Implementation of sum of two vectors using MPI.
I've added generated output.csv file with size of vectors, number of processes and run-time.
Here is command to run it, if you use Linux:
for j in 2 4 8 12 16 24; do for i in `seq 3`; do /usr/bin/mpirun -np $j /your/path/to/project/cmake-build-release/MPI >> output.csv; done done| Size | Processes | Run-time |
|---|---|---|
| 200000000 | 1 | 1.3044 |
| 200000000 | 1 | 1.3092 |
| 200000000 | 1 | 1.2215 |
| 200000000 | 2 | 2.3942 |
| 200000000 | 2 | 2.4517 |
| 200000000 | 2 | 2.3716 |
| 200000000 | 4 | 3.2577 |
| 200000000 | 4 | 2.6539 |
| 200000000 | 4 | 2.3973 |
| 200000000 | 8 | 2.3643 |
| 200000000 | 8 | 2.5601 |
| 200000000 | 8 | 2.5600 |
| 200000000 | 12 | 2.4458 |
| 200000000 | 12 | 2.5164 |
| 200000000 | 12 | 2.5755 |
| 200000000 | 16 | 3.4011 |
| 200000000 | 16 | 3.2230 |
| 200000000 | 16 | 2.8996 |
| 200000000 | 24 | 3.1183 |
| 200000000 | 24 | 3.1636 |
| 200000000 | 24 | 3.1457 |
As you see, we haven't got speed acceleration, parallel version working longer than sequential. That's because cost of MPI_Gather/MPI_Scatter operations bigger that cost of sum.
But if we change sum to another function we can get better results of parallel optimizations. So I choose such function:
double f(double a, double b) {
if (a > b) {
return sqrt(a) + cbrt(b);
}
return cbrt(b) + sqrt(a);
}And now get better results:
| Size | Processes | Run-time |
|---|---|---|
| 200000000 | 1 | 10.9111 |
| 200000000 | 1 | 10.7411 |
| 200000000 | 1 | 9.9409 |
| 200000000 | 2 | 8.0377 |
| 200000000 | 2 | 9.7273 |
| 200000000 | 2 | 7.4046 |
| 200000000 | 4 | 5.3152 |
| 200000000 | 4 | 5.3474 |
| 200000000 | 4 | 4.8490 |
| 200000000 | 8 | 3.7550 |
| 200000000 | 8 | 3.7938 |
| 200000000 | 8 | 3.5647 |
| 200000000 | 12 | 3.6919 |
| 200000000 | 12 | 4.4344 |
| 200000000 | 12 | 3.4221 |
| 200000000 | 16 | 4.2836 |
| 200000000 | 16 | 3.9359 |
| 200000000 | 16 | 3.9416 |
| 200000000 | 24 | 4.0231 |
| 200000000 | 24 | 3.8237 |
| 200000000 | 24 | 3.8215 |
So now we see better results, because new function not so easy, and cost of it bigger that simple sum.
OS: Ubuntu 16.04.
Processor: Intel® Xeon(R) CPU X5650 @ 2.67GHz × 24.