Project 1 - Flocking Simulation

University of Pennsylvania, CIS 565: GPU Programming and Architecture, Project 1 - Flocking

• Weiqi Chen
  • LinkedIn
• Tested on: Windows 10, i7-8750H @ 2.20GHz 2.21GHz, 16GB, GTX 1050 2GB

Screenshots

5,000 Boids	100,000 Boids

Performance Analysis

1. Number of Boids

The plot shows the FPS vs Boid Size for the 3 implementations.

• As the number of boids increases, performance decreases for all implementations.
• Coherent grid has the best performance with large number of boids.
• Visualization decreases performance.
• The improvement from uniform grid to coherent uniform grid is more obvious as the number of boids increases.
• The naive method is only good with a small number of boids.

For each boid, naive method requires us to check every other boid, while uniform grid methods only need to check some/all of a boid's neighboring cells. Therefore computation time is decreased.

2. Block Size

The plot below shows the FPS vs block size and visualization is turned off.

• Performance is increased significantly when block size is increased from 16 to 32.
• From block size 32 to 256, the performance is similar. Since the warp size is 32, a block size of less than 32 will lead to inactive threads in a warp. When block size is greater than 32, all threads will be used for parallel computation.

3. Coherent Uniform Grid

Coherent uniform grid has better performance than uniform grid. The more boids there are, the greater the difference. This is because:

• We reorder dev_pos and dev_vel and boids in the same cell now occupy contiguous memory.

• dev_particleArrayIndices in the global memory is accessed one time less, resulting in 1 level decrease of indirection.

4. Cell Width

Half cell width increases the performance due to decrease in computation. Assuming a neighborhood distance of 1:

• For full cell width, 2, need to check a volume of 4³ = 64
• For half cell width, 1, need to check a volume of 3³ = 27

Using the coherent uniform grid implementation, we have:

	Full Width (8 cells)	Half Width (27 cells)
5k Boids	1431 FPS	1521 FPS
15k Boids	1011 FPS	1132FPS
50k Boids	547 FPS	556 FPS