Drowsy Power Management - University Of Marylandmlentz/papers/drowsy_sosp2015_slides.pdfResume (Thaw...

Drowsy Power Management

Matthew Lentz James Litton Bobby BhattacharjeeUniversity of Maryland

Background Energy Consumption

Fetch Remote Data Communicate with Nearby Device(s) Receive Push Notification Sample Sensor(s) . . .

Mobile devices consume energy without human-interaction

Many (periodic) short-lived events executed:

Power Trace with Events

Power Trace with Events

EventEvent

Event = Pull data from remote server over WiFi

Power Management States

Suspend

Off

On

System in low-power state Memory retains contents

Event

Power Management StatesOnOn

Suspend

Off

On


Event

Suspend

Power Management StatesOnOn

Suspend

Off

On


Event

Suspend

Power Management States

WiFi Controller Power-Save Mode

… …

OnOn

Suspend

Off

On


Event

Suspend

Power Trace with EventsOnOn

EventEvent

What Happens During a Wakeup?


Interrupt (from RTC Alarm)

Suspend→On




Suspend→On Event



Suspend→On Event

Objects held by applications and drivers When all locks released, can enter Suspend

Wakelocks



Suspend→On Event



Suspend→On Event On→Suspend


What Happens During a Wakeup?Acquire wakelockFetch update over WiFiSet future wakeup alarmRelease wakelock



Transitions are InefficientTransitions account for 75% of total energy consumption!



Transitions for Other Events

RTC Alarm (ALM)Bluetooth Connection (BT2)

Push Notification (PSH)Sample Accelerometer (SEN)

85%32%

23%89%


On → Suspend

On → Suspend

Flush filesystem buffers Freeze all tasks Suspend all devices Disable non-boot CPUs Set RAM to self-refresh

1

2

3

4

* Wait for interrupt

5

*

1 2 345

On → Suspend

Flush filesystem buffers Freeze all tasks Suspend all devices Disable non-boot CPUs Set RAM to self-refresh

1

2

3

4

* Wait for interrupt

5

*

1 2 3452 3

2

3

Suspend → On

Suspend → On

Enable CPUs Resume all devices Thaw all tasks

1

2

3

2 31

Suspend → On

Enable CPUs Resume all devices Thaw all tasks

1

2

3

2 31

2

3

2 3


Wake up only what is necessary



{ }Necessary for Pull Data:



{ }Necessary for Pull Data: Alarm Device WiFi Device

System ServicesApplicationa



{ }Necessary for Pull Data: Alarm Device WiFi Device

System ServicesApplicationa

{ }Unnecessary:USB Device

SD Card Device

Calendar App

Bluetooth Device

Power Regulator Devices

Power Regulators

Input Devices

Battery Monitoring Device

…


Construct minimal “wake set” of tasks and devices



Smallest set that maintains correct behavior



Expand on-demand as event progresses



Constraint: No modifications to user-space


Expand on-demand as event progresses


Transitions To/From Drowsy

Suspend

Drowsy

Resume all devices Enable CPUs

3

2

1

Flush filesystem buffers

Disable non-boot CPUs Set RAM to self-refresh

1

2

3

4

5

Freeze all tasks Suspend all devices

Thaw all tasks


Suspend

Drowsy


3

2

1



1

2

3

4

5

3

2


Thaw previously running tasks


Suspend

Drowsy


3

2

1



1

2

3

4

5

3

2



On CPU or Run Queue


Suspend

Drowsy


3

2

1



1

2

3

4

5

3

2


Wake Set = { <Prev. Running Tasks> }



Suspend

Drowsy


3

2

1



1

2

3

4

5

3

2





Suspend

Drowsy


3

2

1



1

2

3

4

5

3

2




Wake Set = { <Prev. Running Tasks>, Task }

Wake Set = { <Prev. Running Tasks>, Task, Device, … }


Suspend

Drowsy


3

2

1



1

2

3

4

5

3

2

2

3

Freeze tasks in wake set Suspend devices in wake set



Wake Set = { <Prev. Running Tasks>, Task }

Wake Set = { <Prev. Running Tasks>, Task, Device, … }

Constructing the Wake Set

Task A

Tim

e

ioctl() command to device

open() named pipe

read() from pipe

Run (I/O)Run (CPU) Run (Device I/O)Task States:

Constructing the Wake SetBlocked

Blocks waiting on condition to be met

Run (I/O)Run (CPU) Run (Device I/O)Task States:

Task A

Tim

e

open() named pipe

read() from pipe

ioctl() command to deviceioctl()


Task B Task A

Satisfies

condition

BlockedRun (I/O)Run (CPU) Run (Device I/O)Task States:

Tim

e

write() to pipe

Blocks waiting on condition to be met

open() named pipe

read() from pipe

Constructing the Wake SetFrozenBlockedRun (I/O)Run (CPU) Run (Device I/O)Task States:

Tim

e

Task B Task A

Suspended


Tim

e

Task B Task A

Suspended

Transition to Suspend (All wakelocks released)


Tim

e

Task B Task A

Suspended

Transition to Suspend (All wakelocks released)

Transition to Drowsy


Wake Set =

{ Task B, Task A }

{ Task B, Task A, Device }

Task B Task A

Tim

e

FrozenBlockedRun (I/O)Run (CPU) Run (Device I/O)Task States:

Suspended


Wake Set =

{ Task B, Task A }

{ Task B, Task A, Device }

Task B Task A

Tim

e

{ Task B }

FrozenBlockedRun (I/O)Run (CPU) Run (Device I/O)Task States:

Suspended

Drowsy Wake Set: Pull Data

IRQ 48

msm-ssbi.0

IRQ 362 IRQ 479

platform rtc-pm8xxx

/dev/alarm AlarmManager ActivityManager

Benchmark

binder

log_main wlan0

PowerManager

pm8921-coremsmgpio rtc0

alarm

wcnss_wlan.0

mpdecision Worker

Compiler

cpu1

cpu2

cpu3

Binder_1 Binder_1 Binder_2

Binder_3

Binder_4

ServerThread

flush-179:0

flush-0:17

Time (ms)

cpu

0 ms 4 ms 6 ms 26 ms 41 ms 91 ms 98 ms13 ms

DeviceTask Wakeup Chained IRQIRQ

Resume(Thaw Running Tasks)

Suspend(Sync Filesystem Buffers)

IRQ 48

msm-ssbi.0

IRQ 362 IRQ 479

platform rtc-pm8xxx


Benchmark

binder

log_main wlan0

PowerManager


alarm

wcnss_wlan.0

mpdecision Worker

Compiler

cpu1

cpu2

cpu3


Binder_3

Binder_4

ServerThread

flush-179:0

flush-0:17

Time (ms)

cpu





Drowsy Wake Set: Pull Data

IRQ 48

msm-ssbi.0

IRQ 362 IRQ 479

platform rtc-pm8xxx


Benchmark

binder

log_main wlan0

PowerManager


alarm

wcnss_wlan.0

mpdecision Worker

Compiler

cpu1

cpu2

cpu3


Binder_3

Binder_4

ServerThread

flush-179:0

flush-0:17

Time (ms)

cpu





IRQ 48

msm-ssbi.0

IRQ 362 IRQ 479

platform rtc-pm8xxx


Benchmark

binder

log_main wlan0

PowerManager


alarm

wcnss_wlan.0

mpdecision Worker

Compiler

cpu1

cpu2

cpu3


Binder_3

Binder_4

ServerThread

flush-179:0

flush-0:17

Time (ms)

cpu





15 tasks thawed & 16 devices resumed

1.8% 1.9%

Implementation

Implemented Drowsy within Android kernel

Platform: Google Nexus 4 (“Mako”)

SLOC: ~4,600

Version: 4.2.2 (Fork of Linux 3.4)

Instrumenting Android

For determining when to add tasks/devices to wake set

Example: file_operations

.open = &drv_open

.read = &drv_read

.write = &drv_write

struct file_operations d_fops:


.open = &drv_open

.read = &drv_read

.write

.write_impl = &drv_write= &drowsy_write



.open = &drv_open

.read = &drv_read

.write

.write_impl = &drv_write= &drowsy_write


int drowsy_write(File *f, …) Device *d = fileToDevice(f) if(d!state == Suspended)

resumeDevice(d)

f!f_ops.write_impl(f, …)

Evaluation: Benchmarking

Handle I/O Event

Acquire Wakelock

Suspend

Release Wakelock

Suspend

Set a future wakeup alarm Accept incoming Bluetooth connection Fetch weather update (and set alarm) Receive incoming push notification Sample the accelerometer (and set alarm)

ALM BT2 PUL PSH SEN

→On →Drowsy

On→ Drowsy→

Evaluation: Measurement

V Pho

neI Ph

one

IPhone = VShunt / RShunt Time

Evaluation: Measurement

V Pho

neI Ph

one

V Pho

toIPhone = VShunt / RShunt Time

Evaluation: MeasurementLED Toggled On

(Software Timestamp)

V Pho

neI Ph

one

V Pho

toIPhone = VShunt / RShunt Time

Improvement: Wakeup Events (1 Core, Powersave)

Plus (1 Core, Powersave) Plus

Improvement: Wakeup Events

Drowsy is 1.5-5x as energy efficient

(1 Core, Powersave) Plus (1 Core, Powersave) Plus

Improvement: Wakeup Events

cpuidle entered deep idle states more often

in the Drowsy state

Drowsy is 1.5-5x as energy efficient

(1 Core, Powersave) Plus (1 Core, Powersave) Plus

Improvement: Wakeup Events (1 Core, Powersave)

Plus (1 Core, Powersave) Plus

Wakeup Cycle: Pull DataAndroid Event

Suspend→OnOn→Suspend

Drowsy Event & Wake Set

Suspend

Drowsy

→

Drowsy

Suspend

→

Wakeup Cycle: Pull DataAndroid Event


Drowsy Event & Wake Set

Suspend

Drowsy

→

Drowsy

Suspend

→

Wakeup Cycle: Pull DataAndroid

WiFi Tail Energy

Event


Improvement: Battery Life


Converges to 0% as the interval increases


Converges to 0% as the interval increases

Benefits of Drowsy aggregate across all

applications on device

Summary

Source code is available at:

www.cs.umd.edu/projects/drowsy/

Drowsy wakes up the minimal set of tasks and devicesis 1.5 - 5x as energy efficient for short-lived events

Existing power management not optimized for short-lived events

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