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revision 1.21 by edhill, Tue Apr 4 15:54:55 2006 UTC revision 1.22 by edhill, Tue Apr 4 18:33:52 2006 UTC
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1  % $Header$  % $Header$
2    
3  This chapter focuses on describing the {\bf WRAPPER} environment within which  This chapter focuses on describing the {\bf WRAPPER} environment
4  both the core numerics and the pluggable packages operate. The description  within which both the core numerics and the pluggable packages
5  presented here is intended to be a detailed exposition and contains significant  operate. The description presented here is intended to be a detailed
6  background material, as well as advanced details on working with the WRAPPER.  exposition and contains significant background material, as well as
7  The tutorial sections of this manual (see sections  advanced details on working with the WRAPPER.  The tutorial sections
8  \ref{sect:tutorials}  and \ref{sect:tutorialIII})  of this manual (see sections \ref{sect:tutorials} and
9  contain more succinct, step-by-step instructions on running basic numerical  \ref{sect:tutorialIII}) contain more succinct, step-by-step
10  experiments, of varous types, both sequentially and in parallel. For many  instructions on running basic numerical experiments, of varous types,
11  projects simply starting from an example code and adapting it to suit a  both sequentially and in parallel. For many projects simply starting
12  particular situation  from an example code and adapting it to suit a particular situation
13  will be all that is required.  will be all that is required.  The first part of this chapter
14  The first part of this chapter discusses the MITgcm architecture at an  discusses the MITgcm architecture at an abstract level. In the second
15  abstract level. In the second part of the chapter we described practical  part of the chapter we described practical details of the MITgcm
16  details of the MITgcm implementation and of current tools and operating system  implementation and of current tools and operating system features that
17  features that are employed.  are employed.
18    
19  \section{Overall architectural goals}  \section{Overall architectural goals}
20  \begin{rawhtml}  \begin{rawhtml}
# Line 25  Broadly, the goals of the software archi Line 25  Broadly, the goals of the software archi
25  three-fold  three-fold
26    
27  \begin{itemize}  \begin{itemize}
28  \item We wish to be able to study a very broad range  \item We wish to be able to study a very broad range of interesting
29  of interesting and challenging rotating fluids problems.    and challenging rotating fluids problems.
30  \item We wish the model code to be readily targeted to  \item We wish the model code to be readily targeted to a wide range of
31  a wide range of platforms    platforms
32  \item On any given platform we would like to be  \item On any given platform we would like to be able to achieve
33  able to achieve performance comparable to an implementation    performance comparable to an implementation developed and
34  developed and specialized specifically for that platform.    specialized specifically for that platform.
35  \end{itemize}  \end{itemize}
36    
37  These points are summarized in figure \ref{fig:mitgcm_architecture_goals}  These points are summarized in figure
38  which conveys the goals of the MITgcm design. The goals lead to  \ref{fig:mitgcm_architecture_goals} which conveys the goals of the
39  a software architecture which at the high-level can be viewed as consisting  MITgcm design. The goals lead to a software architecture which at the
40  of  high-level can be viewed as consisting of
41    
42  \begin{enumerate}  \begin{enumerate}
43  \item A core set of numerical and support code. This is discussed in  \item A core set of numerical and support code. This is discussed in
# Line 71  is required. Line 71  is required.
71  \begin{center}  \begin{center}
72  \resizebox{!}{2.5in}{\includegraphics{part4/mitgcm_goals.eps}}  \resizebox{!}{2.5in}{\includegraphics{part4/mitgcm_goals.eps}}
73  \end{center}  \end{center}
74  \caption{  \caption{ The MITgcm architecture is designed to allow simulation of a
75  The MITgcm architecture is designed to allow simulation of a wide    wide range of physical problems on a wide range of hardware. The
76  range of physical problems on a wide range of hardware. The computational    computational resource requirements of the applications targeted
77  resource requirements of the applications targeted range from around    range from around $10^7$ bytes ($\approx 10$ megabytes) of memory to
78  $10^7$ bytes ( $\approx 10$ megabytes ) of memory to $10^{11}$ bytes    $10^{11}$ bytes ($\approx 100$ gigabytes). Arithmetic operation
79  ( $\approx 100$ gigabytes). Arithmetic operation counts for the applications of    counts for the applications of interest range from $10^{9}$ floating
80  interest range from $10^{9}$ floating point operations to more than $10^{17}$    point operations to more than $10^{17}$ floating point operations.}
 floating point operations.}  
81  \label{fig:mitgcm_architecture_goals}  \label{fig:mitgcm_architecture_goals}
82  \end{figure}  \end{figure}
83    
# Line 87  floating point operations.} Line 86  floating point operations.}
86  <!-- CMIREDIR:wrapper: -->  <!-- CMIREDIR:wrapper: -->
87  \end{rawhtml}  \end{rawhtml}
88    
89  A significant element of the software architecture utilized in  A significant element of the software architecture utilized in MITgcm
90  MITgcm is a software superstructure and substructure collectively  is a software superstructure and substructure collectively called the
91  called the WRAPPER (Wrappable Application Parallel Programming  WRAPPER (Wrappable Application Parallel Programming Environment
92  Environment Resource). All numerical and support code in MITgcm is written  Resource). All numerical and support code in MITgcm is written to
93  to ``fit'' within the WRAPPER infrastructure. Writing code to ``fit'' within  ``fit'' within the WRAPPER infrastructure. Writing code to ``fit''
94  the WRAPPER means that coding has to follow certain, relatively  within the WRAPPER means that coding has to follow certain, relatively
95  straightforward, rules and conventions (these are discussed further in  straightforward, rules and conventions (these are discussed further in
96  section \ref{sect:specifying_a_decomposition}).  section \ref{sect:specifying_a_decomposition}).
97    
98  The approach taken by the WRAPPER is illustrated in figure  The approach taken by the WRAPPER is illustrated in figure
99  \ref{fig:fit_in_wrapper} which shows how the WRAPPER serves to insulate code  \ref{fig:fit_in_wrapper} which shows how the WRAPPER serves to
100  that fits within it from architectural differences between hardware platforms  insulate code that fits within it from architectural differences
101  and operating systems. This allows numerical code to be easily retargetted.  between hardware platforms and operating systems. This allows
102    numerical code to be easily retargetted.
103    
104    
105  \begin{figure}  \begin{figure}
# Line 416  default WRAPPER sources, because of thei Line 416  default WRAPPER sources, because of thei
416  \subsection{Distributed memory communication}  \subsection{Distributed memory communication}
417  \label{sect:distributed_memory_communication}  \label{sect:distributed_memory_communication}
418  Many parallel systems are not constructed in a way where it is  Many parallel systems are not constructed in a way where it is
419  possible or practical for an application to use shared memory  possible or practical for an application to use shared memory for
420  for communication. For example cluster systems consist of individual computers  communication. For example cluster systems consist of individual
421  connected by a fast network. On such systems there is no notion of shared memory  computers connected by a fast network. On such systems there is no
422  at the system level. For this sort of system the WRAPPER provides support  notion of shared memory at the system level. For this sort of system
423  for communication based on a bespoke communication library  the WRAPPER provides support for communication based on a bespoke
424  (see figure \ref{fig:comm_msg}).  The default communication library used is MPI  communication library (see figure \ref{fig:comm_msg}).  The default
425  \ref{mpi}. However, it is relatively straightforward to implement bindings to  communication library used is MPI \cite{MPI-std-20}. However, it is
426  optimized platform specific communication libraries. For example the work  relatively straightforward to implement bindings to optimized platform
427  described in \ref{hoe-hill:99} substituted standard MPI communication for a  specific communication libraries. For example the work described in
428  highly optimized library.  \ref{hoe-hill:99} substituted standard MPI communication for a highly
429    optimized library.
430    
431  \subsection{Communication primitives}  \subsection{Communication primitives}
432  \label{sect:communication_primitives}  \label{sect:communication_primitives}
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