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OpenCL kernel has poor scaling when amount of data is reduced by order of magnitude

Question asked by boxerab on Apr 6, 2017
Latest reply on Apr 10, 2017 by dipak

I am implementing a very serial algorithm.

The algorithm is very memory intensive.

Work item utilization is around 25% and occupancy is around 37.5 %.

There is no register spilling.


Each work item i processes N(i) bytes of data. What I am finding is that

if I reduce N(i) by a factor of 5, the kernel time only

goes down by around 20%.


What could be causing this kind of effect?  What is the best way of trouble shooting this situation?