Targeting code diversity with run-time adjustable issue-slots in a chip multiprocessor

Abstract

This paper presents an adaptable softcore chip multiprocessor (CMP). The processor instruction set architecture (ISA) is based on the VEX ISA. The issue-width of the processor can be adjusted at run-time (before an application starts). The processor has eight 2-issue cores that can run independently from each other. If not in use, each core can be taken to a lower power mode by gating off its source clock. Multiple 2-issue cores can be combined at run-time to form a variety of configurations of very long instruction word (VLIW) processors. The CMP is implemented in the Xilinx Virtex-6 XC6VLX240T FPGA. It has a single ISA and requires no specialized compiler support. The CMP can target a variety of applications having instruction and/or data level parallelism. We found that applications/kernels with larger instruction level parallelism (ILP) performs better when run on a larger issue-width core, while applications with larger data level parallelism (DLP) performs better when run on multiple 2-issue cores with the data distributed among the cores.