Multi-cellular paradigm

1. Multi-cellular paradigm • The molecular level can support self-replication (and self-repair). • But we also need cells that can be designed to fit the specific application and at the same time able to support bio-inspired mechanisms for self-replication and fault tolerance.

2. Cellular differentiation • Cells adapt their physical structure to fit the “application” • Can circuits/processors do the same? • Physically? No • Logically? Yes, but… • Can they do it easily (dare we say, automatically)?

3. The MOVE paradigm • One single instruction : move • Data displacements trigger operations • Architecture based around data ≠ operation centric • Regular structure : functional units + data network • Scalable and modular architecture Example: Sum of two values Conventional architecture: add R1, R2, R3; MOVE architecture: move O(Fxxx), I1(Fsum) move O(Fyyy), I2(Fsum) move O(Fsum), I(Fzzz)

4. Genotype Layer • Phenotype Layer • Mapping Layer Example – Automatic Synthesis Application-specific (parallel) functions Developmental algorithm Genetic code

5. Phenotype Layer Cell design and specialization Within a MOVE framework, the specialization (differentiation) of a cell corresponds to the selection of the functional and communication units that can most efficiently implement the desired application. Application code (parallel)

6. Hardware/software co-design • Co-design of a system : tailor an hardware system for a specific application which can then exploit the synergism of that hardware and software. • In a MOVE context (but also generally), this amounts to defining the structure of the processor (data size, number of busses, functional and communication units, etc.) at the same time as the program that runs on the processor. • HW/SW co-design is a task for the compiler. • Hardware-Software Partitioning • Purpose: determine which parts of an algorithm (or a program) are the best candidates to be implemented in hardware • Optimization goal : minimize execution time and/or hardware area • Constraints: hardware size and/or execution time • It’s an known NP-hard problem.

7. FU extraction • Extracting the optimal FUs from the code is a complex problem!

8. FU extraction • How about having a quick peek at biology? • Idea: let us use evolution!! • In fact, this approach is much closer to biology than simply evolving code: in nature, the hardware (the cell) and the software (the genome) have evolved together!

9. FU extraction • Idea: let us use evolution to determine which FU should be implemented for a given program, starting from a given hardware budget and a “minimal” processor

10. FU extraction • First step: profiling the code (standard compilation technique)

11. FU extraction • Second step: transform into tree (standard compilation technique), then define a field to determine if parts of the tree should be turned into hardware. • Third step: represent as 1-D genome (standard EA technique) • Fourth step: run the EA (with some fancy optimizations)

12. Fitness evaluation s = size of the new processor t = execution time of the program on the new processor α = execution time of the program on a minimal processor β= hardware area to implement the minimal processor (which has, by definition, a fitness of 1) hwLimit = maximum hardware allowed to implement the new processor • Note: • Relative fitness function • When out of allowed hardware range, logarithmic decrease • The hardware investment has to be small enough to be retained

13. Determining hardware size • How can the size of the new FU estimated (the β parameter of the fitness) ? • The idea: • Determine the size of each basic building block (+, - , AND, …) • Compute how many of them are used for a new FU • Add a cost for the bus interface • The characterization has to be done for every target platform.

14. Determining hardware execution time • Use the same idea used for size to calculate execution time: • Compute the time needed for each building block • Take targeted clock period as a basis • When time estimated > clock period, add 1 to the total time  small jumps in the fitness landscape

15. Improvements • Biggest problem with the approach presented : not very competitive because of the search space size • Does not converge to a solution in reasonable time • VAST amount of “junk” solutions • How can we improve the performance? How about using some heuristics? • Try to reuse the inferred FU at different places in the program • Remove “useless” FUs

16. Pattern-matching optimization • How to find reusable FUs ? • The GA behaves a bit like random mutations  difficult to find reusability this way • Solution: search the whole tree each time a new HW block is defined to replace similar pieces of code

17. Non-optimal block pruning • “Cleaning” phase made at each generation of the algorithm • Removes HW blocks that are non-optimal from the fitness point-of-view • To see if a block is useful, compute the fitness with and without this block implemented in HW. If the software solution has a better fitness, the block is non-optimal and can be removed.

18. DOMAIN STANDARD FU extraction - Interface

20. FU extraction - Results • Example (functions from FACT factorization algorithm): • Hardware increase (estimated): 10% (fixed) • Speedup (estimated): 2.27 (227%) • Other results: • All were obtained in a few seconds

21. Problem solved? • Evolution allows the extraction of FUs according to arbitrary criteria: • Performance • Size • Power consumption • Reliability • Any other… and in any combination • It also generates a range of solutions, allowing the engineer to choose among several options • Problem solved? • Definitely not… co-design is a HARD problem and a lot remains to be explored.

22. Can Nature help? • Metabolic pathways • Immune systems • Stem cells • Regeneration • Homeostasis • Developmental plasticity • etc… For all of these, an efficient mapping to hardware remains an open research topic