1. Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, 20021 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

2. Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, 20022 Presentation Outline  Mobile CPU Power Efficiency With Demanded Performance  Thermal Scheduling For Mobile Microprocessor  Power Constrained Performance  Observations/Conclusions

3. Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, 20023 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 email, caller-id, reminder and other none high performance w/ anywhere-anytime requested apps

4. Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, 20024 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 Email titles Calendar reminder Pages/voice message

5. Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, 20025 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

6. Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, 20026 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

7. Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, 20027 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

8. Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, 20028 Enhance Effectiveness Of Other Power Control Techniques Dynamic Clock Disabling/Throttling Dynamic Frequency Scaling

9. Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, 20029 Power Constrained Clock Frequency With Performance Impact

10. Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, 200210 Thermal Effects on Power Divide total power into two components: dynamic and leakage power

11. Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, 200211 Thermal Effects on Energy Using power per frequency (W/MHz) metric as proxy for energy

12. Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, 200212 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%

13. Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, 200213 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 0.000 2.000 4.000 6.000 8.000 10.000 12.000 14.000 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 0.000 2.000 4.000 6.000 8.000 10.000 12.000 14.000 16.000 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

14. Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, 200214 Comparative Outcomes: Energy-CPU Time Metric Total Energy x CPU Time

15. Thermal-Scheduling For Ultra Low Power Mobile Microprocessor May, 200215 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