# HG changeset patch
# User Ashwin Vishnu <avmo@kth.se>
# Date 1543604537 -3600
#      Fri Nov 30 20:02:17 2018 +0100
# Node ID 9bebe5b1e3d786a3ff98cad849c9016c63137450
# Parent  a3bcea4ef8576d63dacd00a2aaf4333e4fd090d3
FluidSim: comparison with sequential walltimes

diff --git a/fluidsim/fluidsim_paper.tex b/fluidsim/fluidsim_paper.tex
--- a/fluidsim/fluidsim_paper.tex
+++ b/fluidsim/fluidsim_paper.tex
@@ -687,10 +687,12 @@
 \subsubsection*{Scalability}
 
 Scalability can be quantified by speedup $S$ which is a measure of the time taken
-to complete $N$ iterations for different number of processes, $n_p$.  We shall
-refrain from comparing sequential runs in this context, since the operators used
-for the sequential mode differ from the parallel mode, especially the FFT
-class. Speedup is formally defined here as:
+to complete $N$ iterations for different number of processes, $n_p$.
+%We shall
+%refrain from comparing sequential runs in this context, since the operators used
+%for the sequential mode differ from the parallel mode, especially the FFT
+%class.
+Speedup is formally defined here as:
 
 \begin{equation}
 S_\alpha(n_p) = \frac
@@ -743,6 +745,30 @@
 \fluidpack{fft}, namely \codeinline{fft2d.mpi\_with\_fftw1d} and
 \codeinline{fft2d.mpi\_with\_fftwmpi2d}.
 
+Although the FFT classes are different for sequential and parallel
+runs, for the sake of comparison, we have tabulated the actual
+walltime elapsed in Table~\ref{table:seqpar}. Clearly due to the differences
+in the implementations, for \codeinline{fftw1d}-based classes it takes a
+performance hit with parallelization, while for classes based on
+\codeinline{fftw2d} the performance improves.
+
+\begin{table}
+\centering
+\begin{tabular}{lrlr}
+\hline
+ FFT class &   Time ($n_p=1$) &   FFT class & Time ($n_p=2$)  \\
+\hline
+  \codeinline{fft2d.with\_fftw1d}  & 6.63   &
+  \codeinline{fft2d.mpi\_with\_fftw1d}    & 7.63 \\
+  \codeinline{fft2d.with\_fftw2d}  &  5.59  &
+  \codeinline{fft2d.mpi\_with\_fftwmpi2d} &  3.91 \\
+\hline
+\end{tabular}
+\caption{Elapsed times (in seconds) for twenty time steps of 1024 x 1024 case
+with the 2D Navier-Stokes 2D (\codeinline{fluidsim.solvers.ns2d}) solver.}
+\label{table:seqpar}
+\end{table}
+
 \begin{figure}[htp]
 \centering
 \includegraphics[width=\linewidth]{tmp/fig_bench_strong2d}