PathSeeker: A Fast Mapping Algorithm for CGRAs

Coarse-grained reconfigurable arrays (CGRAs) have gained traction over the years as a low-power accelerator due to the efficient mapping of the compute-intensive loops onto the 2-D array by the CGRA compiler. When encountering a mapping failure for a given node, existing mapping techniques either exit and retry the mapping anew, or perform backtracking, i.e., recursively remove the previously mapped node to find a valid mapping. Abandoning mapping and starting afresh can deteriorate the quality of mapping and the compilation time. Even backtracking may not be the best choice since the previous node may not be the incorrectly placed node. To tackle this issue, we propose PathSeeker - a mapping approach that analyzes mapping failures and performs local adjustments to the schedule to obtain a mapping. Experimental results on 35 top performance-critical loops from MiBench, Rodinia, and Parboil benchmark suites demonstrate that PathSeeker can map all of them with better mapping quality and dramatically less compilation time than the previous state-of-the-art approaches - GraphMinor and RAMP, which were unable to map 20 and 5 loops, respectively. Over these benchmarks, PathSeeker achieves 28% better performance at 550x compilation speedup over GraphMinor and 3% better performance at 10x compilation speedup over RAMP on a 4x4 CGRA.