[parsec-users] Porting Bodytrack on GP-GPUs -- Problems and Issues

aftab hussain aftab.hussain at seecs.edu.pk
Tue Aug 9 03:16:08 EDT 2011

Dear All,
             I am trying to port Bodytrack application to GP-GPUs as my MS
thesis. I have a working code but my tracking results are screwed.
When I further investigated the code I found that the difference in sin/cos
calculations on CPU and GPU are messing things up.
For some particles the difference (error uptill 6th-7th decimal place) in
sin/cos calculations gets accumulated in later stages
(Body Geometry calculations, projection calculations, Error term
calculations). In the edge error term calculations I get one extra
sample point due to which the error weight gets changed and the final
normalized weight for that particular particle is different
upto 4th decimal place (a lot of error). And this is in the Initialization
stage of the particle filter (weight calculation).

This in turn produces error for the next iterations because in the particle
generation stage for the next iteration, a wrong particle is
selected which further introduces error and finally the estimate for a frame
is very different from the CPU estimate.

I have the following stages implemented on GPU because these are the most
compute intensive stages of the application.

1- Body Geometry
2- Projection Calculation
3- Error Terms (Inside Error Term, Edge Error Term)

When I move the sin/cos calculation to CPU, the improvement in execution
time I get on the GPU stages in screwed up by the particle generation
stage because I have to arrange (copy from CPU data structure to GPU data
structure plus sin/cos calculation) the data structure suitable for GPU
implementation that gives speed up in the execution. The overall application
speed up is not very interesting due to this problem.

Can any help me in this issue because my Thesis is stuck due to this

Best Regards

Aftab Hussain
Research Assistant,
High Performance Computing Lab,
NUST School of Electrical Engineering and Computer Science
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