[Android] N版PowerManager powerHint

Posted on 週四 04 八月 2016 in Archive

Power hint顧名思義就是從framework層打hint下去給平台，讓下層知道說現在上面是在謥殺虫(所謂上情下達) 就可以根據情境調整power management的機制(e.g. boost performance, 降freq省電....blahblah) 先來看一下Power HAL有哪些hint:

/*
 * Power hint identifiers passed to (*powerHint)
 */

typedef enum {
    POWER_HINT_VSYNC = 0x00000001,
    POWER_HINT_INTERACTION = 0x00000002,
    /* DO NOT USE POWER_HINT_VIDEO_ENCODE/_DECODE!  They will be removed in
     * KLP.
     */
    POWER_HINT_VIDEO_ENCODE = 0x00000003,
    POWER_HINT_VIDEO_DECODE = 0x00000004,
    POWER_HINT_LOW_POWER = 0x00000005,
    POWER_HINT_SUSTAINED_PERFORMANCE = 0x00000006,
    POWER_HINT_VR_MODE = 0x00000007
} power_hint_t;

最早感覺是為了解決performance issue(VSYNC, INTERACTION, VIDEO) 後來在project volta增加LOW_POWER，讓平台可以安心進入low power mode ~~而不用被譙UX變差~~ 最近N版又多加了SUSTAINED_PERFORMANCE & VR mode VR就顧名思義 Sustained performance指長時間提供穩定performance，避免thermal throttling 目前是讓app可以由Window這個class指示進入這個mode

void setSustainedPerformanceMode(boolean enable)

Related sources:

HAL

hardware/libhardware/include/hardware/power.h

void (*powerHint)(struct power_module *module, power_hint_t hint,
                      void *data);

Framework (frameworks/)

base/core/java/android/os/PowerManagerInternal.java --> 這裡面就看的到囉 base/services/core/java/com/android/server/power/PowerManagerService.java --> java端主要實做

base/services/core/jni/com_android_server_power_PowerManagerService.cpp --> JNI native/services/powermanager/IPowerManager.cpp --> call binder的地方

其中PhoneWindowManager和WindowSurfacePlacer都是透過PowerManagerInternal下power hint的

``` java base/services/core/java/com/android/server/policy/PhoneWindowManager.java mPowerManagerInternal.powerHint(PowerManagerInternal.POWER_HINT_INTERACTION, 0);

``` java base/services/core/java/com/android/server/wm/WindowSurfacePlacer.java
        if (mSustainedPerformanceModeCurrent != mSustainedPerformanceModeEnabled) {
            mSustainedPerformanceModeEnabled = mSustainedPerformanceModeCurrent;
            mService.mPowerManagerInternal.powerHint(
                    mService.mPowerManagerInternal.POWER_HINT_SUSTAINED_PERFORMANCE_MODE,
                    (mSustainedPerformanceModeEnabled ? 1 : 0));
        }

Surface Flinger則是從native層使用

status_t status = mPowerManager->powerHint(POWER_HINT_VSYNC, enabled ? 1 : 0);

[Android PowerManagement]