Yukta: Multilayer Resource Controllers to Maximize...
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Yukta: Multilayer Resource Controllers to Maximize Efficiency
Raghavendra Pradyumna Pothukuchi Sweta Yamini Pothukuchi
Petros Voulgaris Josep Torrellas
International Symposium on Computer Architecture (ISCA) 2018
http://iacoma.cs.uiuc.edu/
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Resource Management in Computers
Limited resources Many objectives
Configurable parameters
Energy Storage
Frequency Scheduling
Performance Thermals Fairness
Resource Management System
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Designing Computer Resource Management Systems
Hardware
OS/Runtime
Application
Different resources, parameters and design teams!
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Modular Coordinated Handle uncertainty
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Contributions of This Work
▪ Propose Robust Control Theory for computer resource management – Describe why robust control theory is essential for computers
▪ Develop Yukta, a modular approach for coordinated multilayer control – Present how robust control theory is applied to multilayer resource management
▪ Prototype Yukta on an ARM big.LITTLE octacore running Ubuntu – 37% better performance and 20% lower energy than state-of-the-art
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Why Robust Control Theory is Suitable for Computers? - I
▪ Robust control theory: Branch of control theory for uncertain environments
▪ Designers set a guardband for the amount of uncertainty to tolerate – 60% guardband ⇒ controller’s guarantees hold even if model is off by 60%
▪ Computer control faces many forms of uncertainty – Partial system view, controller interference, program behavior, limited modeling…
System
Uncertainty Model
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Robustness to uncertainty enables optimality under modularity
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▪ Robust controllers have input channels for communication
Conventional Controller
Why Robust Control Theory is Suitable for Computers? - II
System (Processor)
Outputs Inputs Robust Controller
_ + Targets
External signals #Tasks (from OS)
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e.g., frequency e.g., power
We use Externals signals for controller communication
e.g., power target
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Why Robust Control Theory is Suitable for Computers? - III
▪ Can work with discretized inputs as common in computers – E.g., core frequency, 𝑓∈{2 𝐺𝐻𝑧, 2.2 𝐺𝐻𝑧 …3 𝐺𝐻𝑧}
▪ Guarantee precise bounds on meeting targets – E.g., core power can be kept within ±0.05 W of the power target
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Robust control theory is highly desirable for computer systems
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e.g., power target
Multilayer system
Robust Controller
Yukta: Multilayer Robust Controllers
Modularly designed and guaranteed optimal behavior
First to propose robust control for modular multilayer management
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Layer 1 (Processor)
Outputs Inputs _ + Targets
External signals #Tasks (from OS)
e.g., frequency e.g., power
Robust Controller
Layer 2 (OS)
Outputs Inputs _ +
Targets Optimizer
Optimizer
Design goals
min E×D
min E×D
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Automated Synthesis of the Robust Controller ▪ Designer provides a model, and: – Output deviation bounds (𝐵) : e.g, ±0.05W for power deviations
– Input weights (𝑊) : Relative overheads
– Discrete input values (Δ↓in ) – Uncertainty guardbands ( Δ↓𝑢 ) : Degree of desired robustness
Model Observed Outputs
Inputs Robust
Controller _ + Targets
𝚫↓𝒊𝒏 𝚫↓𝒖 𝑩 𝑾
Deviations
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Nominal loop
System
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Automated Synthesis of the Robust Controller ▪ Designer provides a model, and: – Output deviation bounds (𝐵) : e.g, ±0.05W for power deviations
– Input weights (𝑊) : Relative overheads
– Discrete input values (Δ↓in ) – Uncertainty guardbands ( Δ↓𝑢 ) : Degree of desired robustness
Nominal loop 𝑵
𝚫
Targets Observed Outputs
Structured Singular Value 𝑺𝑺𝑽(𝑵,𝚫)
Can the controller guarantee the bounds optimally even under uncertainty as big as the guardband?
Synthesis is automated!
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Designing Multilayer Controllers
Select inputs, outputs
Decide external signals
Set controller
parameters
Design controller
Modular and practical design
Obtain model
Select inputs, outputs
Decide external signals
Set controllers
parameters
Design controller
Obtain model
Interface
Layer 1, e.g. OS team
Layer 2, e.g. Hardware team
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Prototype Yukta on a Challenging System
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Minimize Energy×Delay under thermal and power constraints
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Prototyped Yukta Architecture
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Designing Robust Controllers for the Prototype
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Select inputs, outputs
Decide External signals
Set controller
parameters
Design controller
Obtain model
Interface
Select inputs, outputs
OS Robust Controller
HW Robust Controller
Decide External signals
Interface
Obtain model
Data driven modeling (System Identification): 2 benchmarks each from SPECint, SPECfp and PARSEC
Set controller
parameters
§ Output deviation bounds § Input weights § Input discretization § Uncertainty guardband
Design controller
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Evaluation
Coordinated heuristics
Yukta: Multilayer robust
Monolithic non-robust
Average across 8 PARSEC and 6 SPEC (multiprogrammed) workloads
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[ISCA’16] Industry based
Yukta makes the system 37% faster with 20% lower energy ⇒ 50% better ED
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Summary ▪ Dynamic resource management must meet many goals simultaneously
▪ Resource controllers should be modular and coordinated
▪ We propose using Robust Control Theory for computer management – Optimized for uncertainty
▪ We develop Yukta for formal multilayer resource management
▪ Prototype demonstrates significant advancement – 50% reduced Energy×Delay on average
▪ Yukta is essential for resource efficient computing
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Concluding Remarks ▪ More details in the paper – Mathematical background of the Robust Controller
– Yukta design details
– Prototype design choices
– Comparison with other designs and heterogeneous workloads
– Sensitivity analysis
▪ Future work – Heterogeneous components in a layer
– Hierarchical organization of controllers
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Yukta: Energy×Delay minimization
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Yukta: Energy×Delay minimization
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Case Study with blackscholes
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Yukta: blackscholes
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Yukta: Comparison with LQG control
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Yukta: Heterogeneous Workloads
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Yukta: Sensitivity to Uncertainty Guardbands
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Yukta: Sensitivity to Output Bounds
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Yukta: Sensitivity to Input Weights
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