When verbose level 4 is enabled, Blender prints kernel performance
data for Cycles on GPU backends (except Metal that doesn't use
debug_enqueue_* methods) for groups of kernels.
These changes introduce a new CYCLES_DEBUG_PER_KERNEL_PERFORMANCE
environment variable to allow getting timings for each kernels
separately and not grouped with others. This is done by adding
explicit synchronization after each kernel execution.
Differential Revision: https://developer.blender.org/D15971
2ead05d738