MPI and OpenMPI

[Rahman]

Hi everybody,
I want to run FDS with multiple mesh on more than one core on a my laptop.I read the User’s Guide but I'm confused and don't know exactly what to do now.

My laptop have four core(two physical and two virtual).

Please help me exactly what to do.
Sorry for my poor English.

[Dave McGill]

Hi Rahman,

The first step would be to open a Command Prompt window and type the following.

mpiexec -n 4 fds job_name.fds

Dave

[Kevin]

You need to be more specific. What do you not understand, exactly. I wrote much of the User's Guide sections on parallel processing, so if you do not understand it, I want to know what specifically do you not understand.

[Dave McGill]

To expand on my earlier response. I should have said.

1. open a Command Prompt window

1. use DOS commands to navigate to the folder with the fds input file (job_name.fds)
2. type, "mpiexec -n 4 fds job_name.fds"
3. press Enter

[Rahman]

Thanks dave for your attention.
I did the things that you said  but I was faced with the following error:
"
ERROR: The number of MPI processes,      4, exceeds the number of meshes,      2
 (CHID: tangential_velocity)
Attempting to use an MPI routine after finalizing MPI

ERROR: The number of MPI processes,      4, exceeds the number of meshes,      2
 (CHID: tangential_velocity)
Attempting to use an MPI routine after finalizing MPI

ERROR: The number of MPI processes,      4, exceeds the number of meshes,      2
 (CHID: tangential_velocity)
Attempting to use an MPI routine after finalizing MPI

ERROR: The number of MPI processes,      4, exceeds the number of meshes,      2
 (CHID: tangential_velocity)
Attempting to use an MPI routine after finalizing MPI  "

[Dave McGill]

Rahman,

I (incorrectly) assumed you had 4 meshes.

Try,

mpiexec -n 2 fds job_name.fds

Dave

[Rahman]

Dear Dave,

I have a few other questions.
For example, for a dual-core machine how many "MPI_PROCCES"  can to be created? in other words,in expression " mpiexec -n A fds job_name.fds "  number A to what number can be increased for this dual-core machine ??

[Cian Davis]

Hi Rahman,

For best results, you should not run more MPI processes than you have physical cores on your machine. For example, Intel i7s often have hyperthreading, so 4 cores show up as 8 - our tests have shown best performance when the number of MPI processes does not exceed 4 (Either 1 job with 4 MPI processes, or 2 jobs with 2 processes each).

For a dual core machine, in your example, A should not exceed 2.

Regards,

Cian

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[Rahman]

Thanks alot Cian Davis, Your explanations was excellent.

another one question:
How many threads can I set for dual core machine ??
I do not understand What is the thread ??

[Kevin]

Here is a very brief explanation of the various components of multi-processing hardware.

https://kb.iu.edu/d/avfb