[Trilinos-Users] Using OpenMP support in Trilinos

[Eric Marttila]

Mike,
The problem size is 1 million unknowns.  I have Trilinos compiled with MPI 
enabled.  However, I'm launching my program with only one MPI process.

Here is some system information:
Processors:  Dual Intel Xeon E5645 Hex-Core / 2.4 Ghz / Cache: 12MB 
RAM: 96 GB
OS: CentOS 6.2 64bit.  

When solving for 1 million unknowns on this system, AztecOO reports the 
following solution times:

Solution time: 3.3 seconds   (using Trilinos with OpenMP disabled)
Solution time: 4.0 seconds   (using Trilinos with OpenMP enabled)

I had OMP_NUM_THREADS set to 4.

If I set OMP_NUM_THREADS to 1 then I get 3.3 seconds in both cases.

Thanks for your help.
--Eric

On Wednesday, September 19, 2012 08:48:20 pm Heroux, Michael A wrote:
> Eric,
> 
> Can you give some details about problem size, use of MPI (or not), type of
> system, etc.
> 
> Thanks.
> 
> Mike
> 
> On Sep 19, 2012, at 3:17 PM, Eric Marttila wrote:
> > Hello,
> > 
> > I'm using AztecOO and ML to solve a linear system.  I've been running my
> > simulation in serial mode, but now I would like to take advantage of
> > multiple cores by using the OpenMP support that is available in
> > Trilinos.  I realize that the packages I'm using are not fully
> > multi-threaded with openmp, but I'm hoping for some performance
> > improvement since some of the packages I'm using have at least some
> > level of OpenMP support.
> > 
> > I reconfigured and built Trilinos 10.12.2 with
> > 
> > -D Trilinos_ENABLE_OpenMP:BOOL=ON
> > 
> > ...but when I run my simulation I see that it is slower than if I have
> > Trilinos configured without the above option.  I have set the environment
> > variable OMP_NUM_THREADS to the desired number of threads.
> > 
> > I was also able to reproduce this behavior with one of the trilinos
> > example prgrams (attached below), so I suspect I am missing something
> > obvious in using the OpenMP support.
> > 
> > Does anybody have thoughts of what I might be missing?
> > 
> > Thanks.
> > --Eric

-- 
Eric A. Marttila
ThermoAnalytics, Inc.
23440 Airpark Blvd.
Calumet, MI 49913

email: Eric.Marttila at ThermoAnalytics.com
phone: 810-636-2443
fax:   906-482-9755
web: http://www.thermoanalytics.com
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