[fds-smv] FDS - Multiple Processor Version

[Pai]

Dear All,

I am trying to run a parallel version of FDS on my computer which has
8 processors. It is running too slow. I am just wondering whether I
have to invoke MPICH2 explicitely. I know its installed in my
computer.

I went through page 11 of user manual but it does not say how to run
the simulation on a single computer with multiple processors. I have a
very large geometry (125x30x20) and my current grid size is 0.175m. I
am unable to reduce it further.


I have 8 meshes and I have run the file on a command prompt using the
normal method.

Can anyone say whats wrong with my input, if any?

Regards,
Arun

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[Kevin]

Your mesh is not big. If you run an MPI job on a single computer, you
will use all the processors, but you may not speed things up as much
as you think. There is still the bottleneck of getting data in and out
of your single memory (RAM). If you do not have to use multiple
meshes, consider the OpenMP version of FDS. There is some explanation
in the discussion thread that is listed near the top of the list.

[Pai]

Kevin,

Thanks for the response. May I know what is the maximum number of
cells a 2gb processor can handle?

With a mesh size of 0.35m for my entire geometry, I landed up with
almost 2 million cells. But I am not happy with the temperatures that
I am getting (only 350 degree celsius). I could not refine my mesh
further and hence had to use the master computer with 8 processors to
run the multiple mesh version.

[Deepak]

For using multiple processor on quad core or 8 core machines, please follow the below steps:

• Install FDS first
• Install MPICH2 with dot net frame work
• then set the environmental variables for MPICH2 & FDS
• then remove all the windows securities (i.e firewall and give access to the folders(sharing) that you are using)
• Then restart the computer ( while running the parallel jobs just disable the network, because if the network goes in between while running the job, then your FDS simulation will stops)
• And type this command to run in 8 processors in command prompt: " mpiexec  -n  8  FDS5_mpi  jobname.fds ", make sure that your mesh is divided in to 8 meshes.

Hope this will be helpful.

Best Regards

Deepak

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[Pai]

Thanks for the info Deepak. But what does 'environmental variables for
MPICH2' mean?

I tried using *mpiexecn, but the error says it cannot recognise the
command.

[Deepak]

Environmental variables for MPICH2 menas:

Right click on the my computer, then click advanced, then you will find environment variables, click on it and under system variables you will find path, just edit the path and put this extra text ";C:\programfiles\MPICH2\bin;" then click ok,ok,ok buttons. Done.

here "C:\programfiles\MPICH2" is the installation directory for MPICH2.

then type the command as mentioned in my previous email, it should work.

Best Regards
Deepak

[revanth krishna]

Dear pai,

I tried using *mpiexecn, but the error says it cannot recognise the
command.

it should be (red color text), mpiexec[space]-n[space]no.of processors[space]fds5_mpi[space]filename.fds

no.of processors (should be numerical) depends on no of meshes/no of cores of your PC
 
rest follow the steps as said by Deepak...

Thanks & Regards,
Revanth

[Pai]

All,

Thanks for the responses. My doubt is, can the MPI version be used for
running multiple meshes on a single computer? For example, I have 8
processors and 8 mesh, can the MPI version be used?

Each of my mesh has 2 million cells so in all the input file has 16
million cells.

Thanks.

[Deepak]

Yes you can use, but if you use all 8 processors, your system might be overloaded, so you might not be able to open the smokeview to visualize your results. 

So, I will suggest you to use only 6 processors for running the FDS, then you would be able to open your smokeview without any overload of the computer.

Best Regards

Deepak

[Pai]

Deepak,

Thanks for the response. And is the procedure the same as the one you
described above?

It looks like the whole system is running dead slow. I checked whether
all the processors were working and yes, it does. May I know the
reason for that?

Can you also tell me approximately how many cells can a single
processor take?

Regards,
Arun

[Michele]

Hi Arun,

I also run simulations on a single machine with a quad-core dual-processing processor.

The best way to run it and use all CPU power is to run the simulation with the command

mpiexec -channel ssm -n 8 -localonly fds5_mpi jobname.fds

The -localonly eliminated some error messages, and the -channel ssm improves the CPU usage. Do some test with and without it, I noticed the CPU usage is always at 100% with -channel ssm command.

With a 2GB RAM, as a rule of thumb consider 1mio cells per mesh.

Bye,

Michele