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% $Header$ |
% $Header$ |
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In this chapter we describe the software architecture and |
This chapter focuses on describing the {\bf WRAPPER} environment within which |
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implementation strategy for the MITgcm code. The first part of this |
both the core numerics and the pluggable packages operate. The description |
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chapter discusses the MITgcm architecture at an abstract level. In the second |
presented here is intended to be a detailed exposition and contains significant |
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part of the chapter we described practical details of the MITgcm implementation |
background material, as well as advanced details on working with the WRAPPER. |
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and of current tools and operating system features that are employed. |
The tutorial sections of this manual (see sections |
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\ref{sect:tutorials} and \ref{sect:tutorialIII}) |
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contain more succinct, step-by-step instructions on running basic numerical |
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experiments, of varous types, both sequentially and in parallel. For many |
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projects simply starting from an example code and adapting it to suit a |
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particular situation |
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will be all that is required. |
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The first part of this chapter discusses the MITgcm architecture at an |
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abstract level. In the second part of the chapter we described practical |
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details of the MITgcm implementation and of current tools and operating system |
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features that are employed. |
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\section{Overall architectural goals} |
\section{Overall architectural goals} |
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\begin{enumerate} |
\begin{enumerate} |
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\item A core set of numerical and support code. This is discussed in detail in |
\item A core set of numerical and support code. This is discussed in detail in |
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section \ref{sec:partII}. |
section \ref{sect:partII}. |
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\item A scheme for supporting optional "pluggable" {\bf packages} (containing |
\item A scheme for supporting optional "pluggable" {\bf packages} (containing |
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for example mixed-layer schemes, biogeochemical schemes, atmospheric physics). |
for example mixed-layer schemes, biogeochemical schemes, atmospheric physics). |
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These packages are used both to overlay alternate dynamics and to introduce |
These packages are used both to overlay alternate dynamics and to introduce |
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This chapter focuses on describing the {\bf WRAPPER} environment under which |
This chapter focuses on describing the {\bf WRAPPER} environment under which |
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both the core numerics and the pluggable packages function. The description |
both the core numerics and the pluggable packages function. The description |
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presented here is intended to be a detailed exposistion and contains significant |
presented here is intended to be a detailed exposition and contains significant |
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background material, as well as advanced details on working with the WRAPPER. |
background material, as well as advanced details on working with the WRAPPER. |
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The examples section of this manual (part \ref{part:example}) contains more |
The examples section of this manual (part \ref{part:example}) contains more |
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succinct, step-by-step instructions on running basic numerical |
succinct, step-by-step instructions on running basic numerical |
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to ``fit'' within the WRAPPER infrastructure. Writing code to ``fit'' within |
to ``fit'' within the WRAPPER infrastructure. Writing code to ``fit'' within |
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the WRAPPER means that coding has to follow certain, relatively |
the WRAPPER means that coding has to follow certain, relatively |
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straightforward, rules and conventions ( these are discussed further in |
straightforward, rules and conventions ( these are discussed further in |
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section \ref{sec:specifying_a_decomposition} ). |
section \ref{sect:specifying_a_decomposition} ). |
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The approach taken by the WRAPPER is illustrated in figure |
The approach taken by the WRAPPER is illustrated in figure |
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\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 insulate code |
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\caption{ |
\caption{ |
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Numerical code is written too fit within a software support |
Numerical code is written too fit within a software support |
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infrastructure called WRAPPER. The WRAPPER is portable and |
infrastructure called WRAPPER. The WRAPPER is portable and |
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can be sepcialized for a wide range of specific target hardware and |
can be specialized for a wide range of specific target hardware and |
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programming environments, without impacting numerical code that fits |
programming environments, without impacting numerical code that fits |
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within the WRAPPER. Codes that fit within the WRAPPER can generally be |
within the WRAPPER. Codes that fit within the WRAPPER can generally be |
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made to run as fast on a particular platform as codes specially |
made to run as fast on a particular platform as codes specially |
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\end{figure} |
\end{figure} |
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\subsection{Target hardware} |
\subsection{Target hardware} |
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\label{sec:target_hardware} |
\label{sect:target_hardware} |
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The WRAPPER is designed to target as broad as possible a range of computer |
The WRAPPER is designed to target as broad as possible a range of computer |
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systems. The original development of the WRAPPER took place on a |
systems. The original development of the WRAPPER took place on a |
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\subsection{Supporting hardware neutrality} |
\subsection{Supporting hardware neutrality} |
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The different systems listed in section \ref{sec:target_hardware} can be |
The different systems listed in section \ref{sect:target_hardware} can be |
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categorized in many different ways. For example, one common distinction is |
categorized in many different ways. For example, one common distinction is |
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between shared-memory parallel systems (SMP's, PVP's) and distributed memory |
between shared-memory parallel systems (SMP's, PVP's) and distributed memory |
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parallel systems (for example x86 clusters and large MPP systems). This is one |
parallel systems (for example x86 clusters and large MPP systems). This is one |
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class of machines (for example Parallel Vector Processor Systems). Instead the |
class of machines (for example Parallel Vector Processor Systems). Instead the |
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WRAPPER provides applications with an |
WRAPPER provides applications with an |
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abstract {\it machine model}. The machine model is very general, however, it can |
abstract {\it machine model}. The machine model is very general, however, it can |
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easily be specialized to fit, in a computationally effificent manner, any |
easily be specialized to fit, in a computationally efficient manner, any |
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computer architecture currently available to the scientific computing community. |
computer architecture currently available to the scientific computing community. |
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\subsection{Machine model parallelism} |
\subsection{Machine model parallelism} |
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Codes operating under the WRAPPER target an abstract machine that is assumed to |
Codes operating under the WRAPPER target an abstract machine that is assumed to |
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consist of one or more logical processors that can compute concurrently. |
consist of one or more logical processors that can compute concurrently. |
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Computational work is divided amongst the logical |
Computational work is divided among the logical |
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processors by allocating ``ownership'' to |
processors by allocating ``ownership'' to |
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each processor of a certain set (or sets) of calculations. Each set of |
each processor of a certain set (or sets) of calculations. Each set of |
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calculations owned by a particular processor is associated with a specific |
calculations owned by a particular processor is associated with a specific |
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space allocated to a particular logical processor, there will be data |
space allocated to a particular logical processor, there will be data |
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structures (arrays, scalar variables etc...) that hold the simulated state of |
structures (arrays, scalar variables etc...) that hold the simulated state of |
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that region. We refer to these data structures as being {\bf owned} by the |
that region. We refer to these data structures as being {\bf owned} by the |
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pprocessor to which their |
processor to which their |
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associated region of physical space has been allocated. Individual |
associated region of physical space has been allocated. Individual |
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regions that are allocated to processors are called {\bf tiles}. A |
regions that are allocated to processors are called {\bf tiles}. A |
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processor can own more |
processor can own more |
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whenever it requires values that outside the domain it owns. Periodically |
whenever it requires values that outside the domain it owns. Periodically |
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processors will make calls to WRAPPER functions to communicate data between |
processors will make calls to WRAPPER functions to communicate data between |
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tiles, in order to keep the overlap regions up to date (see section |
tiles, in order to keep the overlap regions up to date (see section |
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\ref{sec:communication_primitives}). The WRAPPER functions can use a |
\ref{sect:communication_primitives}). The WRAPPER functions can use a |
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variety of different mechanisms to communicate data between tiles. |
variety of different mechanisms to communicate data between tiles. |
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\begin{figure} |
\begin{figure} |
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\end{figure} |
\end{figure} |
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\subsection{Shared memory communication} |
\subsection{Shared memory communication} |
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\label{sec:shared_memory_communication} |
\label{sect:shared_memory_communication} |
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Under shared communication independent CPU's are operating |
Under shared communication independent CPU's are operating |
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on the exact same global address space at the application level. |
on the exact same global address space at the application level. |
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communication very efficient provided it is used appropriately. |
communication very efficient provided it is used appropriately. |
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\subsubsection{Memory consistency} |
\subsubsection{Memory consistency} |
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\label{sec:memory_consistency} |
\label{sect:memory_consistency} |
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When using shared memory communication between |
When using shared memory communication between |
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multiple processors the WRAPPER level shields user applications from |
multiple processors the WRAPPER level shields user applications from |
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ensure memory consistency for a particular platform. |
ensure memory consistency for a particular platform. |
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\subsubsection{Cache effects and false sharing} |
\subsubsection{Cache effects and false sharing} |
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\label{sec:cache_effects_and_false_sharing} |
\label{sect:cache_effects_and_false_sharing} |
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Shared-memory machines often have local to processor memory caches |
Shared-memory machines often have local to processor memory caches |
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which contain mirrored copies of main memory. Automatic cache-coherence |
which contain mirrored copies of main memory. Automatic cache-coherence |
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threads operating within a single process is the standard mechanism for |
threads operating within a single process is the standard mechanism for |
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supporting shared memory that the WRAPPER utilizes. Configuring and launching |
supporting shared memory that the WRAPPER utilizes. Configuring and launching |
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code to run in multi-threaded mode on specific platforms is discussed in |
code to run in multi-threaded mode on specific platforms is discussed in |
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section \ref{sec:running_with_threads}. However, on many systems, potentially |
section \ref{sect:running_with_threads}. However, on many systems, potentially |
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very efficient mechanisms for using shared memory communication between |
very efficient mechanisms for using shared memory communication between |
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multiple processes (in contrast to multiple threads within a single |
multiple processes (in contrast to multiple threads within a single |
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process) also exist. In most cases this works by making a limited region of |
process) also exist. In most cases this works by making a limited region of |
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nature. |
nature. |
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\subsection{Distributed memory communication} |
\subsection{Distributed memory communication} |
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\label{sec:distributed_memory_communication} |
\label{sect:distributed_memory_communication} |
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Many parallel systems are not constructed in a way where it is |
Many parallel systems are not constructed in a way where it is |
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possible or practical for an application to use shared memory |
possible or practical for an application to use shared memory |
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for communication. For example cluster systems consist of individual computers |
for communication. For example cluster systems consist of individual computers |
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highly optimized library. |
highly optimized library. |
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\subsection{Communication primitives} |
\subsection{Communication primitives} |
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\label{sec:communication_primitives} |
\label{sect:communication_primitives} |
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\begin{figure} |
\begin{figure} |
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\begin{center} |
\begin{center} |
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\includegraphics{part4/comm-primm.eps} |
\includegraphics{part4/comm-primm.eps} |
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} |
} |
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\end{center} |
\end{center} |
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\caption{Three performance critical parallel primititives are provided |
\caption{Three performance critical parallel primitives are provided |
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by the WRAPPER. These primititives are always used to communicate data |
by the WRAPPER. These primitives are always used to communicate data |
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between tiles. The figure shows four tiles. The curved arrows indicate |
between tiles. The figure shows four tiles. The curved arrows indicate |
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exchange primitives which transfer data between the overlap regions at tile |
exchange primitives which transfer data between the overlap regions at tile |
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edges and interior regions for nearest-neighbor tiles. |
edges and interior regions for nearest-neighbor tiles. |
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computing CPU's. |
computing CPU's. |
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\end{enumerate} |
\end{enumerate} |
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This section describes the details of each of these operations. |
This section describes the details of each of these operations. |
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Section \ref{sec:specifying_a_decomposition} explains how the way in which |
Section \ref{sect:specifying_a_decomposition} explains how the way in which |
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a domain is decomposed (or composed) is expressed. Section |
a domain is decomposed (or composed) is expressed. Section |
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\ref{sec:starting_a_code} describes practical details of running codes |
\ref{sect:starting_a_code} describes practical details of running codes |
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in various different parallel modes on contemporary computer systems. |
in various different parallel modes on contemporary computer systems. |
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Section \ref{sec:controlling_communication} explains the internal information |
Section \ref{sect:controlling_communication} explains the internal information |
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that the WRAPPER uses to control how information is communicated between |
that the WRAPPER uses to control how information is communicated between |
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tiles. |
tiles. |
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|
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\subsection{Specifying a domain decomposition} |
\subsection{Specifying a domain decomposition} |
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\label{sec:specifying_a_decomposition} |
\label{sect:specifying_a_decomposition} |
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At its heart much of the WRAPPER works only in terms of a collection of tiles |
At its heart much of the WRAPPER works only in terms of a collection of tiles |
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which are interconnected to each other. This is also true of application |
which are interconnected to each other. This is also true of application |
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dimensions of {\em sNx} and {\em sNy}. If, when the code is executed, these tiles are |
dimensions of {\em sNx} and {\em sNy}. If, when the code is executed, these tiles are |
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allocated to different threads of a process that are then bound to |
allocated to different threads of a process that are then bound to |
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different physical processors ( see the multi-threaded |
different physical processors ( see the multi-threaded |
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execution discussion in section \ref{sec:starting_the_code} ) then |
execution discussion in section \ref{sect:starting_the_code} ) then |
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computation will be performed concurrently on each tile. However, it is also |
computation will be performed concurrently on each tile. However, it is also |
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possible to run the same decomposition within a process running a single thread on |
possible to run the same decomposition within a process running a single thread on |
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a single processor. In this case the tiles will be computed over sequentially. |
a single processor. In this case the tiles will be computed over sequentially. |
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There are six tiles allocated to six separate logical processors ({\em nSx=6}). |
There are six tiles allocated to six separate logical processors ({\em nSx=6}). |
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This set of values can be used for a cube sphere calculation. |
This set of values can be used for a cube sphere calculation. |
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Each tile of size $32 \times 32$ represents a face of the |
Each tile of size $32 \times 32$ represents a face of the |
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cube. Initialising the tile connectivity correctly ( see section |
cube. Initializing the tile connectivity correctly ( see section |
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\ref{sec:cube_sphere_communication}. allows the rotations associated with |
\ref{sect:cube_sphere_communication}. allows the rotations associated with |
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moving between the six cube faces to be embedded within the |
moving between the six cube faces to be embedded within the |
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tile-tile communication code. |
tile-tile communication code. |
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\end{enumerate} |
\end{enumerate} |
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\subsection{Starting the code} |
\subsection{Starting the code} |
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\label{sec:starting_the_code} |
\label{sect:starting_the_code} |
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When code is started under the WRAPPER, execution begins in a main routine {\em |
When code is started under the WRAPPER, execution begins in a main routine {\em |
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eesupp/src/main.F} that is owned by the WRAPPER. Control is transferred |
eesupp/src/main.F} that is owned by the WRAPPER. Control is transferred |
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to the application through a routine called {\em THE\_MODEL\_MAIN()} |
to the application through a routine called {\em THE\_MODEL\_MAIN()} |
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WRAPPER is shown in figure \ref{fig:wrapper_startup}. |
WRAPPER is shown in figure \ref{fig:wrapper_startup}. |
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\begin{figure} |
\begin{figure} |
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|
{\footnotesize |
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\begin{verbatim} |
\begin{verbatim} |
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MAIN |
MAIN |
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\end{verbatim} |
\end{verbatim} |
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} |
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\caption{Main stages of the WRAPPER startup procedure. |
\caption{Main stages of the WRAPPER startup procedure. |
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This process proceeds transfer of control to application code, which |
This process proceeds transfer of control to application code, which |
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occurs through the procedure {\em THE\_MODEL\_MAIN()}. |
occurs through the procedure {\em THE\_MODEL\_MAIN()}. |
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\end{figure} |
\end{figure} |
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\subsubsection{Multi-threaded execution} |
\subsubsection{Multi-threaded execution} |
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\label{sect:multi-threaded-execution} |
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Prior to transferring control to the procedure {\em THE\_MODEL\_MAIN()} the |
Prior to transferring control to the procedure {\em THE\_MODEL\_MAIN()} the |
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WRAPPER may cause several coarse grain threads to be initialized. The routine |
WRAPPER may cause several coarse grain threads to be initialized. The routine |
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{\em THE\_MODEL\_MAIN()} is called once for each thread and is passed a single |
{\em THE\_MODEL\_MAIN()} is called once for each thread and is passed a single |
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stack argument which is the thread number, stored in the |
stack argument which is the thread number, stored in the |
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variable {\em myThid}. In addition to specifying a decomposition with |
variable {\em myThid}. In addition to specifying a decomposition with |
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multiple tiles per process ( see section \ref{sec:specifying_a_decomposition}) |
multiple tiles per process ( see section \ref{sect:specifying_a_decomposition}) |
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configuring and starting a code to run using multiple threads requires the following |
configuring and starting a code to run using multiple threads requires the following |
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steps.\\ |
steps.\\ |
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} \\ |
} \\ |
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\subsubsection{Multi-process execution} |
\subsubsection{Multi-process execution} |
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|
\label{sect:multi-process-execution} |
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|
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Despite its appealing programming model, multi-threaded execution remains |
Despite its appealing programming model, multi-threaded execution remains |
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less common then multi-process execution. One major reason for this |
less common then multi-process execution. One major reason for this |
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|
|
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Multi-process execution is more ubiquitous. |
Multi-process execution is more ubiquitous. |
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In order to run code in a multi-process configuration a decomposition |
In order to run code in a multi-process configuration a decomposition |
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specification is given ( in which the at least one of the |
specification ( see section \ref{sect:specifying_a_decomposition}) |
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|
is given ( in which the at least one of the |
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parameters {\em nPx} or {\em nPy} will be greater than one) |
parameters {\em nPx} or {\em nPy} will be greater than one) |
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and then, as for multi-threaded operation, |
and then, as for multi-threaded operation, |
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appropriate compile time and run time steps must be taken. |
appropriate compile time and run time steps must be taken. |
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\begin{verbatim} |
\begin{verbatim} |
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mpirun -np 64 -machinefile mf ./mitgcmuv |
mpirun -np 64 -machinefile mf ./mitgcmuv |
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\end{verbatim} |
\end{verbatim} |
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In this example the text {\em -np 64} specifices the number of processes |
In this example the text {\em -np 64} specifies the number of processes |
| 1022 |
that will be created. The numeric value {\em 64} must be equal to the |
that will be created. The numeric value {\em 64} must be equal to the |
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product of the processor grid settings of {\em nPx} and {\em nPy} |
product of the processor grid settings of {\em nPx} and {\em nPy} |
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in the file {\em SIZE.h}. The parameter {\em mf} specifies that a text file |
in the file {\em SIZE.h}. The parameter {\em mf} specifies that a text file |
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This latter set of variables can take one of the following values |
This latter set of variables can take one of the following values |
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{\em COMM\_NONE}, {\em COMM\_MSG}, {\em COMM\_PUT} and {\em COMM\_GET}. |
{\em COMM\_NONE}, {\em COMM\_MSG}, {\em COMM\_PUT} and {\em COMM\_GET}. |
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A value of {\em COMM\_NONE} is used to indicate that a tile has no |
A value of {\em COMM\_NONE} is used to indicate that a tile has no |
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neighbor to cummnicate with on a particular face. A value |
neighbor to communicate with on a particular face. A value |
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of {\em COMM\_MSG} is used to indicated that some form of distributed |
of {\em COMM\_MSG} is used to indicated that some form of distributed |
| 1126 |
memory communication is required to communicate between |
memory communication is required to communicate between |
| 1127 |
these tile faces ( see section \ref{sec:distributed_memory_communication}). |
these tile faces ( see section \ref{sect:distributed_memory_communication}). |
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A value of {\em COMM\_PUT} or {\em COMM\_GET} is used to indicate |
A value of {\em COMM\_PUT} or {\em COMM\_GET} is used to indicate |
| 1129 |
forms of shared memory communication ( see section |
forms of shared memory communication ( see section |
| 1130 |
\ref{sec:shared_memory_communication}). The {\em COMM\_PUT} value indicates |
\ref{sect:shared_memory_communication}). The {\em COMM\_PUT} value indicates |
| 1131 |
that a CPU should communicate by writing to data structures owned by another |
that a CPU should communicate by writing to data structures owned by another |
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CPU. A {\em COMM\_GET} value indicates that a CPU should communicate by reading |
CPU. A {\em COMM\_GET} value indicates that a CPU should communicate by reading |
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from data structures owned by another CPU. These flags affect the behavior |
from data structures owned by another CPU. These flags affect the behavior |
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are read from the file {\em eedata}. If the value of {\em nThreads} |
are read from the file {\em eedata}. If the value of {\em nThreads} |
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is inconsistent with the number of threads requested from the |
is inconsistent with the number of threads requested from the |
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operating system (for example by using an environment |
operating system (for example by using an environment |
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varialble as described in section \ref{sec:multi_threaded_execution}) |
variable as described in section \ref{sect:multi_threaded_execution}) |
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then usually an error will be reported by the routine |
then usually an error will be reported by the routine |
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{\em CHECK\_THREADS}.\\ |
{\em CHECK\_THREADS}.\\ |
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|
|
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} |
} |
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|
|
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\item {\bf memsync flags} |
\item {\bf memsync flags} |
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As discussed in section \ref{sec:memory_consistency}, when using shared memory, |
As discussed in section \ref{sect:memory_consistency}, when using shared memory, |
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a low-level system function may be need to force memory consistency. |
a low-level system function may be need to force memory consistency. |
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The routine {\em MEMSYNC()} is used for this purpose. This routine should |
The routine {\em MEMSYNC()} is used for this purpose. This routine should |
| 1202 |
not need modifying and the information below is only provided for |
not need modifying and the information below is only provided for |
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\begin{verbatim} |
\begin{verbatim} |
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asm("membar #LoadStore|#StoreStore"); |
asm("membar #LoadStore|#StoreStore"); |
| 1214 |
\end{verbatim} |
\end{verbatim} |
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for an Alpha based sytem the euivalent code reads |
for an Alpha based system the equivalent code reads |
| 1216 |
\begin{verbatim} |
\begin{verbatim} |
| 1217 |
asm("mb"); |
asm("mb"); |
| 1218 |
\end{verbatim} |
\end{verbatim} |
| 1222 |
\end{verbatim} |
\end{verbatim} |
| 1223 |
|
|
| 1224 |
\item {\bf Cache line size} |
\item {\bf Cache line size} |
| 1225 |
As discussed in section \ref{sec:cache_effects_and_false_sharing}, |
As discussed in section \ref{sect:cache_effects_and_false_sharing}, |
| 1226 |
milti-threaded codes explicitly avoid penalties associated with excessive |
milti-threaded codes explicitly avoid penalties associated with excessive |
| 1227 |
coherence traffic on an SMP system. To do this the sgared memory data structures |
coherence traffic on an SMP system. To do this the shared memory data structures |
| 1228 |
used by the {\em GLOBAL\_SUM}, {\em GLOBAL\_MAX} and {\em BARRIER} routines |
used by the {\em GLOBAL\_SUM}, {\em GLOBAL\_MAX} and {\em BARRIER} routines |
| 1229 |
are padded. The variables that control the padding are set in the |
are padded. The variables that control the padding are set in the |
| 1230 |
header file {\em EEPARAMS.h}. These variables are called |
header file {\em EEPARAMS.h}. These variables are called |
| 1232 |
{\em lShare8}. The default values should not normally need changing. |
{\em lShare8}. The default values should not normally need changing. |
| 1233 |
\item {\bf \_BARRIER} |
\item {\bf \_BARRIER} |
| 1234 |
This is a CPP macro that is expanded to a call to a routine |
This is a CPP macro that is expanded to a call to a routine |
| 1235 |
which synchronises all the logical processors running under the |
which synchronizes all the logical processors running under the |
| 1236 |
WRAPPER. Using a macro here preserves flexibility to insert |
WRAPPER. Using a macro here preserves flexibility to insert |
| 1237 |
a specialized call in-line into application code. By default this |
a specialized call in-line into application code. By default this |
| 1238 |
resolves to calling the procedure {\em BARRIER()}. The default |
resolves to calling the procedure {\em BARRIER()}. The default |
| 1240 |
|
|
| 1241 |
\item {\bf \_GSUM} |
\item {\bf \_GSUM} |
| 1242 |
This is a CPP macro that is expanded to a call to a routine |
This is a CPP macro that is expanded to a call to a routine |
| 1243 |
which sums up a floating point numner |
which sums up a floating point number |
| 1244 |
over all the logical processors running under the |
over all the logical processors running under the |
| 1245 |
WRAPPER. Using a macro here provides extra flexibility to insert |
WRAPPER. Using a macro here provides extra flexibility to insert |
| 1246 |
a specialized call in-line into application code. By default this |
a specialized call in-line into application code. By default this |
| 1247 |
resolves to calling the procedure {\em GLOBAL\_SOM\_R8()} ( for |
resolves to calling the procedure {\em GLOBAL\_SUM\_R8()} ( for |
| 1248 |
84=bit floating point operands) |
64-bit floating point operands) |
| 1249 |
or {\em GLOBAL\_SOM\_R4()} (for 32-bit floating point operands). The default |
or {\em GLOBAL\_SUM\_R4()} (for 32-bit floating point operands). The default |
| 1250 |
setting for the \_GSUM macro is given in the file {\em CPP\_EEMACROS.h}. |
setting for the \_GSUM macro is given in the file {\em CPP\_EEMACROS.h}. |
| 1251 |
The \_GSUM macro is a performance critical operation, especially for |
The \_GSUM macro is a performance critical operation, especially for |
| 1252 |
large processor count, small tile size configurations. |
large processor count, small tile size configurations. |
| 1253 |
The custom communication example discussed in section \ref{sec:jam_example} |
The custom communication example discussed in section \ref{sect:jam_example} |
| 1254 |
shows how the macro is used to invoke a custom global sum routine |
shows how the macro is used to invoke a custom global sum routine |
| 1255 |
for a specific set of hardware. |
for a specific set of hardware. |
| 1256 |
|
|
| 1264 |
in the header file {\em CPP\_EEMACROS.h}. As with \_GSUM, the |
in the header file {\em CPP\_EEMACROS.h}. As with \_GSUM, the |
| 1265 |
\_EXCH operation plays a crucial role in scaling to small tile, |
\_EXCH operation plays a crucial role in scaling to small tile, |
| 1266 |
large logical and physical processor count configurations. |
large logical and physical processor count configurations. |
| 1267 |
The example in section \ref{sec:jam_example} discusses defining an |
The example in section \ref{sect:jam_example} discusses defining an |
| 1268 |
optimised and specialized form on the \_EXCH operation. |
optimized and specialized form on the \_EXCH operation. |
| 1269 |
|
|
| 1270 |
The \_EXCH operation is also central to supporting grids such as |
The \_EXCH operation is also central to supporting grids such as |
| 1271 |
the cube-sphere grid. In this class of grid a rotation may be required |
the cube-sphere grid. In this class of grid a rotation may be required |
| 1272 |
between tiles. Aligning the coordinate requiring rotation with the |
between tiles. Aligning the coordinate requiring rotation with the |
| 1273 |
tile decomposistion, allows the coordinate transformation to |
tile decomposition, allows the coordinate transformation to |
| 1274 |
be embedded within a custom form of the \_EXCH primitive. |
be embedded within a custom form of the \_EXCH primitive. |
| 1275 |
|
|
| 1276 |
\item {\bf Reverse Mode} |
\item {\bf Reverse Mode} |
| 1277 |
The communication primitives \_EXCH and \_GSUM both employ |
The communication primitives \_EXCH and \_GSUM both employ |
| 1278 |
hand-written adjoint forms (or reverse mode) forms. |
hand-written adjoint forms (or reverse mode) forms. |
| 1279 |
These reverse mode forms can be found in the |
These reverse mode forms can be found in the |
| 1280 |
sourc code directory {\em pkg/autodiff}. |
source code directory {\em pkg/autodiff}. |
| 1281 |
For the global sum primitive the reverse mode form |
For the global sum primitive the reverse mode form |
| 1282 |
calls are to {\em GLOBAL\_ADSUM\_R4} and |
calls are to {\em GLOBAL\_ADSUM\_R4} and |
| 1283 |
{\em GLOBAL\_ADSUM\_R8}. The reverse mode form of the |
{\em GLOBAL\_ADSUM\_R8}. The reverse mode form of the |
| 1284 |
exchamge primitives are found in routines |
exchange primitives are found in routines |
| 1285 |
prefixed {\em ADEXCH}. The exchange routines make calls to |
prefixed {\em ADEXCH}. The exchange routines make calls to |
| 1286 |
the same low-level communication primitives as the forward mode |
the same low-level communication primitives as the forward mode |
| 1287 |
operations. However, the routine argument {\em simulationMode} |
operations. However, the routine argument {\em simulationMode} |
| 1293 |
maximum number of OS threads that a code will use. This |
maximum number of OS threads that a code will use. This |
| 1294 |
value defaults to thirty-two and is set in the file {\em EEPARAMS.h}. |
value defaults to thirty-two and is set in the file {\em EEPARAMS.h}. |
| 1295 |
For single threaded execution it can be reduced to one if required. |
For single threaded execution it can be reduced to one if required. |
| 1296 |
The va;lue is largely private to the WRAPPER and application code |
The value; is largely private to the WRAPPER and application code |
| 1297 |
will nor normally reference the value, except in the following scenario. |
will nor normally reference the value, except in the following scenario. |
| 1298 |
|
|
| 1299 |
For certain physical parametrization schemes it is necessary to have |
For certain physical parametrization schemes it is necessary to have |
| 1304 |
if this might be unavailable then the work arrays can be extended |
if this might be unavailable then the work arrays can be extended |
| 1305 |
with dimensions use the tile dimensioning scheme of {\em nSx} |
with dimensions use the tile dimensioning scheme of {\em nSx} |
| 1306 |
and {\em nSy} ( as described in section |
and {\em nSy} ( as described in section |
| 1307 |
\ref{sec:specifying_a_decomposition}). However, if the configuration |
\ref{sect:specifying_a_decomposition}). However, if the configuration |
| 1308 |
being specified involves many more tiles than OS threads then |
being specified involves many more tiles than OS threads then |
| 1309 |
it can save memory resources to reduce the variable |
it can save memory resources to reduce the variable |
| 1310 |
{\em MAX\_NO\_THREADS} to be equal to the actual number of threads that |
{\em MAX\_NO\_THREADS} to be equal to the actual number of threads that |
| 1311 |
will be used and to declare the physical parameterisation |
will be used and to declare the physical parameterization |
| 1312 |
work arrays with a sinble {\em MAX\_NO\_THREADS} extra dimension. |
work arrays with a single {\em MAX\_NO\_THREADS} extra dimension. |
| 1313 |
An example of this is given in the verification experiment |
An example of this is given in the verification experiment |
| 1314 |
{\em aim.5l\_cs}. Here the default setting of |
{\em aim.5l\_cs}. Here the default setting of |
| 1315 |
{\em MAX\_NO\_THREADS} is altered to |
{\em MAX\_NO\_THREADS} is altered to |
| 1322 |
\begin{verbatim} |
\begin{verbatim} |
| 1323 |
common /FORCIN/ sst1(ngp,MAX_NO_THREADS) |
common /FORCIN/ sst1(ngp,MAX_NO_THREADS) |
| 1324 |
\end{verbatim} |
\end{verbatim} |
| 1325 |
This declaration scheme is not used widely, becuase most global data |
This declaration scheme is not used widely, because most global data |
| 1326 |
is used for permanent not temporary storage of state information. |
is used for permanent not temporary storage of state information. |
| 1327 |
In the case of permanent state information this approach cannot be used |
In the case of permanent state information this approach cannot be used |
| 1328 |
because there has to be enough storage allocated for all tiles. |
because there has to be enough storage allocated for all tiles. |
| 1329 |
However, the technique can sometimes be a useful scheme for reducing memory |
However, the technique can sometimes be a useful scheme for reducing memory |
| 1330 |
requirements in complex physical paramterisations. |
requirements in complex physical parameterizations. |
| 1331 |
\end{enumerate} |
\end{enumerate} |
| 1332 |
|
|
| 1333 |
\begin{figure} |
\begin{figure} |
| 1360 |
The isolation of performance critical communication primitives and the |
The isolation of performance critical communication primitives and the |
| 1361 |
sub-division of the simulation domain into tiles is a powerful tool. |
sub-division of the simulation domain into tiles is a powerful tool. |
| 1362 |
Here we show how it can be used to improve application performance and |
Here we show how it can be used to improve application performance and |
| 1363 |
how it can be used to adapt to new gridding approaches. |
how it can be used to adapt to new griding approaches. |
| 1364 |
|
|
| 1365 |
\subsubsection{JAM example} |
\subsubsection{JAM example} |
| 1366 |
\label{sec:jam_example} |
\label{sect:jam_example} |
| 1367 |
On some platforms a big performance boost can be obtained by |
On some platforms a big performance boost can be obtained by |
| 1368 |
binding the communication routines {\em \_EXCH} and |
binding the communication routines {\em \_EXCH} and |
| 1369 |
{\em \_GSUM} to specialized native libraries ) fro example the |
{\em \_GSUM} to specialized native libraries ) fro example the |
| 1379 |
\item The {\em \_GSUM} and {\em \_EXCH} macro definitions are replaced |
\item The {\em \_GSUM} and {\em \_EXCH} macro definitions are replaced |
| 1380 |
with calls to custom routines ( see {\em gsum\_jam.F} and {\em exch\_jam.F}) |
with calls to custom routines ( see {\em gsum\_jam.F} and {\em exch\_jam.F}) |
| 1381 |
\item a highly specialized form of the exchange operator (optimized |
\item a highly specialized form of the exchange operator (optimized |
| 1382 |
for overlap regions of width one) is substitued into the elliptic |
for overlap regions of width one) is substituted into the elliptic |
| 1383 |
solver routine {\em cg2d.F}. |
solver routine {\em cg2d.F}. |
| 1384 |
\end{itemize} |
\end{itemize} |
| 1385 |
Developing specialized code for other libraries follows a similar |
Developing specialized code for other libraries follows a similar |
| 1386 |
pattern. |
pattern. |
| 1387 |
|
|
| 1388 |
\subsubsection{Cube sphere communication} |
\subsubsection{Cube sphere communication} |
| 1389 |
\label{sec:cube_sphere_communication} |
\label{sect:cube_sphere_communication} |
| 1390 |
Actual {\em \_EXCH} routine code is generated automatically from |
Actual {\em \_EXCH} routine code is generated automatically from |
| 1391 |
a series of template files, for example {\em exch\_rx.template}. |
a series of template files, for example {\em exch\_rx.template}. |
| 1392 |
This is done to allow a large number of variations on the exchange |
This is done to allow a large number of variations on the exchange |
| 1393 |
process to be maintained. One set of variations supports the |
process to be maintained. One set of variations supports the |
| 1394 |
cube sphere grid. Support for a cube sphere gris in MITgcm is based |
cube sphere grid. Support for a cube sphere grid in MITgcm is based |
| 1395 |
on having each face of the cube as a separate tile (or tiles). |
on having each face of the cube as a separate tile (or tiles). |
| 1396 |
The exchage routines are then able to absorb much of the |
The exchange routines are then able to absorb much of the |
| 1397 |
detailed rotation and reorientation required when moving around the |
detailed rotation and reorientation required when moving around the |
| 1398 |
cube grid. The set of {\em \_EXCH} routines that contain the |
cube grid. The set of {\em \_EXCH} routines that contain the |
| 1399 |
word cube in their name perform these transformations. |
word cube in their name perform these transformations. |
| 1400 |
They are invoked when the run-time logical parameter |
They are invoked when the run-time logical parameter |
| 1401 |
{\em useCubedSphereExchange} is set true. To facilitate the |
{\em useCubedSphereExchange} is set true. To facilitate the |
| 1402 |
transformations on a staggered C-grid, exchange operations are defined |
transformations on a staggered C-grid, exchange operations are defined |
| 1403 |
separately for both vector and scalar quantitities and for |
separately for both vector and scalar quantities and for |
| 1404 |
grid-centered and for grid-face and corner quantities. |
grid-centered and for grid-face and corner quantities. |
| 1405 |
Three sets of exchange routines are defined. Routines |
Three sets of exchange routines are defined. Routines |
| 1406 |
with names of the form {\em exch\_rx} are used to exchange |
with names of the form {\em exch\_rx} are used to exchange |
| 1419 |
|
|
| 1420 |
Fitting together the WRAPPER elements, package elements and |
Fitting together the WRAPPER elements, package elements and |
| 1421 |
MITgcm core equation elements of the source code produces calling |
MITgcm core equation elements of the source code produces calling |
| 1422 |
sequence shown in section \ref{sec:calling_sequence} |
sequence shown in section \ref{sect:calling_sequence} |
| 1423 |
|
|
| 1424 |
\subsection{Annotated call tree for MITgcm and WRAPPER} |
\subsection{Annotated call tree for MITgcm and WRAPPER} |
| 1425 |
\label{sec:calling_sequence} |
\label{sect:calling_sequence} |
| 1426 |
|
|
| 1427 |
WRAPPER layer. |
WRAPPER layer. |
| 1428 |
|
|
| 1429 |
|
{\footnotesize |
| 1430 |
\begin{verbatim} |
\begin{verbatim} |
| 1431 |
|
|
| 1432 |
MAIN |
MAIN |
| 1454 |
|--THE_MODEL_MAIN :: Numerical code top-level driver routine |
|--THE_MODEL_MAIN :: Numerical code top-level driver routine |
| 1455 |
|
|
| 1456 |
\end{verbatim} |
\end{verbatim} |
| 1457 |
|
} |
| 1458 |
|
|
| 1459 |
Core equations plus packages. |
Core equations plus packages. |
| 1460 |
|
|
| 1461 |
|
{\footnotesize |
| 1462 |
\begin{verbatim} |
\begin{verbatim} |
| 1463 |
C |
C |
| 1464 |
C |
C |
| 1468 |
C | |
C | |
| 1469 |
C |-THE_MODEL_MAIN :: Primary driver for the MITgcm algorithm |
C |-THE_MODEL_MAIN :: Primary driver for the MITgcm algorithm |
| 1470 |
C | :: Called from WRAPPER level numerical |
C | :: Called from WRAPPER level numerical |
| 1471 |
C | :: code innvocation routine. On entry |
C | :: code invocation routine. On entry |
| 1472 |
C | :: to THE_MODEL_MAIN separate thread and |
C | :: to THE_MODEL_MAIN separate thread and |
| 1473 |
C | :: separate processes will have been established. |
C | :: separate processes will have been established. |
| 1474 |
C | :: Each thread and process will have a unique ID |
C | :: Each thread and process will have a unique ID |
| 1482 |
C | | :: By default kernel parameters are read from file |
C | | :: By default kernel parameters are read from file |
| 1483 |
C | | :: "data" in directory in which code executes. |
C | | :: "data" in directory in which code executes. |
| 1484 |
C | | |
C | | |
| 1485 |
C | |-MON_INIT :: Initialises monitor pacakge ( see pkg/monitor ) |
C | |-MON_INIT :: Initializes monitor package ( see pkg/monitor ) |
| 1486 |
C | | |
C | | |
| 1487 |
C | |-INI_GRID :: Control grid array (vert. and hori.) initialisation. |
C | |-INI_GRID :: Control grid array (vert. and hori.) initialization. |
| 1488 |
C | | | :: Grid arrays are held and described in GRID.h. |
C | | | :: Grid arrays are held and described in GRID.h. |
| 1489 |
C | | | |
C | | | |
| 1490 |
C | | |-INI_VERTICAL_GRID :: Initialise vertical grid arrays. |
C | | |-INI_VERTICAL_GRID :: Initialize vertical grid arrays. |
| 1491 |
C | | | |
C | | | |
| 1492 |
C | | |-INI_CARTESIAN_GRID :: Cartesian horiz. grid initialisation |
C | | |-INI_CARTESIAN_GRID :: Cartesian horiz. grid initialization |
| 1493 |
C | | | :: (calculate grid from kernel parameters). |
C | | | :: (calculate grid from kernel parameters). |
| 1494 |
C | | | |
C | | | |
| 1495 |
C | | |-INI_SPHERICAL_POLAR_GRID :: Spherical polar horiz. grid |
C | | |-INI_SPHERICAL_POLAR_GRID :: Spherical polar horiz. grid |
| 1496 |
C | | | :: initialisation (calculate grid from |
C | | | :: initialization (calculate grid from |
| 1497 |
C | | | :: kernel parameters). |
C | | | :: kernel parameters). |
| 1498 |
C | | | |
C | | | |
| 1499 |
C | | |-INI_CURVILINEAR_GRID :: General orthogonal, structured horiz. |
C | | |-INI_CURVILINEAR_GRID :: General orthogonal, structured horiz. |
| 1500 |
C | | :: grid initialisations. ( input from raw |
C | | :: grid initializations. ( input from raw |
| 1501 |
C | | :: grid files, LONC.bin, DXF.bin etc... ) |
C | | :: grid files, LONC.bin, DXF.bin etc... ) |
| 1502 |
C | | |
C | | |
| 1503 |
C | |-INI_DEPTHS :: Read (from "bathyFile") or set bathymetry/orgography. |
C | |-INI_DEPTHS :: Read (from "bathyFile") or set bathymetry/orgography. |
| 1508 |
C | |-INI_LINEAR_PHSURF :: Set ref. surface Bo_surf |
C | |-INI_LINEAR_PHSURF :: Set ref. surface Bo_surf |
| 1509 |
C | | |
C | | |
| 1510 |
C | |-INI_CORI :: Set coriolis term. zero, f-plane, beta-plane, |
C | |-INI_CORI :: Set coriolis term. zero, f-plane, beta-plane, |
| 1511 |
C | | :: sphere optins are coded. |
C | | :: sphere options are coded. |
| 1512 |
C | | |
C | | |
| 1513 |
C | |-PACAKGES_BOOT :: Start up the optional package environment. |
C | |-PACAKGES_BOOT :: Start up the optional package environment. |
| 1514 |
C | | :: Runtime selection of active packages. |
C | | :: Runtime selection of active packages. |
| 1529 |
C | |-PACKAGES_CHECK |
C | |-PACKAGES_CHECK |
| 1530 |
C | | | |
C | | | |
| 1531 |
C | | |-KPP_CHECK :: KPP Package. pkg/kpp |
C | | |-KPP_CHECK :: KPP Package. pkg/kpp |
| 1532 |
C | | |-OBCS_CHECK :: Open bndy Pacakge. pkg/obcs |
C | | |-OBCS_CHECK :: Open bndy Package. pkg/obcs |
| 1533 |
C | | |-GMREDI_CHECK :: GM Package. pkg/gmredi |
C | | |-GMREDI_CHECK :: GM Package. pkg/gmredi |
| 1534 |
C | | |
C | | |
| 1535 |
C | |-PACKAGES_INIT_FIXED |
C | |-PACKAGES_INIT_FIXED |
| 1549 |
C |-CTRL_UNPACK :: Control vector support package. see pkg/ctrl |
C |-CTRL_UNPACK :: Control vector support package. see pkg/ctrl |
| 1550 |
C | |
C | |
| 1551 |
C |-ADTHE_MAIN_LOOP :: Derivative evaluating form of main time stepping loop |
C |-ADTHE_MAIN_LOOP :: Derivative evaluating form of main time stepping loop |
| 1552 |
C ! :: Auotmatically gerenrated by TAMC/TAF. |
C ! :: Auotmatically generated by TAMC/TAF. |
| 1553 |
C | |
C | |
| 1554 |
C |-CTRL_PACK :: Control vector support package. see pkg/ctrl |
C |-CTRL_PACK :: Control vector support package. see pkg/ctrl |
| 1555 |
C | |
C | |
| 1563 |
C | | |-INI_LINEAR_PHISURF :: Set ref. surface Bo_surf |
C | | |-INI_LINEAR_PHISURF :: Set ref. surface Bo_surf |
| 1564 |
C | | | |
C | | | |
| 1565 |
C | | |-INI_CORI :: Set coriolis term. zero, f-plane, beta-plane, |
C | | |-INI_CORI :: Set coriolis term. zero, f-plane, beta-plane, |
| 1566 |
C | | | :: sphere optins are coded. |
C | | | :: sphere options are coded. |
| 1567 |
C | | | |
C | | | |
| 1568 |
C | | |-INI_CG2D :: 2d con. grad solver initialisation. |
C | | |-INI_CG2D :: 2d con. grad solver initialisation. |
| 1569 |
C | | |-INI_CG3D :: 3d con. grad solver initialisation. |
C | | |-INI_CG3D :: 3d con. grad solver initialisation. |
| 1571 |
C | | |-INI_DYNVARS :: Initialise to zero all DYNVARS.h arrays (dynamical |
C | | |-INI_DYNVARS :: Initialise to zero all DYNVARS.h arrays (dynamical |
| 1572 |
C | | | :: fields). |
C | | | :: fields). |
| 1573 |
C | | | |
C | | | |
| 1574 |
C | | |-INI_FIELDS :: Control initialising model fields to non-zero |
C | | |-INI_FIELDS :: Control initializing model fields to non-zero |
| 1575 |
C | | | |-INI_VEL :: Initialize 3D flow field. |
C | | | |-INI_VEL :: Initialize 3D flow field. |
| 1576 |
C | | | |-INI_THETA :: Set model initial temperature field. |
C | | | |-INI_THETA :: Set model initial temperature field. |
| 1577 |
C | | | |-INI_SALT :: Set model initial salinity field. |
C | | | |-INI_SALT :: Set model initial salinity field. |
| 1649 |
C/\ | | |-CALC_SURF_DR :: Calculate the new surface level thickness. |
C/\ | | |-CALC_SURF_DR :: Calculate the new surface level thickness. |
| 1650 |
C/\ | | |-EXF_GETFORCING :: External forcing package. ( pkg/exf ) |
C/\ | | |-EXF_GETFORCING :: External forcing package. ( pkg/exf ) |
| 1651 |
C/\ | | |-EXTERNAL_FIELDS_LOAD :: Control loading time dep. external data. |
C/\ | | |-EXTERNAL_FIELDS_LOAD :: Control loading time dep. external data. |
| 1652 |
C/\ | | | | :: Simple interpolcation between end-points |
C/\ | | | | :: Simple interpolation between end-points |
| 1653 |
C/\ | | | | :: for forcing datasets. |
C/\ | | | | :: for forcing datasets. |
| 1654 |
C/\ | | | | |
C/\ | | | | |
| 1655 |
C/\ | | | |-EXCH :: Sync forcing. in overlap regions. |
C/\ | | | |-EXCH :: Sync forcing. in overlap regions. |
| 1797 |
C :: events. |
C :: events. |
| 1798 |
C |
C |
| 1799 |
\end{verbatim} |
\end{verbatim} |
| 1800 |
|
} |
| 1801 |
|
|
| 1802 |
\subsection{Measuring and Characterizing Performance} |
\subsection{Measuring and Characterizing Performance} |
| 1803 |
|
|