Improving Conservative VHDL Simulation Performance by Reduction of Feedback

Abstract

This paper describes two forms of feedback in the simulation runtime of VHDL circuits that greatly influences performance. While circuit feedback and strongly connected components have been observed and documented as detrimental influences to conservative parallel discrete event simulation (PDES) efficiency, that influence has never been quantified. Moreover, in this study, the phenomenon of induced feedback was observed to diminish speedup to the same degree as explicit feedback. In this paper the influence of feedback on simulation runtime is analyzed and an algorithm for its elimination is presented. In addition, a metric for the quantification of feedback is introduced. By measuring feedback, it is possible to balance its influence on simulation runtime with that of other factors (e.g. load balance, number of processors, machine granularity, etc. ) through the use of a cost-based partitioning approach. This paper reports significant improvements in runtime for three circuits due to the prevention of feedback using the partitioning algorithm presented. In addition, strong correlation between the feedback metric and conservative parallel simulation overhead is demonstrated.