
阿新 • • 發佈：2018-12-31
一：wakeup_source簡介：
linux 3.4核心PM使用了wakeup_source來保持喚醒狀態，也就是keep awake。之前android一直是基於Linux加入了wake_lock機制來阻止系統休眠，後來Linux 3.4核心加入了wakeup_source來管理，安卓4.4跟著升級核心也就摒棄了自己的臃腫的wake_lock機制，在對上層介面並不改變，在核心wake_lock實現直接基於wakeup_source來實現的。當然也會帶來debug上的一些問題，比如以前的wake_lock自身帶有強大的debug資訊，那麼我們在除錯的時候可以自己看見dmesg中預設列印active wake lock XXX，很直觀來辨別需要休眠的時候那個wake lock有問題阻止了休眠。這個需要我們自己來完善。個人認為改進很大，現在使用了autosleep機制，只要不存在任何active wakeup_source了，系統自動休眠，當有active wake_source自動block住，個人認為休眠更及時，非休眠時間在減少，同時不會消耗額外的資源。使用基於queue work與程序block來管理suspend。還有這裡的wakeup_source個人覺得應該叫keepawake_source或者stayawake_souce，畢竟系統的喚醒也就是cpu的再次執行是由中斷喚醒的而不是wakeup_source。同時安卓4.4還有一個重大改變就是去除了early suspend機制改為fb event通知機制。那麼現在就只有suspend與resume,runtime suspend與runtime resume了。/**
* 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 sorce was activated.
* @relax_count: Number of times the wakeup sorce 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;
struct list_head list;
spinlock_t lock;
struct timer_list timer;
unsigned long timer_expires; //超時時間，也就是wake_lock_timeout()裡面的時間引數，超時後會執行deactivate函式
ktime_t total_time;
ktime_t max_time;
ktime_t last_time;
ktime_t start_prevent_time;
ktime_t prevent_sleep_time;
unsigned long event_count; //event計數
unsigned long active_count;//active計數
unsigned long relax_count;
unsigned long expire_count;
unsigned long wakeup_count;
bool active:1; //用於判斷是否是active狀態
bool autosleep_enabled:1;//這個變數是來標記active等時間的
};
//active任何wakeup_source都會執行該函式，標記active為true
/**
* 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;
ws->active = true;
ws->active_count++;
ws->last_time = ktime_get();
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);
}
//deactivate任何wakeup_source都會執行該函式，標記active為false
/**
* 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);
ws->total_time = ktime_add(ws->total_time, duration);
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); //當不存在任何active wake_up source的時候喚醒try_to_suspend程序。
}
}
wakup_source的申請與釋放：
1：使用安卓的wake_lock介面：wake_lock（），wake_lock_timeout（）,wake_unlock（）;
2: 使用wakeup_source自帶的介面：pm_stay_awake（）,pm_relax();這裡的name就是device name。
二：autosleep分析：
sys介面：sys/power/autosleep
亮屏時libsuspend會寫入off,滅屏寫入mem
static ssize_t autosleep_show(struct kobject *kobj,
struct kobj_attribute *attr,
char *buf)
{
suspend_state_t state = pm_autosleep_state();
if (state == PM_SUSPEND_ON)
return sprintf(buf, "off\n");
#ifdef CONFIG_SUSPEND
if (state < PM_SUSPEND_MAX)
return sprintf(buf, "%s\n", valid_state(state) ?
pm_states[state] : "error");
#endif
#ifdef CONFIG_HIBERNATION
return sprintf(buf, "disk\n");
#else
return sprintf(buf, "error");
#endif
}
static ssize_t autosleep_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t n)
{
suspend_state_t state = decode_state(buf, n);
int error;
if (state == PM_SUSPEND_ON
&& strcmp(buf, "off") && strcmp(buf, "off\n"))
return -EINVAL;
error = pm_autosleep_set_state(state);
return error ? error : n;
}
power_attr(autosleep);
int pm_autosleep_set_state(suspend_state_t state)
{
#ifndef CONFIG_HIBERNATION
if (state >= PM_SUSPEND_MAX)
return -EINVAL;
#endif
__pm_stay_awake(autosleep_ws); //防止系統休眠
mutex_lock(&autosleep_lock);
autosleep_state = state;
__pm_relax(autosleep_ws); //釋放上面的wake up source
if (state > PM_SUSPEND_ON) {
pm_wakep_autosleep_enabled(true); //設定所有wake up source裡面的autosleep_enabled為真，這個變數不會對休眠有影響，但是會標記active的時間,使用debugfs可以看見
queue_up_suspend_work();//排程工作佇列，會執行try_to_suspend（），其實state mem執行try_to_suspend（），一次就可以了，後面再分析。
} else {
pm_wakep_autosleep_enabled(false);//設定所有wake up source裡面的autosleep_enabled為假
}
mutex_unlock(&autosleep_lock);
return 0;
}
重頭戲：try_to_suspend
static void try_to_suspend(struct work_struct *work)
{
unsigned int initial_count, final_count;
if (!pm_get_wakeup_count(&initial_count, true)) //獲取initial_count，這個函式會block住，當存在active wakeup source的時候，直到wakeup source為detative狀態
goto out;
mutex_lock(&autosleep_lock);
if (!pm_save_wakeup_count(initial_count)) {//儲存initial_count，不會block，當然也會檢查是否有active wakeup source，當有active存在再次queue work。
mutex_unlock(&autosleep_lock);
goto out;
}
if (autosleep_state == PM_SUSPEND_ON) {//當為ON狀態時，return。//在睡眠期間跟了很久沒有遇見過這種情況
mutex_unlock(&autosleep_lock);
return;
}
if (autosleep_state >= PM_SUSPEND_MAX)
hibernate(); //hibernate高通平臺目前不支援
else
pm_suspend(autosleep_state); //進入pm_suspend，dmesg會有PM: suspend entry 與PM: suspend exit來標記，這裡面會執行freeze task,suspend與resume，disable cpu的操作。核心PM最重要的函式。
mutex_unlock(&autosleep_lock);
if (!pm_get_wakeup_count(&final_count, false))//獲取final_count，非block,當然也會檢查是否有active wakeup source，當有active存在再次queue work
goto out;
/*
* If the wakeup occured for an unknown reason, wait to prevent the
* system from trying to suspend and waking up in a tight loop.
*/
if (final_count == initial_count) //這裡遇見未知原因，initial_count與final_count相等，超時500ms後繼續往下執行。這種現象我也是跟了許久沒有遇見過。
schedule_timeout_uninterruptible(HZ / 2);
out:
queue_up_suspend_work(); //排程queue work會再次執行該函式，實際上只要一次echo mem > sys/power/autosleep後這個程序一直會在auto_sleep cycle。
}
pm_get_wakeup_count原型,個人感覺這個是仿__wait_event_interruptible（）而寫的。
bool pm_get_wakeup_count(unsigned int *count, bool block)
{
unsigned int cnt, inpr;
if (block) { //當block為真時，該程序可能會block住
DEFINE_WAIT(wait);
for (;;) {
prepare_to_wait(&wakeup_count_wait_queue, &wait,
TASK_INTERRUPTIBLE);
split_counters(&cnt, &inpr); //有active的wakeup_source存在就是block住，否則block
if (inpr == 0 || signal_pending(current))
break;
schedule();//在這裡面block住，直到最後一個active的wakeup_source deactivate時會喚醒該程序，之後會break出來。
}
finish_wait(&wakeup_count_wait_queue, &wait);
}
split_counters(&cnt, &inpr);
*count = cnt;
return !inpr;
}
那麼有2個問題，按power鍵喚醒系統是退出try_to_suspend了嗎？
首先系統是如何被喚醒的？這個是由硬體中斷喚醒的，比如我們這裡的power鍵，還有其他的比如alarm等其他硬體中斷，只要我們在中斷申請時enbale_irq_wake（），那麼睡眠期間，只要觸發該中斷就可以喚醒系統。那麼在try_to_suspend裡面喚醒後pm_suspend（）執行完resume後會退出來，接著會獲取final_count，在這裡是存在active wake_up source的（在out之前加添的列印active wakeup_source，下面的dmesg證明了存在的wakeup_source），之後執行out,後排程工作佇列，再次進入try_to_suspend（），在第一次獲取initial_count後便會遇見active wakeup_source，這裡面更多的是系統上層加的wakeup_source，那麼try_to_suspend()會一直block在pm_get_wakeup_count()裡面直到滅屏和所有wakeup_source deactivate時會再次進入pm_suspend（）休眠。
這裡也就解釋了為什麼只要執行一次ehco mem > sys/power/autosleep後自動可以休眠了的原因。
看下面的dmesg:
<6>[ 928.536418] CPU0: msm_cpu_pm_enter_sleep mode 000000,00000000,00000000,00000000,00000000,00000020,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000
<6>[ 928.543066] PM: noirq resume of devices complete after 6.020 msecs
<6>[ 928.548512] PM: early resume of devices complete after 2.598 msecs
<6>[ 928.650793] PM: resume of devices complete after 102.266 msecs
<6>[ 928.660290] Restarting tasks ... done.
<6>[ 928.681208] PM: suspend exit 1970-01-05 05:23:32.206389881 UTC
<6>[ 928.681229] active wake lock KeyEvents
<6>[ 928.681267] active wake lock qpnp_soc_wake
<6>[ 928.681284] active wake lock alarm, time left 486
<6>[ 928.681342] active wake lock KeyEvents
<6>[ 928.681584] active wake lock qpnp_soc_wake
<6>[ 928.681600] active wake lock alarm, time left 486
<6>[ 928.696345] request_suspend_state: wakeup at 928691792356 (1970-01-05 05:23:32.221521704 UTC)
<6>[ 928.708608] mdss_dsi_panel_power on=1
還有一個與wakeup source無關的問題,為什麼suspend後就一直停留在那裡不動了？
這個是cpu停止運轉了，下面再分析下程式碼。
核心函式suspend_devices_and_enter（）：
/**
* suspend_devices_and_enter - Suspend devices and enter system sleep state.
* @state: System sleep state to enter.
*/
int suspend_devices_and_enter(suspend_state_t state)
{
int error;
bool wakeup = false;
if (!suspend_ops)
return -ENOSYS;
trace_machine_suspend(state);
if (suspend_ops->begin) {
error = suspend_ops->begin(state);
if (error)
goto Close;
}
suspend_console();
suspend_test_start();
error = dpm_suspend_start(PMSG_SUSPEND);//這裡會執行所有driver的suspend函式，suspend裡面有active wakeup_source或者return 為真的話，suspend會報錯
if (error) {
printk(KERN_ERR "PM: Some devices failed to suspend\n");
goto Recover_platform;
}
suspend_test_finish("suspend devices");
if (suspend_test(TEST_DEVICES))
goto Recover_platform;
do {
error = suspend_enter(state, &wakeup);//這裡會diable cpu
} while (!error && !wakeup
&& suspend_ops->suspend_again && suspend_ops->suspend_again());
Resume_devices:
suspend_test_start();
dpm_resume_end(PMSG_RESUME);
suspend_test_finish("resume devices");
resume_console();
Close:
if (suspend_ops->end)
suspend_ops->end();
trace_machine_suspend(PWR_EVENT_EXIT);
return error;
Recover_platform:
if (suspend_ops->recover)
suspend_ops->recover();
goto Resume_devices;
}
static int suspend_enter(suspend_state_t state, bool *wakeup)
{
int error;
if (suspend_ops->prepare) {
error = suspend_ops->prepare();
if (error)
goto Platform_finish;
}
error = dpm_suspend_end(PMSG_SUSPEND);
if (error) {
printk(KERN_ERR "PM: Some devices failed to power down\n");
goto Platform_finish;
}
if (suspend_ops->prepare_late) {
error = suspend_ops->prepare_late();
if (error)
goto Platform_wake;
}
if (suspend_test(TEST_PLATFORM))
goto Platform_wake;
error = disable_nonboot_cpus(); //disable nonboot cpu注意還有cpu需要下面disable的
if (error || suspend_test(TEST_CPUS))
goto Enable_cpus;
arch_suspend_disable_irqs();
BUG_ON(!irqs_disabled());
error = syscore_suspend();
if (!error) {
*wakeup = pm_wakeup_pending();
if (!(suspend_test(TEST_CORE) || *wakeup)) {
error = suspend_ops->enter(state); //在這裡cpu會停止執行，直到中斷喚醒
//下面的全部是喚醒的操作了
events_check_enabled = false;
}
syscore_resume();
}
arch_suspend_enable_irqs();
BUG_ON(irqs_disabled());
Enable_cpus:
enable_nonboot_cpus();
Platform_wake:
if (suspend_ops->wake)
suspend_ops->wake();
dpm_resume_start(PMSG_RESUME);
Platform_finish:
if (suspend_ops->finish)
suspend_ops->finish();
return error;
}
平臺賦值，這裡debug平臺是基於msm8974的：
static const struct platform_suspend_ops lpm_suspend_ops = {
.enter = lpm_suspend_enter,//在這裡面disbale cpu，停止執行程式
.valid = suspend_valid_only_mem,
.prepare_late = lpm_suspend_prepare,
.wake = lpm_suspend_wake,
};
新增顯示wake_lock的dmesg:
<6>[ 90.964850] CPU0: msm_cpu_pm_enter_sleep mode 000000,00000000,00000000,00000000,00000000,00000020,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000
<6>[ 90.965302] Enabling non-boot CPUs ...
<6>[ 90.968303] CPU3 is up
<6>[ 90.970699] PM: noirq resume of devices complete after 2.382 msecs
<6>[ 90.973460] PM: early resume of devices complete after 1.443 msecs
<6>[ 91.097369] PM: resume of devices complete after 123.888 msecs
<6>[ 91.112858] Restarting tasks ... done.
<6>[ 91.141699] PM: suspend exit 1970-01-05 03:59:28.158266979 UTC
<6>[ 91.141776] PM: suspend entry 1970-01-05 03:59:28.158347917 UTC
<6>[ 91.141801] PM: Syncing filesystems ... done.
<6>[ 91.222299] Freezing user space processes ... (elapsed 0.03 seconds) done.
<6>[ 91.258126] Freezing remaining freezable tasks ... (elapsed 0.02 seconds) done.
<6>[ 91.278279] Suspending console(s) (use no_console_suspend to debug)
<6>[ 91.384933] PM: suspend of devices complete after 95.062 msecs
<6>[ 91.397910] PM: late suspend of devices complete after 12.934 msecs
<6>[ 91.413019] PM: noirq suspend of devices complete after 15.064 msecs
<6>[ 91.413059] Disabling non-boot CPUs ...
<6>[ 91.424477] CPU0: msm_cpu_pm_enter_sleep mode 000000,00000000,00000000,00000000,00000000,00000020,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000//這裡cpu停止執行直到中斷喚醒
<6>[ 91.425144] Enabling non-boot CPUs ...
<6>[ 91.432354] CPU3 is up
<6>[ 91.444416] PM: noirq resume of devices complete after 11.997 msecs
<6>[ 91.460948] PM: early resume of devices complete after 10.458 msecs
<6>[ 91.577213] PM: resume of devices complete after 116.231 msecs
<6>[ 91.584876] Restarting tasks ... done.
<6>[ 91.614571] PM: suspend exit 1970-01-05 03:59:35.550203849 UTC
<6>[ 91.614639] active wake lock rmt_storage_-1220268312
<6>[ 91.689912] PM: suspend entry 1970-01-05 03:59:35.625550620 UTC
<6>[ 91.689921] PM: Syncing filesystems ... done.
<6>[ 91.700706] Freezing user space processes ...
<3>[ 91.712870] Freezing of user space aborted
<6>[ 91.712898]
<6>[ 91.712903] Restarting tasks ... done.
<6>[ 91.720540] PM: suspend exit 1970-01-05 03:59:35.656175256 UTC
<6>[ 91.720574] PM: suspend entry 1970-01-05 03:59:35.656214579 UTC
<6>[ 91.720586] PM: Syncing filesystems ... done.
<6>[ 91.801097] Freezing user space processes ...
<3>[ 91.815050] Freezing of user space aborted
<6>[ 91.815075]
<6>[ 91.815083] Restarting tasks ... done.
<6>[ 91.823603] PM: suspend exit 1970-01-05 03:59:35.759241558 UTC
<6>[ 91.823633] PM: suspend entry 1970-01-05 03:59:35.759272964 UTC
<6>[ 91.823643] PM: Syncing filesystems ... done.
<6>[ 91.911985] Freezing user space processes ... (elapsed 0.03 seconds) done.
<6>[ 91.949378] Freezing remaining freezable tasks ... (elapsed 0.01 seconds) done.
<6>[ 91.969089] Suspending console(s) (use no_console_suspend to debug)
<6>[ 92.085594] PM: suspend of devices complete after 98.499 msecs
<6>[ 92.098615] PM: late suspend of devices complete after 12.975 msecs
<6>[ 92.113909] PM: noirq suspend of devices complete after 15.249 msecs
<6>[ 92.113951] Disabling non-boot CPUs ...
<6>[ 92.147320] CPU0: msm_cpu_pm_enter_sleep mode 000000,00000000,00000000,00000000,00000000,00000020,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000
<6>[ 92.148265] Enabling non-boot CPUs ...
<6>[ 92.155121] CPU1 is up
<6>[ 92.163797] CPU2 is up
<6>[ 92.174144] CPU3 is up
<6>[ 92.186556] PM: noirq resume of devices complete after 12.344 msecs
<6>[ 92.199945] PM: early resume of devices complete after 10.020 msecs
<6>[ 92.317528] PM: resume of devices complete after 117.548 msecs
<6>[ 92.326254] Restarting tasks ... done.
<6>[ 92.342025] PM: suspend exit 1970-01-05 04:00:48.122436614 UTC
<6>[ 92.342337] active wake lock qpnp-vadc-f611ac00
<6>[ 92.342357] active wake lock alarm, time left 481
<6>[ 92.411428] PM: suspend entry 1970-01-05 04:00:48.191838905 UTC
<6>[ 92.411451] PM: Syncing filesystems ... done.
<6>[ 92.419086] Freezing user space processes ...
<3>[ 92.431173] Freezing of user space aborted
<6>[ 92.431213]
<6>[ 92.431225] Restarting tasks ... done.
<6>[ 92.441575] PM: suspend exit 1970-01-05 04:00:48.221987864 UTC
<6>[ 92.441709] active wake lock qpnp-vadc-f611ac00
<6>[ 92.445004] PM: suspend entry 1970-01-05 04:00:48.225417551 UTC
<6>[ 92.445026] PM: Syncing filesystems ... done.
<6>[ 92.525764] Freezing user space processes ...
<3>[ 92.541465] Freezing of user space aborted
<6>[ 92.541523]
<6>[ 92.541545] Restarting tasks ... done.
<6>[ 92.558768] PM: suspend exit 1970-01-05 04:00:48.339166145 UTC
<6>[ 92.558865] PM: suspend entry 1970-01-05 04:00:48.339268645 UTC
<6>[ 92.558898] PM: Syncing filesystems ... done.
<6>[ 92.656122] Freezing user space processes ... (elapsed 0.04 seconds) done.
<6>[ 92.699091] Freezing remaining freezable tasks ... (elapsed 0.01 seconds) done.
<6>[ 92.718891] Suspending console(s) (use no_console_suspend to debug)
<6>[ 92.832084] PM: suspend of devices complete after 97.905 msecs
<6>[ 92.845099] PM: late suspend of devices complete after 12.971 msecs
<6>[ 92.860407] PM: noirq suspend of devices complete after 15.264 msecs
<6>[ 92.860447] Disabling non-boot CPUs ...
<6>[ 92.895114] CPU0: msm_cpu_pm_enter_sleep mode 000000,00000000,00000000,00000000,00000000,00000020,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000