GPU-Accelerated Wire-Length Estimation for FPGA Placement

In the FPGA design flow, placement remains one of the most time-consuming stages, and is also crucial in terms of quality of result. HPWL and Star+ are widely used as cost metrics in FPGA placement for estimating the total wire-length of a candidate placement prior to routing. However, both wire-length models are expensive to compute requiring O(nm) time, where n is the number of nets and m is the average net cardinality. This paper proposes using the massively multi-threaded architecture provided by GPUs to reduce the time required to compute HPWL and Star+. First, a specialized set of data structures is developed for storing net-connectivity information on the GPU. Next, a study is performed to determine how to best map the data structures onto the GPU to exploit the heterogeneous memories and thread-level parallelism that are available. Finally, a study is performed to determine what effect circuit size and net cardinality have on the speedups that can be achieved. Overall, the results show that speedups of as much as 160x over a serial CPU implementation can be achieved for both models when tested using standard benchmarks.