The purpose of this programming assignment is to gain experience in writing OpenMP programs. You will start with a working serial program (quake.c) that models an earthquake and add OpenMP directives to create a parallel program.
The goal is to be systematic in figuring out how to parallelize this program. You should start by using the gprof profiling tool to figure out what parts of the program take the most time (to use gprof, you will need to compile your program with the -pg argument). From there you should examine the loops in the most important subroutines and figure out how to add OpenMP directives. The program will be run on a single compute node of the deepthought2 machine.
To compile OpenMP we will be using gcc version 4.8.1 (the default version on
deepthought2, which you can get by doing module load gcc on the deepthought2
login node), which nicely has OpenMP support built in. In general, you can
compile this assignment with:
$ gcc -fopenmp -pg -o quake quake.c -lm
The -fopenmp tells the compiler to, you guessed it, recognize OpenMP directives. -lm is required because our program uses the math library. -pg needs to be added to collect profiling data when the program is run; you can remove this option before you do final performance testing.
The environment variable OMP_NUM_THREADS sets the number of threads (and presumably processors) that will run the program. Set the value of this environment variable in the script you submit the job from. It defaults to using all available cores, and on a deepthought2 node that means 20.
Quake reads its input file from standard input, and produces its output on standard output. Quake generates an output message periodically (every 30 of its simulation time steps), so you should be able to tell if it is making progress.
When the program runs correctly, all versions (serial or parallel) running the
quake.in input, irrespective of the number of threads used, should output this
at the 3840th timestep:
Time step 3840
5903: -3.98e+00 -4.62e+00 -6.76e+00
16745: 2.45e-03 2.66e-02 -1.01e-01
30169 nodes 151173 elems 3855 timesteps
This is the output for quake.in.short:
Time step 30
978: 8.01e-03 7.19e-03 8.41e-03
3394: -3.69e-21 1.57e-20 -5.20e-20
7294 nodes 35025 elems 34 timesteps
You should submit your program and the times to run it on the input file quake.in (for 1, 2, 4, 8 and 16 threads). Since quake runs for a while on this input dataset for small numbers of threads, quake.in.short is another input file that runs for much less time (you can use this for testing). To time your program, use omp_get_wtime() by placing one call at the beginning of main (next to the omp_get_max_threads call) and another one toward the end of main (before the "Done. Terminating the simulation" print statement).
You also must submit a short report about the results (1-2 pages) that explains:
The project will be graded as follows:
| Component | Percentage |
|---|---|
| Runs correctly with 1 thread | 10 |
| Runs correctly with 16 threads | 40 |
| Performance with 1 thread | 10 |
| Speedup of parallel version | 20 |
| Writeup | 20 |