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Mon Apr 6 06:41:49 2009 UTC (11 years, 9 months ago) by gross
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some modifications to docu for MPI
1 gross 2316 \chapter{Execution of an {\it escript} Script}
2     \label{EXECUTION}
4     \section{Overview}
5 jfenwick 2331 A typical way of starting your {\it escript} script \file{myscript.py} is with the \program{escript} command\footnote{The \program{escript} launcher is not supported under \WINDOWS yet.}:
6 gross 2316 \begin{verbatim}
7     escript myscript.py
8     \end{verbatim}
9 jfenwick 2331 as already shown in section~\ref{FirstSteps}\footnote{For this discussion, it is assumed that \program{escript} is included in your \env{PATH} environment. See installation guide for details.}
10     . In some cases
11     it can be useful to work interactively e.g. when debugging a script, with the command
12 gross 2316 \begin{verbatim}
13     escript -i myscript.py
14     \end{verbatim}
15 jfenwick 2331 This will execute \var{myscript.py} and when it completes (or an error occurs), a \PYTHON prompt will be provided.
16     To leave the prompt press \kbd{Control-d}.
17 gross 2316
18     To start
19     \program{escript} using four threads (eg. if you use a multi-core processor) you can use
20     \begin{verbatim}
21     escript -t 4 myscript.py
22     \end{verbatim}
23 jfenwick 2331 This will require {\it escript} to be compiled for \OPENMP\cite{OPENMP}.
24 gross 2316
25 jfenwick 2331 To start \program{escript} using \MPI\cite{MPI} with $8$ processes you use
26 gross 2316 \begin{verbatim}
27 jfenwick 2331 escript -p 8 myscript.py
28 gross 2316 \end{verbatim}
29 jfenwick 2331 If the processors which are used are multi--core processors or multi--processor shared memory archtiectures you can use threading in addition to \MPI. For instance to run $8$ \MPI processes with using $4$ threads each, you use the command
30 gross 2316 \begin{verbatim}
31 jfenwick 2331 escript -p 8 -t 4 myscript.py
32 gross 2316 \end{verbatim}
33 jfenwick 2331 In the case of a super computer or a cluster, you may wish to distribute the workload over a number of nodes\footnote{For simplicity, we will use the term node to refer to either a node in a super computer or an individual machine in a cluster}.
34     For example, to use $8$ nodes, with $4$ \MPI processes per node, write
35 gross 2316 \begin{verbatim}
36 jfenwick 2331 escript -n 8 -p 4 myscript.py
37 gross 2316 \end{verbatim}
38 jfenwick 2331 Since threading has some performance advantages over processes, you may specify a number of threads as well.
39     \begin{verbatim}
40     escript -n 8 -p 4 -t 2 myscript.py
41     \end{verbatim}
42     This runs the script on $8$ nodes, with $4$ processes per node and $2$ threads per process.
43 gross 2316
44     \section{Options}
45     The general form of the \program{escript} launcher is as follows:
47 jfenwick 2345 %%%%
48     % If you are thinking about changing this please remember to update the man page as well
49     %%%%
51 gross 2316 \program{escript}
52     \optional{\programopt{-n \var{nn}}}
53 jfenwick 2331 \optional{\programopt{-p \var{np}}}
54 gross 2316 \optional{\programopt{-t \var{nt}}}
55     \optional{\programopt{-f \var{hostfile}}}
56     \optional{\programopt{-x}}
57     \optional{\programopt{-V}}
58     \optional{\programopt{-e}}
59     \optional{\programopt{-h}}
60     \optional{\programopt{-v}}
61     \optional{\programopt{-o}}
62     \optional{\programopt{-c}}
63     \optional{\programopt{-i}}
64 jfenwick 2343 \optional{\programopt{-b}}
65 gross 2316 \optional{\var{file}}
66     \optional{\var{ARGS}}
68 jfenwick 2331 where \var{file} is the name of a script, \var{ARGS} are arguments for the script.
69     The \program{escript} program will import your current environment variables.
70     If no \var{file} is given, then you will be given a \PYTHON prompt (see \programopt{-i} for restrictions).
72 gross 2316 The options are used as follows:
73     \begin{itemize}
75     \item[\programopt{-n} \var{nn}] the number of compute nodes \var{nn} to be used. The total number of process being used is
76 gross 2363 $\var{nn} \cdot \var{ns}$. This option overwrites the value of the \env{ESCRIPT_NUM_NODES} environment variable.
77     If a hostfile is given, the number of nodes needs to match the number hosts given in the host file.
78     If $\var{nn}>1$ but {\it escript} is not compiled for \MPI a warning is printed but execution is continued with $\var{nn}=1$. If \programopt{-n} is not set the
79 gross 2350 number of hosts in the host file is used. The default value is 1.
80 gross 2316
81 jfenwick 2345 \item[\programopt{-p} \var{np}] the number of MPI processes per node. The total number of processes to be used is
82 gross 2370 $\var{nn} \cdot \var{np}$. This option overwrites the value of the \env{ESCRIPT_NUM_PROCS} environment variable. If $\var{np}>1$ but {\it escript} is not compiled for \MPI a warning is printed but execution is continued with $\var{np}=1$. The default value is 1.
83 gross 2316
84 jfenwick 2331 \item[\programopt{-t} \var{nt}] the number of threads used per processes.
85     The option overwrites the value of the \env{ESCRIPT_NUM_THREADS} environment variable.
86     If $\var{nt}>1$ but {\it escript} is not compiled for \OPENMP a warning is printed but execution is continued with $\var{nt}=1$. The default value is 1.
87 gross 2316
88 gross 2350 \item[\programopt{-f} \var{hostfile}] the name of a file with a list of host names. Some systems require to specify the addresses or names of the compute nodes where \MPI process should be spawned. The list of addresses or names of the compute nodes is listed in the file with the name \var{hostfile}. If \programopt{-n} is set the
89     the number of different
90     hosts defined in \var{hostfile} must be equal to the number of requsted compute nodes \var{nn}. The option overwrites the value of the \env{ESCRIPT_HOSTFILE} environment variable. By default value no host file is used.
91 gross 2316 \item[\programopt{-c}] prints the information about the settings used to compile {\it escript} and stops execution..
92     \item[\programopt{-V}] prints the version of {\it escript} and stops execution.
93     \item[\programopt{-h}] prints a help message and stops execution.
94 jfenwick 2343 \item[\programopt{-i}] executes the script \var{file} and switches to interactive mode after the execution is finished or an exception has occured. This option is useful for debugging a script. The option cannot be used if more then one process ($\var{nn} \cdot \var{np}>1$) is used.
95     \item[\programopt{-b}] do not invoke python. This is used to run non-python programs.
96 gross 2316
97 jfenwick 2331 \item[\programopt{-e}] shows additional environment variables and commands used during \program{escript} execution. This option is useful if users wish to excute scripts without using the \program{escript} command.
98 gross 2316
99 gross 2355 \item[\programopt{-o}] switches on the redirection of output of processors with \MPI rank greater than zero to the files \file{stdout_\var{r}.out} and \file{stderr_\var{r}.out} where \var{r} is the rank of the processor. The option overwrites the value of the \env{ESCRIPT_STDFILES} environment variable
100 gross 2316
101 jfenwick 2331 % \item[\programopt{-x}] interpret \var{file} as an \esysxml \footnote{{\it esysxml} has not been released yet.} task.
102     % This option is still expermental.
103 gross 2316
104     \item[\programopt{-v}] prints some diagonstic information.
105     \end{itemize}
106 gross 2370 \subsection{Notes}
107     \begin{itemize}
108     \item Make sure that \program{mpiexec} is in your \env{PATH}.
109     \item For MPICH and INTELMPI and for the case a hostfile is present
110     \program{escript} will start the \program{mpd} demon before execution.
111     \end{itemize}
112 gross 2316
113     \section{Input and Output}
114 jfenwick 2331 When \MPI is used on more than one process ($\var{nn} \cdot \var{np} >1$) no input from the standard input is accepted. Standard output on any process other the the master process (\var{rank}=0) will not be available.
115     Error output from any processor will be redirected to the node where \program{escript} has been envoked.
116 gross 2355 If the \programopt{-o} or \env{ESCRIPT_STDFILES} is set\footnote{That is, it has a non-empty value.}, then the standard and error output from any process other than the master process will be written to files of the names \file{stdout_\var{r}.out} and \file{stderr_\var{r}.out} (where
117 jfenwick 2331 \var{r} is the rank of the process).
118 gross 2316
119 jfenwick 2331 If files are created or read by individual \MPI processes with information local to the process (e.g in the \function{dump} function) and more than one process is used ($\var{nn} \cdot \var{np} >1$), the \MPI process rank is appended to the file names.
120     This will avoid problems if processes are using a shared file system.
121     Files which collect data which are global for all \MPI processors will created by the process with \MPI rank 0 only.
122     Users should keep in mind that if the file system is not shared, then a file containing global information
123 gross 2316 which is read by all processors needs to be copied to the local file system before \program{escript} is invoked.
126     \section{Hints for MPI programming}
127     Later

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