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diff --git a/evaluation.tex b/evaluation.tex index bd10ae3..bcaba88 100644 --- a/evaluation.tex +++ b/evaluation.tex @@ -158,7 +158,7 @@ This guarantee in itself provides a significant leap in terms of HLS reliability The top graphs of Fig.~\ref{fig:polybench-div} and Fig.~\ref{fig:polybench-nodiv} compare the execution time of the 27 programs executed by \vericert{} and the different optimisation levels of \legup{}. Each graph uses optimised \legup{} as the baseline. When division/modulo operations are present \legup{} designs execute around 27$\times$ faster than \vericert{} designs. However, when division/modulo operations are replaced by the iterative algorithm, \legup{} designs are only 2$\times$ faster than \vericert{} designs. The benchmarks with division/modulo replaced show that \vericert{} actually achieves the same execution speed as \legup{} without LLVM optimisations and without operation chaining, which is encouraging, and shows that the hardware generation is following the right steps. The execution time is calculated by multiplying the maximum frequency that the FPGA can run at with this design, by the number of clock cycles that are needed to complete the execution. We can therefore analyse each separately. First, looking at the difference in clock cycles, \vericert{} produces designs that have around 4.5$\times$ as many clock cycles as \legup{} designs in both cases, when division/modulo operations are enabled as well as when they are replaced. This performance gap can be explained in part by LLVM optimisations, which seem to account for a 2$\times$ decrease in clock cycles, as well as operation chaining, which decreases the clock cycles by another 2$\times$. The rest of the speed-up is mostly due to \legup{} optimisations such as scheduling and memory analysis, which are designed to extract parallelism from input programs. -This gap does not represent the performance cost that comes with formally proving a HLS tool. +This gap does not represent the performance cost that comes with formally proving an HLS tool. Instead, it is simply a gap between an unoptimised \vericert{} versus an optimised \legup{}. As we improve \vericert{} by incorporating further optimisations, this gap should reduce whilst preserving the correctness guarantees. |