Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, Thermal-Scheduling For Ultra Low Power Mobile Microprocessor George Cai 1 Chee How Lim 1 W. Robert Daasch 2 Intel Corporation 1 Integrated Circuit Design and Test Laboratory PSU 2

Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, Presentation Outline  Mobile CPU Power Efficiency With Demanded Performance  Thermal Scheduling For Mobile Microprocessor  Power Constrained Performance  Observations/Conclusions

Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, Ultra Low Power Mobile Microprocessor Primary pipeline: maximal performance, complex pipeline structure Second pipeline: Minimum power and energy consumption, very simple in order structure and target mobile anywhere-anytime applications. Transparent to OS and applications Maximal utilizing on die clock/power gating for energy saving FEDE EX RF DE IOP OOP Primary Secondary Majority mobile apps with performance requirements Text , caller-id, reminder and other none high performance w/ anywhere-anytime requested apps

Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, Low Energy Consumption With Providing Suitable Performance Is Key For “Anywhere And Anytime” Must be compatible with exist OS and platform Must have active leakage power control Must meet the real time telecom application requirements Stock/Urgent Messages Stock Update Alert Interactive command and reply All urgent message And important news News headline titles Calendar reminder Pages/voice message

Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, Runtime Thermal Scheduling Capability FEDE EX RF DE IOP OOP Primary Secondary When thermal threshold is exceeded, the pipeline clusters will service instructions in alternating manner: cool the “hot” pipeline by clock/power-gating & the “cold” pipeline sustains processor operations Flexible selecting the threshold point, the energy-delay product, performance, and reliability of the processor can be enhanced

Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, Thermal Effects: Leakage Trend Active leakage power reduction will be significant role for total power reduction Thermal control is important for low energy consumption for mobile CPU Derived from F. Pollack’s Micro-32 Keynote Presentation, 1999

Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, Example of Scheduling Algorithm S1: Normal Operation (Primary Pipeline) S2: Stall Fetch & Clear Pipeline S3: Alternate Operation (Secondary Pipeline) S4: Disable Clock or Scale F-V S1 S2 S3 T 1 < T H S4 T 1  T H T 1  T L T 1 > T L & T 2 < T H T 1 > T L & T 2  T H T 1 > T L || T 2 > T L T 1  T L & T 2  T L T S2 T S1 Temperature (  C) TaTa T max t cycle THTH t cool t heat Time (s) TLTL

Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, Enhance Effectiveness Of Other Power Control Techniques Dynamic Clock Disabling/Throttling Dynamic Frequency Scaling

Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, Power Constrained Clock Frequency With Performance Impact

Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, Thermal Effects on Power Divide total power into two components: dynamic and leakage power

Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, Thermal Effects on Energy Using power per frequency (W/MHz) metric as proxy for energy

Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, Architecture-Level Power-Performance Tradeoff For wide-superscalar processors, performance impact of pipeline scaling is smaller than global clock throttling or frequency scaling ~15% ~30%

Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, Comparative Outcomes: Energy Metric Simulation Conditions (500 million instructions; T L = 55  C) –Stop Clock Control: Toggle between F max and 0 MHz –Voltage/Freq Scaling: Toggle between F max and 0.9/0.8/0.6 F max –Thermal Scheduling: Toggle between Primary and 2nd Pipelines Clk gating V-F scaling Thermal scheduling M88KSIM LI GCC PERL Energy (J) Thermal Control Techniques Benchmarks Energy Consumption of Conservative Control M88KSIM LI GCC PERL Clk Gating F-V Scaling Thermal Scheduling M88KSIM LI GCC PERL Energy (J) Thermal Control Techniques Benchmarks Energy Consumption of Aggressive Control M88KSIM LI GCC PERL Conservative: T H = 70  C Aggressive: T H = 60  C

Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, Comparative Outcomes: Energy-CPU Time Metric Total Energy x CPU Time

Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, Pros and Cons Advantages Limits power/energy upper bound & prevents thermal runaway Pipeline tuned for either performance or ultra low power Existing OS and application compatible Performance penalty for engaging/disengaging control is small (architecture event) Supports low-power anywhere-anytime of mobile computing  Non-timing critical tasks  Real-time application that requires more predictable output Concerns  i/  t during pipeline switch Real-Register File may require extra dedicated ports Bypass bus may have additional loading