Difference between revisions of "MPI Hello World"

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(Created page with "== MPI Hello World == Many parallel jobs are using MPI at the lowest level to manage parallel compute resources. This is a 'Hello World' program that will test the operation...")
 
 
(12 intermediate revisions by one other user not shown)
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== MPI Hello World ==
  
== MPI Hello World ==
   
−
Many parallel jobs are using MPI at the lowest level to manage parallel compute resources.
 +
Many parallel jobs are using [https://en.wikipedia.org/wiki/Message_Passing_Interface MPI] at the lowest level to manage parallel compute resources. You will want to successfully run this example to make sure your parallel computing environment is working properly. These instructions assume you've already set up your cluster ssh keys, as described in [[Cluster SSH access]]
   
 
This is a 'Hello World' program that will test the operation of sending jobs to remote workers.
  
This is a 'Hello World' program that will test the operation of sending jobs to remote workers.
  +
<nowiki>
−  
−
<code>
  
 
/*
  
/*
 
* Sample MPI "hello world" application in C
  
* Sample MPI "hello world" application in C
Line 16: Line 15:
 
int main(int argc, char* argv[])
  
int main(int argc, char* argv[])
 
{
  
{
−
int rank, size, len;
 +
int rank, size;
−
char version[MPI_MAX_LIBRARY_VERSION_STRING];
  
   
 
MPI_Init(&argc, &argv);
  
MPI_Init(&argc, &argv);
 
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
 
MPI_Comm_size(MPI_COMM_WORLD, &size);
  
MPI_Comm_size(MPI_COMM_WORLD, &size);
  +
printf("Hello, world, I am %d of %d \n", rank, size);
−
MPI_Get_library_version(version, &len);
  
−
printf("Hello, world, I am %d of %d, (%s, %d)\n",
  
−
rank, size, version, len);
  
 
MPI_Finalize();
  
MPI_Finalize();
   
 
return 0;
  
return 0;
 
}
  
}
  +
</nowiki>
  +
  +
create a folder and save this file as <tt> hello_mpi.c </tt>
  +
  +
You can compile this program with
  +
  +
mpicc -g hello_mpi.c -o hello_mpi
  +
  +
You now have an executable called <tt> hello_mpi </tt>
  +
  +
You can run the command with
  +
  +
mpirun ./hello_mpi
  +
  +
With no other arguments, mpirun will run all of the tasks on the local machine, usually one for each CPU core. You should see a hello world from each process, on each cpu core.
  +
  +
Now, to run your mpi program on the cluster, you will need to create a hostfile.
  +
First, lets create a simple hostfile that just runs four processes on the local machine
  +
  +
  +
Put the following line in a file called <tt>localhost </tt>.
  +
  +
<nowiki>
  +
localhost slots=4 max_slots=8
  +
</nowiki>
  +
  +
Now run your program with that hostfile, using
  +
  +
mpirun --hostfile localhost ./hello_mpi
  +
  +
<nowiki>
  +
Hello, world, I am 0 of 4
  +
Hello, world, I am 2 of 4
  +
Hello, world, I am 1 of 4
  +
Hello, world, I am 3 of 4
  +
</nowiki>
  +
  +
Now create a hostfile called <tt> cluster_hosts </tt> with the following entries:
  +
<nowiki>
  +
pnode01 slots=4 max_slots=8
  +
pnode02 slots=4 max_slots=8
  +
pnode03 slots=4 max_slots=8
  +
pnode04 slots=4 max_slots=8
  +
</nowiki>
  +
  +
and keep adding lines until you get to <tt> pnode64 slots=4 max_slots=8 </tt>.
  +
  +
The next step assumes you have set up your ssh keys as described in [[Cluster SSH access]]
  +
  +
With 64 nodes listed in your <tt> cluster_hosts </tt> file, run your program again with
  +
  +
mpirun --hostfile cluster_hosts ./hello_mpi
  +
  +
You should see the output shown below, which is 256 lines long, four responses from each host, one for each core described.
  +
  +
Once you are able to run this program successfully, your MPI setup is working. This will be necessary before you can run other MPI-based programs, such as ipyparallel programs which use MPI.
  +
  +
Note: the example below was run on 40 nodes.
   
−
</code>
 +
<nowiki>
  +
Hello, world, I am 126 of 160
  +
Hello, world, I am 69 of 160
  +
Hello, world, I am 159 of 160
  +
Hello, world, I am 137 of 160
  +
Hello, world, I am 11 of 160
  +
Hello, world, I am 138 of 160
  +
Hello, world, I am 139 of 160
  +
Hello, world, I am 3 of 160
  +
Hello, world, I am 125 of 160
  +
Hello, world, I am 68 of 160
  +
Hello, world, I am 0 of 160
  +
Hello, world, I am 127 of 160
  +
Hello, world, I am 71 of 160
  +
Hello, world, I am 8 of 160
  +
Hello, world, I am 136 of 160
  +
Hello, world, I am 85 of 160
  +
Hello, world, I am 2 of 160
  +
Hello, world, I am 124 of 160
  +
Hello, world, I am 70 of 160
  +
Hello, world, I am 51 of 160
  +
Hello, world, I am 9 of 160
  +
Hello, world, I am 86 of 160
  +
Hello, world, I am 21 of 160
  +
Hello, world, I am 1 of 160
  +
Hello, world, I am 25 of 160
  +
Hello, world, I am 143 of 160
  +
Hello, world, I am 119 of 160
  +
Hello, world, I am 6 of 160
  +
Hello, world, I am 10 of 160
  +
Hello, world, I am 84 of 160
  +
Hello, world, I am 133 of 160
  +
Hello, world, I am 156 of 160
  +
Hello, world, I am 23 of 160
  +
Hello, world, I am 100 of 160
  +
Hello, world, I am 146 of 160
  +
Hello, world, I am 27 of 160
  +
Hello, world, I am 118 of 160
  +
Hello, world, I am 55 of 160
  +
Hello, world, I am 32 of 160
  +
Hello, world, I am 123 of 160
  +
Hello, world, I am 67 of 160
  +
Hello, world, I am 87 of 160
  +
Hello, world, I am 135 of 160
  +
Hello, world, I am 157 of 160
  +
Hello, world, I am 20 of 160
  +
Hello, world, I am 130 of 160
  +
Hello, world, I am 120 of 160
  +
Hello, world, I am 12 of 160
  +
Hello, world, I am 82 of 160
  +
Hello, world, I am 48 of 160
  +
Hello, world, I am 132 of 160
  +
Hello, world, I am 158 of 160
  +
Hello, world, I am 22 of 160
  +
Hello, world, I am 131 of 160
  +
Hello, world, I am 101 of 160
  +
Hello, world, I am 145 of 160
  +
Hello, world, I am 24 of 160
  +
Hello, world, I am 140 of 160
  +
Hello, world, I am 117 of 160
  +
Hello, world, I am 113 of 160
  +
Hello, world, I am 154 of 160
  +
Hello, world, I am 7 of 160
  +
Hello, world, I am 53 of 160
  +
Hello, world, I am 33 of 160
  +
Hello, world, I am 16 of 160
  +
Hello, world, I am 28 of 160
  +
Hello, world, I am 111 of 160
  +
Hello, world, I am 121 of 160
  +
Hello, world, I am 13 of 160
  +
Hello, world, I am 64 of 160
  +
Hello, world, I am 88 of 160
  +
Hello, world, I am 96 of 160
  +
Hello, world, I am 83 of 160
  +
Hello, world, I am 49 of 160
  +
Hello, world, I am 134 of 160
  +
Hello, world, I am 128 of 160
  +
Hello, world, I am 102 of 160
  +
Hello, world, I am 148 of 160
  +
Hello, world, I am 147 of 160
  +
Hello, world, I am 26 of 160
  +
Hello, world, I am 36 of 160
  +
Hello, world, I am 141 of 160
  +
Hello, world, I am 58 of 160
  +
Hello, world, I am 73 of 160
  +
Hello, world, I am 46 of 160
  +
Hello, world, I am 116 of 160
  +
Hello, world, I am 114 of 160
  +
Hello, world, I am 155 of 160
  +
Hello, world, I am 4 of 160
  +
Hello, world, I am 52 of 160
  +
Hello, world, I am 34 of 160
  +
Hello, world, I am 62 of 160
  +
Hello, world, I am 17 of 160
  +
Hello, world, I am 29 of 160
  +
Hello, world, I am 76 of 160
  +
Hello, world, I am 92 of 160
  +
Hello, world, I am 81 of 160
  +
Hello, world, I am 50 of 160
  +
Hello, world, I am 129 of 160
  +
Hello, world, I am 103 of 160
  +
Hello, world, I am 149 of 160
  +
Hello, world, I am 144 of 160
  +
Hello, world, I am 37 of 160
  +
Hello, world, I am 142 of 160
  +
Hello, world, I am 56 of 160
  +
Hello, world, I am 75 of 160
  +
Hello, world, I am 47 of 160
  +
Hello, world, I am 40 of 160
  +
Hello, world, I am 106 of 160
  +
Hello, world, I am 115 of 160
  +
Hello, world, I am 152 of 160
  +
Hello, world, I am 5 of 160
  +
Hello, world, I am 54 of 160
  +
Hello, world, I am 35 of 160
  +
Hello, world, I am 63 of 160
  +
Hello, world, I am 18 of 160
  +
Hello, world, I am 30 of 160
  +
Hello, world, I am 77 of 160
  +
Hello, world, I am 93 of 160
  +
Hello, world, I am 108 of 160
  +
Hello, world, I am 122 of 160
  +
Hello, world, I am 14 of 160
  +
Hello, world, I am 65 of 160
  +
Hello, world, I am 89 of 160
  +
Hello, world, I am 99 of 160
  +
Hello, world, I am 153 of 160
  +
Hello, world, I am 61 of 160
  +
Hello, world, I am 19 of 160
  +
Hello, world, I am 31 of 160
  +
Hello, world, I am 78 of 160
  +
Hello, world, I am 94 of 160
  +
Hello, world, I am 109 of 160
  +
Hello, world, I am 15 of 160
  +
Hello, world, I am 66 of 160
  +
Hello, world, I am 91 of 160
  +
Hello, world, I am 97 of 160
  +
Hello, world, I am 80 of 160
  +
Hello, world, I am 150 of 160
  +
Hello, world, I am 38 of 160
  +
Hello, world, I am 57 of 160
  +
Hello, world, I am 72 of 160
  +
Hello, world, I am 44 of 160
  +
Hello, world, I am 41 of 160
  +
Hello, world, I am 107 of 160
  +
Hello, world, I am 112 of 160
  +
Hello, world, I am 59 of 160
  +
Hello, world, I am 74 of 160
  +
Hello, world, I am 45 of 160
  +
Hello, world, I am 42 of 160
  +
Hello, world, I am 104 of 160
  +
Hello, world, I am 79 of 160
  +
Hello, world, I am 110 of 160
  +
Hello, world, I am 90 of 160
  +
Hello, world, I am 98 of 160
  +
Hello, world, I am 151 of 160
  +
Hello, world, I am 39 of 160
  +
Hello, world, I am 43 of 160
  +
Hello, world, I am 105 of 160
  +
Hello, world, I am 60 of 160
  +
Hello, world, I am 95 of 160
  +
</nowiki>

Latest revision as of 01:07, 21 December 2022

MPI Hello World

Many parallel jobs are using MPI at the lowest level to manage parallel compute resources. You will want to successfully run this example to make sure your parallel computing environment is working properly. These instructions assume you've already set up your cluster ssh keys, as described in Cluster SSH access

This is a 'Hello World' program that will test the operation of sending jobs to remote workers. 

 /*
 * Sample MPI "hello world" application in C
 */


#include <stdio.h>
#include "mpi.h"

int main(int argc, char* argv[])
{
    int rank, size;

    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    MPI_Comm_size(MPI_COMM_WORLD, &size);
    printf("Hello, world, I am %d of %d \n", rank, size);
    MPI_Finalize();

    return 0;
}

create a folder and save this file as hello_mpi.c

You can compile this program with 

mpicc -g hello_mpi.c -o hello_mpi

You now have an executable called hello_mpi

You can run the command with 

mpirun ./hello_mpi

With no other arguments, mpirun will run all of the tasks on the local machine, usually one for each CPU core. You should see a hello world from each process, on each cpu core.

Now, to run your mpi program on the cluster, you will need to create a hostfile. First, lets create a simple hostfile that just runs four processes on the local machine


Put the following line in a file called localhost . 

localhost slots=4 max_slots=8

Now run your program with that hostfile, using 

mpirun --hostfile localhost ./hello_mpi

Hello, world, I am 0 of 4 
Hello, world, I am 2 of 4 
Hello, world, I am 1 of 4 
Hello, world, I am 3 of 4

Now create a hostfile called cluster_hosts with the following entries: 

pnode01 slots=4 max_slots=8
pnode02 slots=4 max_slots=8
pnode03 slots=4 max_slots=8
pnode04 slots=4 max_slots=8

and keep adding lines until you get to pnode64 slots=4 max_slots=8 .

The next step assumes you have set up your ssh keys as described in Cluster SSH access

With 64 nodes listed in your cluster_hosts file, run your program again with 

mpirun --hostfile cluster_hosts ./hello_mpi

You should see the output shown below, which is 256 lines long, four responses from each host, one for each core described.

Once you are able to run this program successfully, your MPI setup is working. This will be necessary before you can run other MPI-based programs, such as ipyparallel programs which use MPI.

Note: the example below was run on 40 nodes. 

Hello, world, I am 126 of 160 
Hello, world, I am 69 of 160 
Hello, world, I am 159 of 160 
Hello, world, I am 137 of 160 
Hello, world, I am 11 of 160 
Hello, world, I am 138 of 160 
Hello, world, I am 139 of 160 
Hello, world, I am 3 of 160 
Hello, world, I am 125 of 160 
Hello, world, I am 68 of 160 
Hello, world, I am 0 of 160 
Hello, world, I am 127 of 160 
Hello, world, I am 71 of 160 
Hello, world, I am 8 of 160 
Hello, world, I am 136 of 160 
Hello, world, I am 85 of 160 
Hello, world, I am 2 of 160 
Hello, world, I am 124 of 160 
Hello, world, I am 70 of 160 
Hello, world, I am 51 of 160 
Hello, world, I am 9 of 160 
Hello, world, I am 86 of 160 
Hello, world, I am 21 of 160 
Hello, world, I am 1 of 160 
Hello, world, I am 25 of 160 
Hello, world, I am 143 of 160 
Hello, world, I am 119 of 160 
Hello, world, I am 6 of 160 
Hello, world, I am 10 of 160 
Hello, world, I am 84 of 160 
Hello, world, I am 133 of 160 
Hello, world, I am 156 of 160 
Hello, world, I am 23 of 160 
Hello, world, I am 100 of 160 
Hello, world, I am 146 of 160 
Hello, world, I am 27 of 160 
Hello, world, I am 118 of 160 
Hello, world, I am 55 of 160 
Hello, world, I am 32 of 160 
Hello, world, I am 123 of 160 
Hello, world, I am 67 of 160 
Hello, world, I am 87 of 160 
Hello, world, I am 135 of 160 
Hello, world, I am 157 of 160 
Hello, world, I am 20 of 160 
Hello, world, I am 130 of 160 
Hello, world, I am 120 of 160 
Hello, world, I am 12 of 160 
Hello, world, I am 82 of 160 
Hello, world, I am 48 of 160 
Hello, world, I am 132 of 160 
Hello, world, I am 158 of 160 
Hello, world, I am 22 of 160 
Hello, world, I am 131 of 160 
Hello, world, I am 101 of 160 
Hello, world, I am 145 of 160 
Hello, world, I am 24 of 160 
Hello, world, I am 140 of 160 
Hello, world, I am 117 of 160 
Hello, world, I am 113 of 160 
Hello, world, I am 154 of 160 
Hello, world, I am 7 of 160 
Hello, world, I am 53 of 160 
Hello, world, I am 33 of 160 
Hello, world, I am 16 of 160 
Hello, world, I am 28 of 160 
Hello, world, I am 111 of 160 
Hello, world, I am 121 of 160 
Hello, world, I am 13 of 160 
Hello, world, I am 64 of 160 
Hello, world, I am 88 of 160 
Hello, world, I am 96 of 160 
Hello, world, I am 83 of 160 
Hello, world, I am 49 of 160 
Hello, world, I am 134 of 160 
Hello, world, I am 128 of 160 
Hello, world, I am 102 of 160 
Hello, world, I am 148 of 160 
Hello, world, I am 147 of 160 
Hello, world, I am 26 of 160 
Hello, world, I am 36 of 160 
Hello, world, I am 141 of 160 
Hello, world, I am 58 of 160 
Hello, world, I am 73 of 160 
Hello, world, I am 46 of 160 
Hello, world, I am 116 of 160 
Hello, world, I am 114 of 160 
Hello, world, I am 155 of 160 
Hello, world, I am 4 of 160 
Hello, world, I am 52 of 160 
Hello, world, I am 34 of 160 
Hello, world, I am 62 of 160 
Hello, world, I am 17 of 160 
Hello, world, I am 29 of 160 
Hello, world, I am 76 of 160 
Hello, world, I am 92 of 160 
Hello, world, I am 81 of 160 
Hello, world, I am 50 of 160 
Hello, world, I am 129 of 160 
Hello, world, I am 103 of 160 
Hello, world, I am 149 of 160 
Hello, world, I am 144 of 160 
Hello, world, I am 37 of 160 
Hello, world, I am 142 of 160 
Hello, world, I am 56 of 160 
Hello, world, I am 75 of 160 
Hello, world, I am 47 of 160 
Hello, world, I am 40 of 160 
Hello, world, I am 106 of 160 
Hello, world, I am 115 of 160 
Hello, world, I am 152 of 160 
Hello, world, I am 5 of 160 
Hello, world, I am 54 of 160 
Hello, world, I am 35 of 160 
Hello, world, I am 63 of 160 
Hello, world, I am 18 of 160 
Hello, world, I am 30 of 160 
Hello, world, I am 77 of 160 
Hello, world, I am 93 of 160 
Hello, world, I am 108 of 160 
Hello, world, I am 122 of 160 
Hello, world, I am 14 of 160 
Hello, world, I am 65 of 160 
Hello, world, I am 89 of 160 
Hello, world, I am 99 of 160 
Hello, world, I am 153 of 160 
Hello, world, I am 61 of 160 
Hello, world, I am 19 of 160 
Hello, world, I am 31 of 160 
Hello, world, I am 78 of 160 
Hello, world, I am 94 of 160 
Hello, world, I am 109 of 160 
Hello, world, I am 15 of 160 
Hello, world, I am 66 of 160 
Hello, world, I am 91 of 160 
Hello, world, I am 97 of 160 
Hello, world, I am 80 of 160 
Hello, world, I am 150 of 160 
Hello, world, I am 38 of 160 
Hello, world, I am 57 of 160 
Hello, world, I am 72 of 160 
Hello, world, I am 44 of 160 
Hello, world, I am 41 of 160 
Hello, world, I am 107 of 160 
Hello, world, I am 112 of 160 
Hello, world, I am 59 of 160 
Hello, world, I am 74 of 160 
Hello, world, I am 45 of 160 
Hello, world, I am 42 of 160 
Hello, world, I am 104 of 160 
Hello, world, I am 79 of 160 
Hello, world, I am 110 of 160 
Hello, world, I am 90 of 160 
Hello, world, I am 98 of 160 
Hello, world, I am 151 of 160 
Hello, world, I am 39 of 160 
Hello, world, I am 43 of 160 
Hello, world, I am 105 of 160 
Hello, world, I am 60 of 160 
Hello, world, I am 95 of 160
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