Running MPI on 2 laptops

ahsan_smme.nust@yahoo.com · December 12, 2013, 15:02

I am trying to run airfoil 2D case on two laptops . I made my own blockMesh having 1.1 million cells. I have 2 laptops both having 4 processors. Same openfoam version 2.2.1 and ubuntu 12.04LTS version. I gave decomposePar in both laptops for the same case airfoil2D
The problem is when i give command
mpirun --hostfile hosts -np 8 simpleFoam -parallel
in terminal, where hosts file contain names and number of processors of slave.Its located inside airfoil2D folder.
Host file:
ahsan@ahsan-Inspiron-5521
Dell-4050 cpu=4

I get this error:

ahsan@ahsan-Inspiron-5521:~/airFoil2D$ mpirun --hostfile hosts -np 8 simpleFoam -parallel
ssh: Could not resolve hostname Dell-4050: Name or service not known
--------------------------------------------------------------------------
A daemon (pid 12100) died unexpectedly with status 255 while attempting
to launch so we are aborting.

There may be more information reported by the environment (see above).

This may be because the daemon was unable to find all the needed shared
libraries on the remote node. You may set your LD_LIBRARY_PATH to have the
location of the shared libraries on the remote nodes and this will
automatically be forwarded to the remote nodes.
--------------------------------------------------------------------------
--------------------------------------------------------------------------
mpirun noticed that the job aborted, but has no info as to the process
that caused that situation.
--------------------------------------------------------------------------
mpirun: clean termination accomplished

Dell 4050 is my slave. I read posts about running MPI on clusters but couldn’t understand how to give library path as i'm not much of a programmer and new to ubuntu. This is my final year project if any1 can help me out ill be more than thankful.

wyldckat · December 15, 2013, 15:18

Greetings Ahsan,

Two reference posts that can come in handy:

So, basically what happens in your case is two things:

The two laptops are not aware of the host names of each other, therefore are not able to find their corresponding IP address.
Your "machines" file is incorrect.

To solve the problem, you must first find the IP address for each laptop. You can use this command:

Code:

ifconfig

And then look for the IP address at "inet addr:" related to "eth0", "eth1" or "wlan0" or "wlan1".
Make a note of those IP addresses and try pinging the other machine, using it's IP address, to check if it can find it. For example:

If "machine1" has the IP "11.12.13.14";
and if "machine2" has the IP "11.12.13.132";

Then:

From "machine2", run:
Code:
```
ping 11.12.13.14
```
From "machine1", run:
Code:
```
ping 11.12.13.132
```

They should be able to see each other.

Now, once the IPs are properly determined and test, edit the file "/etc/hosts" as super-user in both machines and add the two lines at the end of the file:

Code:

11.12.13.14  machine1
11.12.13.132  machine2

Now, the other problem is the "machines" file you have got. It should be something like this:

Code:

machine1 slots=4 max-slots=4
machine2 slots=4 max-slots=4

Best regards,
Bruno

ahsan_smme.nust@yahoo.com · December 16, 2013, 09:05

Thank you cat, i have successfully pinged both laptops, and did all the changes you mentioned.

Code:

192.168.1.2 ahsan@ahsan-Inspiron-5521 
192.168.1.1 umer-HP-ProBook-4540s

Pinged:

Code:

ahsan@ahsan-Inspiron-5521:~/airFoil2D$ ping 192.168.1.1
PING 192.168.1.1 (192.168.1.1) 56(84) bytes of data.
64 bytes from 192.168.1.1: icmp_req=41 ttl=64 time=0.520 ms
64 bytes from 192.168.1.1: icmp_req=42 ttl=64 time=0.362 ms

My hosts file says:

Code:

ahsan@ahsan-Inspiron-5521 slots=4 max-slots=4
umer-HP-ProBook-4540s slots=4 max-slots=4

But when i run:

Code:

ahsan@ahsan-Inspiron-5521:~/airFoil2D$ mpirun --hostfile hosts -np 8 simpleFoam -parallel

ssh: connect to host umer-HP-ProBook-4540s port 22: Connection refused
--------------------------------------------------------------------------
A daemon (pid 6863) died unexpectedly with status 255 while attempting
to launch so we are aborting.

There may be more information reported by the environment (see above).

This may be because the daemon was unable to find all the needed shared
libraries on the remote node. You may set your LD_LIBRARY_PATH to have the
location of the shared libraries on the remote nodes and this will
automatically be forwarded to the remote nodes.
--------------------------------------------------------------------------
--------------------------------------------------------------------------
mpirun noticed that the job aborted, but has no info as to the process
that caused that situation.
--------------------------------------------------------------------------
mpirun: clean termination accomplished

Connection refused.

:/.
Also when i ssh from ahsan: connection timed out
While when i ssh from umer : Permission denied

wyldckat · December 30, 2013, 09:49

Hi Ahsan,

Sorry, I was not able to answer any sooner.
In summary, the problems in question are probably:

Do not use the @ symbol in the name of a machine. The one you are seeing in your command line is only implying that your user name is logged in at your machine; it does not mean that the whole text is the name of the machine.
In your case, the actual name of your machine is only "ahsan-Inspiron-5521", so you should adjust the files accordingly.
The error message is indicating that no SSH connection was possible over the port 22. You need to configure SSH for it to work on both machines: https://help.ubuntu.com/community/SSH

Best regards,
Bruno

ahsan_smme.nust@yahoo.com · January 1, 2014, 02:50

I have successfully SSH both laptops. But it gives error :

Cannot find executable s

Is it necessary for 2 laptops to have same version of ubuntu, Same openFOAM version, Same architecture (32 or 64 bit) to run a case across a network?
In our case one laptop is 32 and other 64 bit also 1 laptop has openfoam version 2.2.1 and other has 2.1.1. I think the problem lies in architecture and ubuntu version. Plz help me out on this.

wyldckat · January 1, 2014, 08:20

Hi Ahsan,

Don't expect OpenFOAM to do universal parallel processing

It doesn't matter what Ubuntu versions you have on each machine. But it does matter that you use the same exact architecture and version of OpenFOAM, as well as installed in the same path.

If one laptop is using a 32bit version of Ubuntu, then you have to install the same version of OpenFOAM and the same 32bit build, on both machines! This is because it's the common denominator between both machines, because 64bit machines can also use 32bit applications.

First choose which version of OpenFOAM you want to use and let me know, so that I can give you directions on what to do.

Best regards,
Bruno

ahsan_smme.nust@yahoo.com · February 25, 2014, 04:20

Hey wyldcat i really appreciate your help. I have successfully run an airfoil3d case on two core i 3 machines.

now i have moved to 3 machines. Actually what I did is that I installed same ubuntu(12.04 LTS) and openfoam (221) versions on all machines. Made same username and password account on all machines. All machines have same architecture. My host file looks like this:

ahsan cpu=4
alvi cpu=4
aftab cpu=4

In /etc/hosts I added these lines as you instructed:

192.168.1.2 ahsan
192.168.1.3 alvi
192.168.1.10 aftab

All machines ping and ssh successfully.
I start mpirun by typing:

mpirun -np 12 --hostfile ./hosts /opt/openfoam221/bin/foamExec simpleFoam -parallel

Now the problem is when i run my case on a single machine using its 4 cores it runs faster and reaches 200 time-steps in 5 mins 44 sec, while when I run it along 3 machines using 12 cores, it takes 10 min 33 sec. I used a hub to connect all pcs together. Decomposition method is "scotch". I decomposed my domain into 12 sub domains by typing "decomposePar" in all 3 machines. I dont know where the problem lies

. Have i given enough info? plz tell me ill provide.

wyldckat · March 2, 2014, 11:12

Hi Ahsan,

Well, throwing more CPUs at a problem doesn't mean that it will solve the problem faster. You need to take into account several details:

If all CPUs are equally powerful.
If the memory speed on all machines is the same.
If the connection between machines is powerful enough.

In addition, using Hyper-Threading isn't very good when using OpenFOAM. Therefore, if your machines are using i3 CPUs, then you should only use 2 cores on each one.

If you can describe:

The CPU model on each machine (specific model, e.g. i3-3115C);
The RAM speed on each machine, e.g. DDR3 1333 MHz;
The times that the ping command gives you, when checking the connection with the other machines;
The Ethernet connection, namely if it's 100 Mbps or 1 Gbps;
The number of cells in the mesh;

I can estimate what can be improved or if it will even work at all.

Best regards,
Bruno

ahsan_smme.nust@yahoo.com · March 4, 2014, 04:09

intel (R) Core (TM) i3-2120 CPU @ 3.30GHz 3.30GHz
Installed Memory 8 Gb
64 bit operating system,x64 based processor
ethernet connection 100Mbps
RAM DDR3 1333MHz

No. of cells in mesh 1.1 million
mesh density (150 150 10)

check the attachment for ping times.

wyldckat · March 4, 2014, 06:05

Hi Ahsan,

Quote: