Commit 9691c549 authored by Dominic Etienne Charrier's avatar Dominic Etienne Charrier
Browse files

21_distributed-memory.tex: Add some description text. Needs some polishing (later).

parent e7997263
......@@ -390,19 +390,21 @@ proper load balancings.
Furthermore, we recommend that you use the a non-greedy load
metric if you switch this feature on (\texttt{hotspot}, e.g.).
\subsection{Weak and strong scaling}
\subsection{Meshes for weak and strong scaling}
TODO
ExaHyPE distributes work by decomposing the tripartitioned spacetree into
subtrees that are deployed to worker processes.
Only subtrees that overlap with the computational domain are deployed.
This constraint can be used to steer work distribution.
\begin{figure}[h]
\begin{center}
\includegraphics[width=0.5\textwidth]{sketches/strong-scaling-grid-223.pdf}
\end{center}
\caption{%
A grid with $36^d$ cells on the coarse grid which allows to use $1$, $2^d$, $4^d$, and $12^d$ ranks
to uniformly distribute the load.
}
\end{figure}
ExaHyPE can scale the bounding box such that \texttt{outside\_cells\_left} and/or \texttt{outside\_cells\_right} cells are placed outside of the
domain while the latter is still resolved as accurately as specified in the spec file.
Furthermore, there is an option to place exactly \texttt{ranks\_per\_dimension" on the coarse grid}.
(Note: This overrules \texttt{outside\_cells\_right} but not \texttt{outside\_cells\_left}.
This feature is particular interesting for weak scaling experiments as it can scale the number of cells per dimension
of a mesh by arbitrary integers.
An example is given below:
\begin{figure}[h]
\begin{center}
......@@ -417,6 +419,22 @@ TODO
}
\end{figure}
The bounding box scaling controls can be used to create interesting meshes as
the $36^d$ cell mesh given below. This mesh was created with 9 outside cells
on the left side and 12 ranks per dimension. The mesh
is interesting since it can be perfectly distributed among
$2^d$, $4^d$, and $12^d$ processes.
\begin{figure}[h]
\begin{center}
\includegraphics[width=0.5\textwidth]{sketches/strong-scaling-grid-223.pdf}
\end{center}
\caption{%
A grid with $36^d$ cells on the coarse grid which allows to use $1$, $2^d$, $4^d$, and $12^d$ ranks
to uniformly distribute the load.
}
\end{figure}
\section{MPI troubleshooting and inefficiency patterns}
\label{section:mpi:inefficiency-patterns}
......
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