PGI User Forum

[mleair]

Just to clarify my response above:

These messages are just warnings, but they do indicate that you may be exceeding the small memory model (which includes your total data and program text space). Try compiling and linking with the switch -mcmodel=medium. Assuming that you compile and link successfully (e.g., these warnings go away), run your program. If you get a seg fault, then you may need to increase your system stack (see the posts above).

-Mark

[Gunjan]

thank you for the help about the compiler problem....with the -mcmodel=medium the compiler is now working properly with higher resolution.....but still i have problem when im using the -mp thing in the compiler to use the both processors in the same computer....using that i can't run the code with a very high resolurion and get the segmentation fault though the memory is only half filled up.... but i can run in a lower resolution.....when i use only one processor, i can run with quite higher resolution and can use almost the full of the 4GB memory.........im working on parallelizing the code though using MPI.....but still i wonder why the -mp or -openmp is doing something like that.........thanks once again to all of u for helping me out in that one.....

[Gunjan]

im here putting one raw copy of the part of the code in which the segmentation fault occurs....in low resolution situation it doesn't give any problem, but in higher resolution only when i run in 2 processors, it gives segmentation fault right before "call clcvel" and after the end of the iteration loop on line 106......it doesn't make any sense at all to me....

[Gunjan]

i would like to add that the point in the code where it gives seg fault as described above is within the subroutine por_solve_x(ntime,fparm1) right after the 1010 loop ends and right before the call clcvel almost at the end of that subroutine.....

[mkcolg]

Looking through the code I don't see anything obvious. Typically however, seg faults that occur at a call are the result of a stack overflow error. Also, when using "-mp" all your local variables are placed on the stack, thus increasing the stack size.

When you ran this program did you explicitly set the stack size to a very large value i.e. 'unlimit'? If you did, then you might be up against your system's hard limit (unlimited stack size really does have a limit) and you may be stuck.

I noticed that the code you sent did not include any OpenMP directives so I'm a bit confused as to why your using "-mp". You must insert OpenMP directives in your code in order for the compiler to know what you want to parallelize. Our compilers do have an option called "-Mconcur" which will auto-parallelize portions of your code. However, you might still have stack issues since "-Mconcur" also puts local variables on the stack. Be sure to set the "NCPUS" enviroment variable to 2. "NCPUS" lets your program know how many processors are available for it to execute on.

For more information about OpenMP please refer to

http://www.openmp.org

Also, chapter 5 of our users guide gives some more information about openmp directives.

http://www.pgroup.com/doc/pgiug.pdf