10 |
%% o automatically inserted at \section{Reference} |
%% o automatically inserted at \section{Reference} |
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12 |
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13 |
\section{exch2: Extended Cubed Sphere Exchange} |
\section{exch2: Extended Cubed Sphere \mbox{Topology}} |
14 |
\label{sec:exch2} |
\label{sec:exch2} |
15 |
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16 |
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|
17 |
\subsection{Introduction} |
\subsection{Introduction} |
18 |
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|
19 |
The exch2 package is an extension to the original cubed sphere exchanges |
The \texttt{exch2} package extends the original cubed |
20 |
to allow more flexible domain decomposition and parallelization. Cube faces |
sphere topology configuration to allow more flexible domain |
21 |
(subdomains) may be divided into whatever number of tiles that divide evenly |
decomposition and parallelization. Cube faces (also called |
22 |
into the grid point dimensions of the subdomain. Furthermore, the individual |
subdomains) may be divided into any number of tiles that divide evenly |
23 |
tiles may be run on separate processors in different combinations, |
into the grid point dimensions of the subdomain. Furthermore, the |
24 |
and whether exchanges between particular tiles occur between different |
individual tiles can run on separate processors in different |
25 |
processors is determined at runtime. |
combinations, and whether exchanges between particular tiles occur |
26 |
|
between different processors is determined at runtime. This |
27 |
The exchange parameters are declared in {\em W2\_EXCH2\_TOPOLOGY.h} and |
flexibility provides for manual compile-time load balancing across a |
28 |
assigned in {\em w2\_e2setup.F}, both in the |
relatively arbitrary number of processors. \\ |
29 |
{\em pkg/exch2} directory. The validity of the cube topology depends |
|
30 |
on the {\em SIZE.h} file as detailed below. Both files are generated by |
The exchange parameters are declared in |
31 |
Matlab scripts and |
\filelink{pkg/exch2/W2\_EXCH2\_TOPOLOGY.h}{pkg-exch2-W2_EXCH2_TOPOLOGY.h} |
32 |
should not be edited. The default files provided in the release set up |
and assigned in |
33 |
a cube sphere arrangement of six tiles, one per subdomain, each with 32x32 grid |
\filelink{pkg/exch2/w2\_e2setup.F}{pkg-exch2-w2_e2setup.F}. The |
34 |
points, running on a single processor. |
validity of the cube topology depends on the \file{SIZE.h} file as |
35 |
|
detailed below. The default files provided in the release configure a |
36 |
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cubed sphere topology of six tiles, one per subdomain, each with |
37 |
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32$\times$32 grid points, all running on a single processor. Both |
38 |
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files are generated by Matlab scripts in |
39 |
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\file{utils/exch2/matlab-topology-generator}; see Section |
40 |
|
\ref{sec:topogen} \sectiontitle{Generating Topology Files for exch2} |
41 |
|
for details on creating alternate topologies. Pregenerated examples |
42 |
|
of these files with alternate topologies are provided under |
43 |
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\file{utils/exch2/code-mods} along with the appropriate \file{SIZE.h} |
44 |
|
file for single-processor execution. |
45 |
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|
46 |
|
\subsection{Invoking exch2} |
47 |
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|
48 |
|
To use exch2 with the cubed sphere, the following conditions must be |
49 |
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met: \\ |
50 |
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|
51 |
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$\bullet$ The exch2 package is included when \file{genmake2} is run. |
52 |
|
The easiest way to do this is to add the line \code{exch2} to the |
53 |
|
\file{profile.conf} file -- see Section |
54 |
|
\ref{sect:buildingCode} \sectiontitle{Building the code} for general |
55 |
|
details. \\ |
56 |
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|
57 |
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$\bullet$ An example of \file{W2\_EXCH2\_TOPOLOGY.h} and |
58 |
|
\file{w2\_e2setup.F} must reside in a directory containing code |
59 |
|
linked when \file{genmake2} runs. The safest place to put these |
60 |
|
is the directory indicated in the \code{-mods=DIR} command line |
61 |
|
modifier (typically \file{../code}), or the build directory. The |
62 |
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default versions of these files reside in \file{pkg/exch2} and are |
63 |
|
linked automatically if no other versions exist elsewhere in the |
64 |
|
link path, but they should be left untouched to avoid breaking |
65 |
|
configurations other than the one you intend to modify.\\ |
66 |
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|
67 |
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$\bullet$ Files containing grid parameters, named |
68 |
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\file{tile00$n$.mitgrid} where $n$=\code{(1:6)} (one per subdomain), |
69 |
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must be in the working directory when the MITgcm executable is run. |
70 |
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These files are provided in the example experiments for cubed sphere |
71 |
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configurations with 32$\times$32 cube sides and are non-trivial to |
72 |
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generate -- please contact MITgcm support if you want to generate |
73 |
|
files for other configurations. \\ |
74 |
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|
75 |
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$\bullet$ As always when compiling MITgcm, the file \file{SIZE.h} must |
76 |
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be placed where \file{genmake2} will find it. In particular for |
77 |
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exch2, the domain decomposition specified in \file{SIZE.h} must |
78 |
|
correspond with the particular configuration's topology specified in |
79 |
|
\file{W2\_EXCH2\_TOPOLOGY.h} and \file{w2\_e2setup.F}. Domain |
80 |
|
decomposition issues particular to exch2 are addressed in Section |
81 |
|
\ref{sec:topogen} \sectiontitle{Generating Topology Files for exch2} |
82 |
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and \ref{sec:exch2mpi} \sectiontitle{exch2, SIZE.h, and MPI}; a more |
83 |
|
general background on the subject relevant to MITgcm is presented in |
84 |
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Section \ref{sect:specifying_a_decomposition} |
85 |
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\sectiontitle{Specifying a decomposition}.\\ |
86 |
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|
87 |
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As of the time of writing the following examples use exch2 and may be |
88 |
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used for guidance: |
89 |
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|
90 |
|
\begin{verbatim} |
91 |
|
verification/adjust_nlfs.cs-32x32x1 |
92 |
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verification/adjustment.cs-32x32x1 |
93 |
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verification/aim.5l_cs |
94 |
|
verification/global_ocean.cs32x15 |
95 |
|
verification/hs94.cs-32x32x5 |
96 |
|
\end{verbatim} |
97 |
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|
98 |
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|
99 |
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|
100 |
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|
101 |
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\subsection{Generating Topology Files for exch2} |
102 |
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\label{sec:topogen} |
103 |
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|
104 |
|
Alternate cubed sphere topologies may be created using the Matlab |
105 |
|
scripts in \file{utils/exch2/matlab-topology-generator}. Running the |
106 |
|
m-file |
107 |
|
\filelink{driver.m}{utils-exch2-matlab-topology-generator_driver.m} |
108 |
|
from the Matlab prompt (there are no parameters to pass) generates |
109 |
|
exch2 topology files \file{W2\_EXCH2\_TOPOLOGY.h} and |
110 |
|
\file{w2\_e2setup.F} in the working directory and displays a figure of |
111 |
|
the topology via Matlab. The other m-files in the directory are |
112 |
|
subroutines of \file{driver.m} and should not be run ``bare'' except |
113 |
|
for development purposes. \\ |
114 |
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|
115 |
|
The parameters that determine the dimensions and topology of the |
116 |
|
generated configuration are \code{nr}, \code{nb}, \code{ng}, |
117 |
|
\code{tnx} and \code{tny}, and all are assigned early in the script. \\ |
118 |
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|
119 |
|
The first three determine the size of the subdomains and |
120 |
|
hence the size of the overall domain. Each one determines the number |
121 |
|
of grid points, and therefore the resolution, along the subdomain |
122 |
|
sides in a ``great circle'' around an axis of the cube. At the time |
123 |
|
of this writing MITgcm requires these three parameters to be equal, |
124 |
|
but they provide for future releases to accomodate different |
125 |
|
resolutions around the axes to allow (for example) greater resolution |
126 |
|
around the equator.\\ |
127 |
|
|
128 |
|
The parameters \code{tnx} and \code{tny} determine the dimensions of |
129 |
|
the tiles into which the subdomains are decomposed, and must evenly |
130 |
|
divide the integer assigned to \code{nr}, \code{nb} and \code{ng}. |
131 |
|
The result is a rectangular tiling of the subdomain. Figure |
132 |
|
\ref{fig:24tile} shows one possible topology for a twentyfour-tile |
133 |
|
cube, and figure \ref{fig:12tile} shows one for twelve tiles. \\ |
134 |
|
|
135 |
|
\begin{figure} |
136 |
|
\begin{center} |
137 |
|
\resizebox{4in}{!}{ |
138 |
|
\includegraphics{part6/s24t_16x16.ps} |
139 |
|
} |
140 |
|
\end{center} |
141 |
|
|
142 |
|
\caption{Plot of a cubed sphere topology with a 32$\times$192 domain |
143 |
|
divided into six 32$\times$32 subdomains, each of which is divided into four tiles |
144 |
|
(\code{tnx=16, tny=16}) for a total of twentyfour tiles. |
145 |
|
} \label{fig:24tile} |
146 |
|
\end{figure} |
147 |
|
|
148 |
|
\begin{figure} |
149 |
|
\begin{center} |
150 |
|
\resizebox{4in}{!}{ |
151 |
|
\includegraphics{part6/s12t_16x32.ps} |
152 |
|
} |
153 |
|
\end{center} |
154 |
|
\caption{Plot of a cubed sphere topology with a 32$\times$192 domain |
155 |
|
divided into six 32$\times$32 subdomains of two tiles each |
156 |
|
(\code{tnx=16, tny=32}). |
157 |
|
} \label{fig:12tile} |
158 |
|
\end{figure} |
159 |
|
|
160 |
|
\begin{figure} |
161 |
|
\begin{center} |
162 |
|
\resizebox{4in}{!}{ |
163 |
|
\includegraphics{part6/s6t_32x32.ps} |
164 |
|
} |
165 |
|
\end{center} |
166 |
|
\caption{Plot of a cubed sphere topology with a 32$\times$192 domain |
167 |
|
divided into six 32$\times$32 subdomains with one tile each |
168 |
|
(\code{tnx=32, tny=32}). This is the default configuration. |
169 |
|
} |
170 |
|
\label{fig:6tile} |
171 |
|
\end{figure} |
172 |
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|
173 |
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|
174 |
|
Tiles can be selected from the topology to be omitted from being |
175 |
|
allocated memory and processors. This tuning is useful in ocean |
176 |
|
modeling for omitting tiles that fall entirely on land. The tiles |
177 |
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omitted are specified in the file |
178 |
|
\filelink{blanklist.txt}{utils-exch2-matlab-topology-generator_blanklist.txt} |
179 |
|
by their tile number in the topology, separated by a newline. \\ |
180 |
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|
181 |
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|
182 |
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|
183 |
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|
184 |
|
\subsection{exch2, SIZE.h, and multiprocessing} |
185 |
|
\label{sec:exch2mpi} |
186 |
|
|
187 |
|
Once the topology configuration files are created, the Fortran |
188 |
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\code{PARAMETER}s in \file{SIZE.h} must be configured to match. |
189 |
|
Section \ref{sect:specifying_a_decomposition} \sectiontitle{Specifying |
190 |
|
a decomposition} provides a general description of domain |
191 |
|
decomposition within MITgcm and its relation to \file{SIZE.h}. The |
192 |
|
current section specifies certain constraints the exch2 package |
193 |
|
imposes as well as describes how to enable parallel execution with |
194 |
|
MPI. \\ |
195 |
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|
196 |
|
As in the general case, the parameters \varlink{sNx}{sNx} and |
197 |
|
\varlink{sNy}{sNy} define the size of the individual tiles, and so |
198 |
|
must be assigned the same respective values as \code{tnx} and |
199 |
|
\code{tny} in \file{driver.m}.\\ |
200 |
|
|
201 |
|
The halo width parameters \varlink{OLx}{OLx} and \varlink{OLy}{OLy} |
202 |
|
have no special bearing on exch2 and may be assigned as in the general |
203 |
|
case. The same holds for \varlink{Nr}{Nr}, the number of vertical |
204 |
|
levels in the model.\\ |
205 |
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|
206 |
|
The parameters \varlink{nSx}{nSx}, \varlink{nSy}{nSy}, |
207 |
|
\varlink{nPx}{nPx}, and \varlink{nPy}{nPy} relate to the number of |
208 |
|
tiles and how they are distributed on processors. When using exch2, |
209 |
|
the tiles are stored in single dimension, and so |
210 |
|
\code{\varlink{nSy}{nSy}=1} in all cases. Since the tiles as |
211 |
|
configured by exch2 cannot be split up accross processors without |
212 |
|
regenerating the topology, \code{\varlink{nPy}{nPy}=1} as well. \\ |
213 |
|
|
214 |
|
The number of tiles MITgcm allocates and how they are distributed |
215 |
|
between processors depends on \varlink{nPx}{nPx} and |
216 |
|
\varlink{nSx}{nSx}. \varlink{nSx}{nSx} is the number of tiles per |
217 |
|
processor and \varlink{nPx}{nPx} the number of processors. The total |
218 |
|
number of tiles in the topology minus those listed in |
219 |
|
\file{blanklist.txt} must equal \code{nSx*nPx}. \\ |
220 |
|
|
221 |
|
The following is an example of \file{SIZE.h} for the twelve-tile |
222 |
|
configuration illustrated in figure \ref{fig:12tile} running on |
223 |
|
one processor: \\ |
224 |
|
|
225 |
|
\begin{verbatim} |
226 |
|
PARAMETER ( |
227 |
|
& sNx = 16, |
228 |
|
& sNy = 32, |
229 |
|
& OLx = 2, |
230 |
|
& OLy = 2, |
231 |
|
& nSx = 12, |
232 |
|
& nSy = 1, |
233 |
|
& nPx = 1, |
234 |
|
& nPy = 1, |
235 |
|
& Nx = sNx*nSx*nPx, |
236 |
|
& Ny = sNy*nSy*nPy, |
237 |
|
& Nr = 5) |
238 |
|
\end{verbatim} |
239 |
|
|
240 |
|
The following is an example for the twentyfour-tile topology in figure |
241 |
|
\ref{fig:24tile} running on six processors: |
242 |
|
|
243 |
|
\begin{verbatim} |
244 |
|
PARAMETER ( |
245 |
|
& sNx = 16, |
246 |
|
& sNy = 16, |
247 |
|
& OLx = 2, |
248 |
|
& OLy = 2, |
249 |
|
& nSx = 4, |
250 |
|
& nSy = 1, |
251 |
|
& nPx = 6, |
252 |
|
& nPy = 1, |
253 |
|
& Nx = sNx*nSx*nPx, |
254 |
|
& Ny = sNy*nSy*nPy, |
255 |
|
& Nr = 5) |
256 |
|
\end{verbatim} |
257 |
|
|
258 |
|
|
259 |
|
|
260 |
|
|
261 |
|
|
262 |
\subsection{Key Variables} |
\subsection{Key Variables} |
263 |
|
|
264 |
The descriptions of the variables are divided up into scalars, |
The descriptions of the variables are divided up into scalars, |
265 |
one-dimensional arrays indexed to the tile number, and two and three |
one-dimensional arrays indexed to the tile number, and two and three |
266 |
dimensional |
dimensional arrays indexed to tile number and neighboring tile. This |
267 |
arrays indexed to tile number and neighboring tile. This division |
division reflects the functionality of these variables: The |
268 |
actually reflects the functionality of these variables: the scalars |
scalars are common to every part of the topology, the tile-indexed |
269 |
are common to every part of the topology, the tile-indexed arrays to |
arrays to individual tiles, and the arrays indexed by tile and |
270 |
individual tiles, and the arrays indexed to tile and neighbor to |
neighbor to relationships between tiles and their neighbors. \\ |
|
relationships between tiles and their neighbors. |
|
271 |
|
|
272 |
\subsubsection{Scalars} |
\subsubsection{Scalars} |
273 |
|
|
274 |
The number of tiles in a particular topology is set with the parameter |
The number of tiles in a particular topology is set with the parameter |
275 |
{\em NTILES}, and the maximum number of neighbors of any tiles by |
\code{NTILES}, and the maximum number of neighbors of any tiles by |
276 |
{\em MAX\_NEIGHBOURS}. These parameters are used for defining the size of |
\code{MAX\_NEIGHBOURS}. These parameters are used for defining the |
277 |
the various one and two dimensional arrays that store tile parameters |
size of the various one and two dimensional arrays that store tile |
278 |
indexed to the tile number. |
parameters indexed to the tile number and are assigned in the files |
279 |
|
generated by \file{driver.m}.\\ |
280 |
The scalar parameters {\em exch2\_domain\_nxt} and |
|
281 |
{\em exch2\_domain\_nyt} express the number of tiles in the x and y global |
The scalar parameters \varlink{exch2\_domain\_nxt}{exch2_domain_nxt} |
282 |
indices. For example, the default setup of six tiles has |
and \varlink{exch2\_domain\_nyt}{exch2_domain_nyt} express the number |
283 |
{\em exch2\_domain\_nxt=6} and {\em exch2\_domain\_nyt=1}. A topology of |
of tiles in the $x$ and $y$ global indices. For example, the default |
284 |
twenty-four square (in gridpoints) tiles, four (2x2) per subdomain, will |
setup of six tiles (Fig. \ref{fig:6tile}) has |
285 |
have {\em exch2\_domain\_nxt=12} and {\em exch2\_domain\_nyt=2}. Note |
\code{exch2\_domain\_nxt=6} and \code{exch2\_domain\_nyt=1}. A |
286 |
that these parameters express the tile layout to allow global data files that |
topology of twenty-four square tiles, four per subdomain (as in figure |
287 |
are tile-layout-neutral and have no bearing on the internal storage of the |
\ref{fig:24tile}), will have \code{exch2\_domain\_nxt=12} and |
288 |
arrays. The tiles are internally stored in a range from {\em 1,bi} (in the |
\code{exch2\_domain\_nyt=2}. Note that these parameters express the |
289 |
x axis) and y-axis variable {\em bj} is generally ignored within the package. |
tile layout to allow global data files that are tile-layout-neutral |
290 |
|
and have no bearing on the internal storage of the arrays. The tiles |
291 |
|
are internally stored in a range from \code{(1:\varlink{bi}{bi})} the |
292 |
|
$x$ axis, and the $y$ axis variable \varlink{bj}{bj} is generally |
293 |
|
ignored within the package. \\ |
294 |
|
|
295 |
\subsubsection{Arrays Indexed to Tile Number} |
\subsubsection{Arrays Indexed to Tile Number} |
296 |
|
|
297 |
The following arrays are of size {\em NTILES}, are indexed to the tile number, |
The following arrays are of length \code{NTILES}and are indexed to the |
298 |
and the indices are omitted in their descriptions. |
tile number, which is indicated in the diagrams with the notation |
299 |
|
\textsf{t}$n$. The indices are omitted in the descriptions. \\ |
300 |
|
|
301 |
|
The arrays \varlink{exch2\_tnx}{exch2_tnx} and |
302 |
|
\varlink{exch2\_tny}{exch2_tny} express the $x$ and $y$ dimensions of |
303 |
|
each tile. At present for each tile \texttt{exch2\_tnx=sNx} and |
304 |
|
\texttt{exch2\_tny=sNy}, as assigned in \file{SIZE.h} and described in |
305 |
|
section \ref{sec:exch2mpi} \sectiontitle{exch2, SIZE.h, and |
306 |
|
multiprocessing}. Future releases of MITgcm are to allow varying tile |
307 |
|
sizes. \\ |
308 |
|
|
309 |
|
The location of the tiles' Cartesian origin within a subdomain are |
310 |
|
determined by the arrays \varlink{exch2\_tbasex}{exch2_tbasex} and |
311 |
|
\varlink{exch2\_tbasey}{exch2_tbasey}. These variables are used to |
312 |
|
relate the location of the edges of different tiles to each other. As |
313 |
|
an example, in the default six-tile topology (Fig. \ref{fig:6tile}) |
314 |
|
each index in these arrays is set to \code{0} since a tile occupies |
315 |
|
its entire subdomain. The twentyfour-tile case discussed above will |
316 |
|
have values of \code{0} or \code{16}, depending on the quadrant the |
317 |
|
tile falls within the subdomain. The elements of the arrays |
318 |
|
\varlink{exch2\_txglobalo}{exch2_txglobalo} and |
319 |
|
\varlink{exch2\_txglobalo}{exch2_txglobalo} are similar to |
320 |
|
\varlink{exch2\_tbasex}{exch2_tbasex} and |
321 |
|
\varlink{exch2\_tbasey}{exch2_tbasey}, but locate the tiles within the |
322 |
|
global address space, similar to that used by global files. \\ |
323 |
|
|
324 |
|
The array \varlink{exch2\_myFace}{exch2_myFace} contains the number of |
325 |
|
the subdomain of each tile, in a range \code{(1:6)} in the case of the |
326 |
|
standard cube topology and indicated by \textbf{\textsf{f}}$n$ in |
327 |
|
figures \ref{fig:12tile} and |
328 |
|
\ref{fig:24tile}. \varlink{exch2\_nNeighbours}{exch2_nNeighbours} |
329 |
|
contains a count the neighboring tiles each tile has, and is |
330 |
|
used for setting bounds for looping over neighboring tiles. |
331 |
|
\varlink{exch2\_tProc}{exch2_tProc} holds the process rank of each |
332 |
|
tile, and is used in interprocess communication. \\ |
333 |
|
|
334 |
|
|
335 |
|
The arrays \varlink{exch2\_isWedge}{exch2_isWedge}, |
336 |
|
\varlink{exch2\_isEedge}{exch2_isEedge}, |
337 |
|
\varlink{exch2\_isSedge}{exch2_isSedge}, and |
338 |
|
\varlink{exch2\_isNedge}{exch2_isNedge} are set to \code{1} if the |
339 |
|
indexed tile lies on the respective edge of a subdomain, \code{0} if |
340 |
|
not. The values are used within the topology generator to determine |
341 |
|
the orientation of neighboring tiles, and to indicate whether a tile |
342 |
|
lies on the corner of a subdomain. The latter case requires special |
343 |
|
exchange and numerical handling for the singularities at the eight |
344 |
|
corners of the cube. \\ |
345 |
|
|
|
The arrays {\em exch2\_tnx} and {\em exch2\_tny} |
|
|
express the x and y dimensions of each tile. At present for each tile |
|
|
{\em exch2\_tnx = sNx} |
|
|
and {\em exch2\_tny = sNy}, as assigned in {\em SIZE.h}. Future releases of |
|
|
MITgcm are to allow varying tile sizes. |
|
|
|
|
|
The location of the tiles' Cartesian origin within a subdomain are determined |
|
|
by the arrays {\em exch2\_tbasex} and {\em exch2\_tbasey}. These variables |
|
|
are used to relate the location of the edges of the tiles to each other. As |
|
|
an example, in the default six-tile topology (the degenerate case) |
|
|
each index in these arrays are |
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|
set to 0. The twenty-four, 32x32 cube face case discussed above will have |
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values of 0 or 16, depending on the quadrant the tile falls within the |
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subdomain. {\em exch2\_myFace} contains the number of the |
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cubeface/subdomain of each tile, numbered 1-6 in the case of the standard |
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cube topology. |
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The arrays {\em exch2\_txglobalo} and {\em exch2\_txglobalo} are similar to |
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{\em exch2\_tbasex} and {\em exch2\_tbasey}, but locate the tiles within |
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the global address space, similar to that used by global files. |
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The arrays {\em exch2\_isWedge}, {\em exch2\_isEedge}, {\em exch2\_isSedge}, |
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and {\em exch2\_isNedge} are set to 1 if the indexed tile lies on the edge |
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of a subdomain, 0 if not. The values are used within the topology generator |
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to determine the orientation of neighboring tiles and to indicate whether |
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a tile lies on the corner of a subdomain. The latter case indicates |
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special exchange and numerical handling for the singularities at the eight |
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corners of the cube. {\em exch2\_isNedge} contains a count of how many |
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neighboring tiles each tile has, and is used for setting bounds for looping |
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over neighboring tiles. {\em exch2\_tProc} holds the process rank of each tile, |
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and is used in interprocess communication. |
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\subsubsection{Arrays Indexed to Tile Number and Neighbor} |
\subsubsection{Arrays Indexed to Tile Number and Neighbor} |
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The following arrays are all of size {\em MAX\_NEIGHBOURS}x{\em NTILES} and |
The following arrays are all of size |
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describe the orientations between the the tiles. |
\code{MAX\_NEIGHBOURS}$\times$\code{NTILES} and describe the |
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orientations between the the tiles. \\ |
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The array \code{exch2\_neighbourId(a,T)} holds the tile number |
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\code{Tn} for each of the tile number \code{T}'s neighboring tiles |
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\code{a}. The neighbor tiles are indexed |
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\code{(1:exch2\_NNeighbours(T))} in the order right to left on the |
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north then south edges, and then top to bottom on the east and west |
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edges. Maybe throw in a fig here, eh? \\ |
359 |
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\sloppy The \code{exch2\_opposingSend\_record(a,T)} array holds the |
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index \code{b} of the element in \texttt{exch2\_neighbourId(b,Tn)} |
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that holds the tile number \code{T}, given |
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\code{Tn=exch2\_neighborId(a,T)}. In other words, |
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\begin{verbatim} |
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exch2_neighbourId( exch2_opposingSend_record(a,T), |
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exch2_neighbourId(a,T) ) = T |
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\end{verbatim} |
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This provides a back-reference from the neighbor tiles. \\ |
369 |
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370 |
The array {\em exch2\_neighbourId(a,T)} holds the tile number $T_{n}$ for each tile |
The arrays \varlink{exch2\_pi}{exch2_pi} and |
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{\em T}'s neighbor tile {\em a}. The neighbor tiles are indexed {\em 1,MAX\_NEIGHBOURS } |
\varlink{exch2\_pj}{exch2_pj} specify the transformations of indices |
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in the order right to left on the north then south edges, and then top to bottom on the east |
in exchanges between the neighboring tiles. These transformations are |
373 |
and west edges. maybe throw in a fig here, eh? |
necessary in exchanges between subdomains because the array index in |
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one dimension may map to the other index in an adjacent subdomain, and |
375 |
{\em exch2\_opposingSend\_record(a,T)} holds |
may be have its indexing reversed. This swapping arises from the |
376 |
the index c in {\em exch2\_neighbourId(b,$T_{n}$)} that holds the tile number T. |
``folding'' of two-dimensional arrays into a three-dimensional cube. |
377 |
In other words, |
|
378 |
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The dimensions of \code{exch2\_pi(t,N,T)} and \code{exch2\_pj(t,N,T)} |
379 |
\begin{verbatim} |
are the neighbor ID \code{N} and the tile number \code{T} as explained |
380 |
exch2_neighbourId( exch2_opposingSend_record(a,T), |
above, plus a vector of length \code{2} containing transformation |
381 |
exch2_neighbourId(a,T) ) = T |
factors \code{t}. The first element of the transformation vector |
382 |
\end{verbatim} |
holds the factor to multiply the index in the same axis, and the |
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second element holds the the same for the orthogonal index. To |
384 |
% {\em exch2\_neighbourId(exch2\_opposingSend\_record(a,T),exch2\_neighbourId(a,T))=T}. |
clarify, \code{exch2\_pi(1,N,T)} holds the mapping of the $x$ axis |
385 |
% alternate version |
index of tile \code{T} to the $x$ axis of tile \code{T}'s neighbor |
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\code{N}, and \code{exch2\_pi(2,N,T)} holds the mapping of \code{T}'s |
387 |
This is to provide a backreference from the neighbor tiles. |
$x$ index to the neighbor \code{N}'s $y$ index. \\ |
388 |
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389 |
The arrays {\em exch2\_pi }, {\em exch2\_pj }, {\em exch2\_oi }, |
One of the two elements of \code{exch2\_pi} or \code{exch2\_pj} for a |
390 |
{\em exch2\_oj }, {\em exch2\_oi\_f }, and {\em exch2\_oj\_f } specify |
given tile \code{T} and neighbor \code{N} will be \code{0}, reflecting |
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the transformations in exchanges between the neighboring tiles. The dimensions |
the fact that the two axes are orthogonal. The other element will be |
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of {\em exch2\_pi(t,N,T) } and {\em exch2\_pj(t,N,T) } are the neighbor ID |
\code{1} or \code{-1}, depending on whether the axes are indexed in |
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{ \em N } and the tile number {\em T } as explained above, plus the transformation |
the same or opposite directions. For example, the transform vector of |
394 |
vector {\em t }, of length two. The first element of the transformation vector indicates |
the arrays for all tile neighbors on the same subdomain will be |
395 |
the factor by which variables representing the same vector component of a tile |
\code{(1,0)}, since all tiles on the same subdomain are oriented |
396 |
will be multiplied, and the second element indicates the transform to the |
identically. An axis that corresponds to the orthogonal dimension |
397 |
variable in the other direction. As an example, {\em exch2\_pi(1,N,T) } holds the |
with the same index direction in a particular tile-neighbor |
398 |
transform of the i-component of a vector variable in tile {\em T } to the i-component of |
orientation will have \code{(0,1)}. Those in the opposite index |
399 |
tile {\em T }'s neighbor {\em N }, and {\em exch2\_pi(2,N,T) } hold the component |
direction will have \code{(0,-1)} in order to reverse the ordering. \\ |
400 |
of neighbor {\em N }'s j-component. |
|
401 |
|
The arrays \varlink{exch2\_oi}{exch2_oi}, |
402 |
Under the current cube topology, one of the two elements of {\em exch2\_pi } or {\em exch2\_pj } |
\varlink{exch2\_oj}{exch2_oj}, \varlink{exch2\_oi\_f}{exch2_oi_f}, and |
403 |
for a given tile {\em T } and neighbor {\em N } will be 0, reflecting the fact that |
\varlink{exch2\_oj\_f}{exch2_oj_f} are indexed to tile number and |
404 |
the vector components are orthogonal. The other element will be 1 or -1, depending on whether |
neighbor and specify the relative offset within the subdomain of the |
405 |
the components are indexed in the same or opposite directions. For example, the transform dimension |
array index of a variable going from a neighboring tile $N$ to a local |
406 |
of the arrays for all tile neighbors on the same subdomain will be {\em [1 , 0] }, since all tiles on |
tile $T$. Consider the six-tile case (Fig. \ref{fig:6tile}), where |
407 |
the same subdomain are oriented identically. Vectors that correspond to the orthogonal dimension with the |
\code{exch2\_oi(1,1)=33}, \code{exch2\_oi(2,1)=0}, |
408 |
same index direction will have {\em [0 , 1] }, whereas those in the opposite index direction will have |
\code{exch2\_oi(3,1)=32}, and \code{exch2\_oi(4,1)=-32}. Each of these |
409 |
{\em [0 , -1] }. |
indicates the offset in the $x$ direction \\ |
410 |
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411 |
|
Finally, \varlink{exch2\_itlo\_c}{exch2_itlo_c}, |
412 |
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\varlink{exch2\_ithi\_c}{exch2_ithi_c}, |
413 |
|
\varlink{exch2\_jtlo\_c}{exch2_jtlo_c} and |
414 |
// |
\varlink{exch2\_jthi\_c}{exch2_jthi_c} hold the location and index |
415 |
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bounds of the edge segment of the neighbor tile \code{N}'s subdomain |
416 |
|
that gets exchanged with the local tile \code{T}. To take the example |
417 |
|
of tile \code{T=2} in the twelve-tile topology |
418 |
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(Fig. \ref{fig:12tile}): \\ |
419 |
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|
420 |
\begin{verbatim} |
\begin{verbatim} |
421 |
|
exch2_itlo_c(4,2)=17 |
422 |
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exch2_ithi_c(4,2)=17 |
423 |
|
exch2_jtlo_c(4,2)=0 |
424 |
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exch2_jthi_c(4,2)=33 |
425 |
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\end{verbatim} |
426 |
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427 |
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Here \code{N=4}, indicating the western neighbor, which is \code{Tn=1}. |
428 |
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\code{Tn=1} resides on the same subdomain as \code{T=2}, so the tiles |
429 |
|
have the same orientation and the same $x$ and $y$ axes. The $i$ |
430 |
|
component is orthogonal to the western edge and the tile is 16 points |
431 |
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wide, so \code{exch2\_itlo\_c} and \code{exch2\_ithi\_c} indicate the |
432 |
|
column beyond \code{Tn=1}'s eastern edge, in that tile's halo |
433 |
|
region. Since the border of the tiles extends through the entire |
434 |
|
height of the subdomain, the $y$ axis bounds \code{exch2\_jtlo\_c} to |
435 |
|
\code{exch2\_jthi\_c} cover the height, plus 1 in either direction to |
436 |
|
cover part of the halo. \\ |
437 |
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|
438 |
|
For the north edge of the same tile \code{T=2} where \code{N=1} and |
439 |
|
the neighbor tile is \code{Tn=5}: |
440 |
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|
441 |
|
\begin{verbatim} |
442 |
C exch2_pi :: X index row of target to source permutation |
exch2_itlo_c(1,2)=0 |
443 |
C :: matrix for each neighbour entry. |
exch2_ithi_c(1,2)=0 |
444 |
C exch2_pj :: Y index row of target to source permutation |
exch2_jtlo_c(1,2)=0 |
445 |
C :: matrix for each neighbour entry. |
exch2_jthi_c(1,2)=17 |
|
C exch2_oi :: X index element of target to source |
|
|
C :: offset vector for cell-centered quantities |
|
|
C :: of each neighbor entry. |
|
|
C exch2_oj :: Y index element of target to source |
|
|
C :: offset vector for cell-centered quantities |
|
|
C :: of each neighbor entry. |
|
|
C exch2_oi_f :: X index element of target to source |
|
|
C :: offset vector for face quantities |
|
|
C :: of each neighbor entry. |
|
|
C exch2_oj_f :: Y index element of target to source |
|
|
C :: offset vector for face quantities |
|
|
C :: of each neighbor entry. |
|
446 |
\end{verbatim} |
\end{verbatim} |
447 |
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448 |
|
\code{T}'s northern edge is parallel to the $x$ axis, but since |
449 |
|
\code{Tn}'s $y$ axis corresponds to \code{T}'s $x$ axis, |
450 |
|
\code{T}'s northern edge exchanges with \code{Tn}'s western edge. |
451 |
|
The western edge of the tiles corresponds to the lower bound of the |
452 |
|
$x$ axis, so \code{exch2\_itlo\_c} \code{exch2\_ithi\_c} are \code{0}. The |
453 |
|
range of \code{exch2\_jtlo\_c} and \code{exch2\_jthi\_c} correspond to the |
454 |
|
width of \code{T}'s northern edge, plus the halo. \\ |
455 |
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456 |
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457 |
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458 |
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459 |
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460 |
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461 |
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462 |
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463 |
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464 |
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465 |
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466 |
|
This needs some diagrams. \\ |
467 |
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468 |
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469 |
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