Scheduling for Energy Performance and Reliability Yavuz Yetim Princeton University

Why 3D* Management ? Perfect solution is not required eg: video, sound apps, games, … Utilize efficient algorithms** designed for unreliable systems Better trade-off Easier and faster design Less necessity for verification Introduction of reliability to the problem * Energy-Performance-Reliability ** [Kim, Shanbhag]

An Example Algorithm* Requires a certain limit on unreliability Cannot manage hardware for each new application Another layer of management required * [Kim, Shanbhag]

Resource Management What are the resources? – Cores: Frequency Power Reliability What are the users of those resources? – Threads Error Rate Workload Finish Time SCHEDULE THREADS ON RESOURCES WITH CORRECT TIMING

Scheduling Objective – Can be either of Energy (Our choice) Performance (To constraints: Deadline) Reliability (To constraints: Expected Number of Errors) Constraints – Mutual exclusion – Sequencing – Expected Number of Errors – Deadline

Scheduling Constraints Thread 1: Thread 2: Tasks t1t2t3 t1 t2 t3 t4 Core 1 (f) : Core 2 (0.5 f) : t1 t2 t3 t4 : 2: 4 Time

Scheduling Objective Current energy model (only busy time): – Thread migration + P busy * T busy + P idle * T idle ALL FORMULATED IN INTEGER LINEAR PROGRAMMING

Novelties of this Approach A systematic scheduling solution in ILP to a system with: Heterogeneous Cores Threads having different requirements Inter-thread dependency Thread migration overhead (both as energy and time) Gain from energy sacrificing either of Performance Reliability to the limit imposed by the software ?

How is this useful ? Size: Speed Darkness: Reliability Numbers: Power Size: Workload Darkness: ENE Numbers: Deadline initA() calculateA() initC() initD() calculateC() calculateD() initE() calculateE() calculateCE() 1000 ms800 ms700 ms 50W150W 75W50W formGraph() optimize()

Related Background Multiprocessor scheduling under precedence constraints: Polyhedral results [Coll, Riberio, Souza] – ILP formulation of the basic multiprocessor scheduling No definition of a thread (thread specific parameters are not valid: Performance, Reliability, etc…) – Mathematical result No interpretation of the concept – No reliability An ILP Formulation for Task Scheduling on Heterogeneous Chip Multiprocessors [Tosun, Mansouri, Kandemir, Ozturk] – 3D approach to the problem No definition of a thread (thread specific parameters are not valid: Performance, Reliability, etc…) Unrealistic Reliability Model Unrealistic Reliability Parameters – No direction about how to deploy the system

Future Work Improved Imprecision Model – A better statistical model – Imprecision defined on data Dynamic control – In case statistics are not enough Online management of cores – Online modification of core parameters (eg: DVFS) Software Language Support

Conclusion Different perspective to a known problem Managing complexity of HW/SW interface – Satisfying needs of the layers with abstraction Mathematically and systematically neat approach General solution with a detailed model

Thank you Questions ??? Questions ???