Ghosts in the Machine: Interfaces for Better Power Management
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![Page 1: Ghosts in the Machine: Interfaces for Better Power Management](https://reader034.fdocuments.in/reader034/viewer/2022051416/56812c25550346895d90903c/html5/thumbnails/1.jpg)
Ghosts in the Machine:Interfaces for Better Power Management
Manish Anand
Edmund B. Nightingale
Jason Flinn
Electrical Engineering and Computer Science Dept.University of Michigan
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Manish Anand
2
Need for improved power management
Capabilities of mobile handheld devices improving rapidly: Wireless connectivity Storage capacity
Battery capacity improving slowly I/O devices decrease handheld battery lifetime by 60% OEMs provide techniques to reduce battery consumption by
severely compromising the performance Careful power management needed
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Tradeoff between energy and performance
Inherent tradeoff exists between performance and energy conservation
Goals of power management involve:
Lower energy usage
Lower interactive response time (performance)
Time
En
erg
y
Good performance
Extended battery life
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Current device power management
better performance and energy conservation
simplicityMODULARITY
moreless
Problem: Device-centric strategies do not consider the operating environment contexts, such as Base power of mobile computer Activity of other devices Application intent
Our Approach: Provide an infrastructure to expose additional information about operating environment to both applications and devices
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Goals and contributions
Goals: Improve both performance and energy Enable cross-device optimization Allow end users to specify their relative priorities for
performance and energy conservation
Contributions: Simple interfaces to expose additional contexts Power manager for querying device state Self-tuning power management (STPM) modules for disk, n/w Ghost hints for cross-device power management
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Outline Motivation and background Overview of our solution Interfaces for better power management Adaptive caching Evaluation Related work and conclusions
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Review: power management Network Device: 802.11b wireless
CAM – Continuously Active Mode PSM – Power Saving Mode
+ power usage reduced by 70 to 80%
- delay proportional to polling period (100 ms)
Disk Device: IBM/Hitachi microdrive Active Low Power Idle / Standby
+ power usage reduced by 55% / 90%
- transition time of 300ms / 800ms
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Impact of power management
Assumption: Fetching data from local storage is less costly
Web Fetch Time
0
500
1000
1500
2000
2500
0 100 200 300 400 500 600
File Size (KB)
Fet
ch t
ime
(ms)
Disk Standby
Disk Active
Network PSM
Network CAM
Local data access could be more expensive for small files Break-even point is dependent on the state of the device Simple adaptation through cache hierarchy
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Limitation of adaptation
Example: Browser fetching many small images For single image fetching from network is correct For many images fetching from disk is correct
Amortized transition cost over many reads
Problem: Reactive adaptive caching does not help Disk continues to be in standby state
Solution: Apps disclose “accesses that might have been” We use ghost hints to implement this
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Manish Anand
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Outline Motivation and background Overview of our solution Interfaces for better power management Adaptive caching Evaluation Related work and conclusions
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Energy-aware architecture
Applications
Power Manager
NetworkHints
DeviceCharacteristics & Current State
STPMNetwork
STPMDisk
ModeTransitions
ModeTransitions
Cache Manager
Ghost HintsGhost Hints
Data AccessDecision
Notify NetworkState Change
Notify DiskState Change
Operating System
Disk Device Driver
Network Device Driver
MobiCom ‘03
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Power manager Central repository that maintains information about:
State of the device Performance characteristics of I/O devices Energy characteristics of I/O devices
Power manager interface 3 calls for devices – register, deregister and notify 5 calls for applications – 4 to query device state and
characteristics, 1 for registering callbacks
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Self-tuning power management STPM modules consider:
Application access patterns Base power of mobile computer Energy and performance characteristics of the device Relative priority of performance and energy conservation
STPM modules decide: Time to transition to high power state Time to transition to low power state
Energy conservation
Performance0 100knob
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Disk power management with STPM
Transition to power saving mode employs Break-even heuristic
Disk is likely to remain idle if it has been idle for a period Incorporate the STPM principles
Transition to active mode employs both Reactive strategy
Transition on a request Proactive strategy
Use ghost hints to transition even with no device access
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Ghost hints
Ghost Hint Ghost Hint
Expended Energy between hints
Break-even Threshold
Ghost hints contain opportunity cost in terms of time and energy Issued by the application, when a poor I/O path is chosen due to inappropriate device state
Decrements energy cost of being active between hints Transitions to high performance state on an overflow
state change on overflow
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Cache manager
Keeps the meta-data information in-memory hash table Determines the weighted cost of going to network or disk Maintains a write queue and delays writes to the disk
ApplicationsCache
Manager
Disk
CacheStatus?
network bettern/w fetch
data PutData
flush
ghost hint
STPMModule
PowerManagerdevice state
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Outline Motivation and background Overview of our solution Interfaces for better power management Adaptive caching Evaluation Related work and conclusions
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Evaluation Goals:
Effect of cache manager’s adaptive, cross-device strategy
Influence of global knob
Benefits of ghost hints
Client: iPAQ handheld with Cisco 350 wireless card and IBM/Hitachi microdrive
Test applications:
Email-sync - recorded e-mail activity
Dillo web browser with wwwoffle - Berkeley web traces
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Effectiveness of energy-aware caching
0
100
200
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500
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Average Response Time
(ms)
E-mail Web
Static
Adaptive
0
500
1000
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Energy (Joules)
E-mail Web
Equal priority for performance and energy Average response time is reduced by 27% to 42% Total energy usage is reduced by 5% to 9%
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E-mail and web with no ghost hints
STPM modules base their decision solely on device accesses No change for knob value less than 95
k=100
k=99
k=95-0 static
2000
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3000
3500
4000
4500
5000
0 200 400 600
Average Response Time(ms)
En
erg
y(J
)
k=100
k=99
k=95-0static
120014001600
1800200022002400
260028003000
0 200 400 600
Average Response Time(ms)
En
erg
y(J
)
E-mail Web
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Importance of ghost hints
Email: Substantial benefit when performance is high priority Web: Less likely to see run of accesses clustered together
k=100
k=99
k=95k=90-0
k=99
k=95-0 static
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0 200 400 600
Average Response Time(ms)
En
erg
y(J
)
k=100
k=99
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k=70-0k=90
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k=95-0static
1200140016001800200022002400260028003000
0 200 400 600
Average Response Time(ms)
En
erg
y(J
)
E-mail Web
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Importance of ghost hints
static
knob=50-0knob=70knob=90
knob=95
knob=99
knob=95-0
knob=99
knob=100
2000
2500
3000
3500
4000
4500
5000
0 200 400 600
Average Response Time(ms)
En
erg
y(J)
Web with full cache
Ghost hints show a positive effect on the system
Ghost hints yield substantial benefit for some workloads, and do no harm in the situations where they seem ineffective
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Related work We are the first system to efficiently access data on multiple I/O
Burstiness for energy efficiency (Weissel ’02, Papathanasiou ’03, Heath ‘02)
ACPI: similar to power manager but too complex, does not disclose device characteristics
Wake on Wireless (Shih ’02)
OS level power management (ECOSystem, Odyssey)
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Conclusions
Contributions: Improved power management interfaces: Power manager for querying device state STPM modules for disk, network Ghost hints for cross-device power management
Current work: Modification of cached data Multiple network and storage devices Feedback loop to dynamically set the global knob
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Ghosts in the Machine:Interfaces for Better Power Management
Manish Anand
Edmund B. Nightingale
Jason Flinn
Electrical Engineering and Computer Science Dept.University of Michigan
![Page 26: Ghosts in the Machine: Interfaces for Better Power Management](https://reader034.fdocuments.in/reader034/viewer/2022051416/56812c25550346895d90903c/html5/thumbnails/26.jpg)
Manish Anand
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Dynamic Power Management
The energy used by the I/O devices can be prohibitive, without power managementHitachi Microdrive Cisco 350 wireless card
Mode Power Mode Power
Performance Idle 760 mW CAM 1410 mW
Low-Power Idle 340 mW PSM 390 mW
Standby 80 mW
Battery lifetime is decreased by 60% without power management
Drawback of using power management Network device
Delay proportional to the polling period Disk device
Transition cost to switch to active mode (300ms to 800ms)
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ghostrealized disk spin-up
PSMswitch
CAMswitch
Network access Disk access
ghost hints STPM disk hints
STPM network hints
Applications
Disk
Network
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Network Power Management with STPM
STPM network switches from PSM to CAM when: Application specifies max delay < beacon period Disclosed transfer size > break-even size Many forthcoming transfers are likely
To predict forthcoming transfers STPM network generates an empirical distribution of run lengths
>150 ms >150 ms>150 ms
Transfers
Run Run Run Run