University of Pennsylvania, CIS 565: GPU Programming and Architecture
- Alex Fu
- Tested on: Windows 10, i7-10750H @ 2.60GHz, 16GB, GTX 3060 6GB
I use the average FPS over 1-11 secs to represent the performance of the application. I have tested the impact on performance by the boids number, CUDA block size, grid cell size, and the searcing volume.
CUDA block sizes are all 128.
The boids number is 500,000 for scattered and coherent grids, and 20,000 for brute force.
The boids number is 500,000 and the CUDA block size is 128.
| Cell Width | Cell Number | Average FPS |
|---|---|---|
| 10 | 10648 | 157.8 |
| 15 | 2744 | 59.0 |
| 20 | 1728 | 23.0 |
| 40 | 216 | 7.1 |
| 80 | 64 | 1.7 |
Tested in coherent grids. The CUDA block size is 128.
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For each implementation, how does changing the number of boids affect performance? Why do you think this is?
- Generally, the more boids there are, the slower the program runs. However when boids are less than 20,000 this is contrary when using uniform grids — I guess it's because the boids are too scattered so the program will go over nearly every grid. Under that circumstance the I/O to the memory is close to the brute force and plus the extra
if...else...branches, the performance may be worse than brute force.
- Generally, the more boids there are, the slower the program runs. However when boids are less than 20,000 this is contrary when using uniform grids — I guess it's because the boids are too scattered so the program will go over nearly every grid. Under that circumstance the I/O to the memory is close to the brute force and plus the extra
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For each implementation, how does changing the block count and block size affect performance? Why do you think this is?
- To be honest, I haven't found any specific relation between block size and performance. But one thing for sure is that the size of 32 is the most disadvantageous to the performance on my machine.
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For the coherent uniform grid: did you experience any performance improvements with the more coherent uniform grid? Was this the outcome you expected? Why or why not?
- Yes. If there are less uniform grids, which means the size of cell is larger, I believe the program will have to check more boids and the performance will get closer to the brute force.
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Did changing cell width and checking 27 vs 8 neighboring cells affect performance? Why or why not? Be careful: it is insufficient (and possibly incorrect) to say that 27-cell is slower simply because there are more cells to check!
- Checking 27 neighboring cells is actually significantly faster than chekcing 8 neighboring cells. I think it's because: 1. when checking 27 neighboring cells, the cell width can be the half of those when checking 8, thus the search volume decrease to 0.421875 of the origin volume; 2. when checking 27 neighboring cells, there will be less
if...else...branches (and it's more possible that all threads are in the same branch); recalling the knowledge ofwarp, branch statements will harm the performance. - Besides, checking 27 cells is much easier to code.
- Checking 27 neighboring cells is actually significantly faster than chekcing 8 neighboring cells. I think it's because: 1. when checking 27 neighboring cells, the cell width can be the half of those when checking 8, thus the search volume decrease to 0.421875 of the origin volume; 2. when checking 27 neighboring cells, there will be less
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There is an unsolved bug in coherent grids when boids size is small. See my post in Ed Discussion.
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At first all my boids would disapear quickly. It took me a while before I realize it's because some values were divided by zero.