Hardware/Software Mechanisms for Cross-Layer Power Proportionality “Power Prop” Alex Yakovlev, Andrey Mokhov, Sascha Romanovsky, Max Rykunov, Alexei Iliasov and Danil Sokolov, Schools of EEE and CS, Newcastle University Power Prop The more you get The more you give!

Moore’s law and Power trends

Part I: Power Proportionality

Power Proportionality Issues reported in literature: Source: S. Dawson-Haggerty et al. Power Optimization – Reality Check, UC Berkeley, 2009 Performance -power tradeoff for commodity systems is linear; the best strategy is “Race to sleep”; additional “run” power states are of little use; changes in existing commodity operating systems have little influence The focus should be on the time to transition to and from sleep! For a new type of systems such as WSN there is a non-linear region – the slogan is: learn how to run CMOS slowly and exploit scheduling optimizations Core i7 power drawn at different frequencies

Power proportionality Service-modulated processing Energy-modulated processing

Part II: Reconfigurable Processors

Achieving Power Proportionality Support for wide range of voltages – Asynchronous design – Unstable voltage supply (energy harvesting) Components optimised for different modes – Survival mode (power) – Mission mode (energy efficiency) – Emergency mode (performance) Reconfigurable instructions – Altering instruction behaviour in runtime

Pathway from a high-level specification a low-level MCU implementation CS + EE EE CS + EE Chip design Chip tapeout Chip Testing

DP3(x, y) = x 1 y 1 + x 2 y 2 + x 3 y 3 Reconfigurable Instructions

Resource-level refinement Functionality: DP3(x, y) = x 1 y 1 + x 2 y 2 + x 3 y 3 Abstract specification: Initialisation: c := 0 Invariant: (c = 1) => (res = x 1 y 1 + x 2 y 2 + x 3 y 3 ) Event: if (c = 0) then (res := x 1 y 1 + x 2 y 2 + x 3 y 3 & c := 1) Open the black box and show what is inside: - Perform multiplications by 2-input fast multipliers - Perform addition by 3-input adder

Fastest 2 multipliers Least peak power Dedicated component Balanced Reconfigurable Instructions

x=1 y=0 z=1

Part III: Intel 8051

Final remarks Towards power proportionality – Voltage range: 0.2V – 1.5V – Performance range: 2.7K – 67M instructions/sec Survival of components – Full capability mode: 0.89V – 1.5V – RAM fails at 0.89V – Program counter unreliable below 0.74V – Asynchronous control survives until 0.2V

PCB board for evaluation 16 PCB board with FPGA

Conference and journal papers: – Towards Reconfigurable Processors for Power-Proportional Computing, A. Mokhov, M. Rykunov, D. Sokolov and A. Yakovlev, Proceedings of the 12th IEEE Low Voltage Low Power Conference (FTFC), Paris, France, – Design-for-Adaptivity of Microarchitectures, M. Rykunov, A. Mokhov, D. Sokolov, A. Yakovlev and A. Koelmans, Proceedings of the 24th IEEE International Conference on Application-specific Systems, Architectures and Processors, Washington D.C., USA, – Synthesis of processor instruction sets from high-level ISA specifications, A. Mokhov, M. Rykunov, D. Sokolov, A. Yakovlev, A. Iliasov, and A. Romanovsky. IEEE Transactions on Computers, – Design of Processors with Reconfigurable Microarchitecture, A. Mokhov, M. Rykunov, D. Sokolov, and A. Yakovlev, Journal of Low Power Electronics and Applications, (Under review). 17 Project outcomes:

18 Project outcomes (cont.): Several MSc projects PhD thesis – “Design of Asynchronous Microprocessor for Power Proportionality” (Nov. 2013). The PowerProp project established several important industrial connections, e.g. Maxeler Technologies, IBM Research, etc. Some PowerProp theory, tool support and software ideas have moved to a new Programme Grant -- PRiME (EP/K034448/1). CPU design ideas will be used in SAVVIE project ( EP/K012908/1). Helped to promote joint CS+EE developments in Workcraft (graph-based EDA environment), used in several EPSRC projects.

Thank you!

20 Parameterised Graphs for formal specification of Multi-modal systems DP3 instruction computes dot product x·y = x1·y1 + x2·y2 + x3·y3. –declaration of the functional units a = unit "2-input adder" b = unit “3-input adder" c = unit “2-input multiplier" d = unit "fast 2-input multiplier" e = unit "dedicated DP3 unit“ –specification of each instruction inst_a = (d1 + d2 + d3) -> b inst_b = c1 -> c1 1 -> c1 -> b inst_c = e inst_d = (c2 + c1) -> a + c1 -> c1 -> a inst_e = d1 -> d1 -> (a + c1) -> a

23 Parameterised Graphs for formal specification of Multi-modal systems DP3 instruction computes dot product x·y = x1·y1 + x2·y2 + x3·y3. –declaration of the functional units a = unit "2-input adder" b = unit “3-input adder" c = unit “2-input multiplier" d = unit "fast 2-input multiplier" e = unit "dedicated DP3 unit“ –specification of each instruction inst_a = (d1 + d2 + d3) -> b inst_b = c1 -> c1 1 -> c1 -> b inst_c = e inst_d = (c2 + c1) -> a + c1 -> c1 -> a inst_e = d1 -> d1 -> (a + c1) -> a

Intel 8051 Instruction Set

CJNE Instruction

Branch takenBranch not taken

Measurements: Current & Latency

Measurements: Power

Measurements: Energy Efficiency

Some measurements… V to 1.5V: full capability mode. 0.74V to 0.89V: at 0.89V the RAM starts to fail, so the chip can only operate using internal registers. 0.22V to 0.74V: at 0.74V the program counter starts to fail, however the control logic synthesised using the CPOG model continues to operate correctly down to 0.22V 67 MIPS at 1.2 V. ~2700 instructions per second at 0.25V.