I have a scenario in which a sphere rolls inside an arc tube similar to the picture:

The radius of the sphere is a bit smaller than the side of the square that makes its sides. In Bullet, I've set up the arc as a static trimesh, part of a bigger trimesh that represents the environment in which the sphere rolls on.
When the sphere rolls inside the arc, CPU consumption raises dramatically. When over any other part of the trimesh surface, the performance is good, as most of it is quite simple. Even if it rolls against the outside part of the tube there is no considerable performance drawback.
How could I improve performance? Would that be a case for convex decomposition of the arc?
Thanks in advance,
Krones