Just-in-Time Instruction Set Extension - Feasibility and Limitations for an FPGA-Based Reconfigurable ASIP Architecture

In this paper, we study the feasibility of moving the instruction set customization process for reconfigurable ASIPs to runtime under the precondition that current FPGA devices and tools are used. To this end we propose a tool flow for just-in-time ASIP customization which identifies suitable custom instructions to accelerate arbitrary binary applications that execute on a virtual machine. The tool flow targets our previously introduced Woolcano reconfigurable ASIP architecture, which augments the PowerPC core in a Xilinx Virtex 4FX CPU with runtime reconfigurable instructions. We evaluate the tool flow with a comprehensive set of applications from the SPEC2006, SPEC2000, MiBench, and SciMark2 benchmark suites and compare the speedups that can be achieved with the overhead of the complete ASIP specialization process. We show that an average speedup of 5× can be achieved for benchmarks from the embedded computing domain. The overhead of custom instruction identification and hardware generation for these benchmarks is less than 50 minutes and will be compensated if the applications execute for more than 2 hours. Finally, we evaluate caching strategies to reduce the time until this break even point is reached.