Rodinia GPU Benchmark
backprop
vp-opt1: value_pattern - single zeros
backprop_cuda_kernel.cu: 81. The delta array has many zeros. We can check each entry on the GPU side to execute a special branch that avoid computation.
vp-opt2: data_flow - duplicate values
backprop_cuda.cu: 180. net->input_units is copied to GPU at Line 118 and copied back at Line 188. Meanwhile, both the GPU data and the CPU data are not changed. As a result, the copy at Line 188 can be eliminated safely.
bfs
vp-opt1: value_pattern - type overuse
kernel.cu: 22. The g_cost’s array’s values are within the range of [-127, 128). We can specify this array’s type as int_8 instead of int to reduce both kernel execution time and memory copy time.
vp-opt2: value_pattern - frequent values
bfs.cu: 107-109. Accesses to these arrays showing a frequent value pattern where zeros are read most of the time. We can replace the memory copies of all zeros from CPU to GPU by memset that is much faster to reduce memory copy time.
cfd
vp-opt1: value_pattern - frequent values
euler3d.cu: 173. The cuda_initialize_variables function writes values in a frequent value pattern. We can hash the accessing index of this array to limit memory access in a certain range and increase cache locality. Since this array is changed in the second iteration, this optimization only applies to the first iteration.
vp-opt2: data_flow - redundant values
euler3d.cu: 570. The old_variables array is originally initialized at Line 551 with the same values are variables but copied again at Line 570. We can safely eliminate the second copy which is redundant to the first iteration.
hotspot
vp-opt: value_pattern - approximate - single value
hotspot.cu: 164. The temp_src array contains many very close floating point numbers.
Using the approximate mode, gvprof determines values in this array are approximately the same under a certain approximation level.
Therefore, we can read just some neighbor points on Line 195 and still get similar final results.
hotspot3D
vp-opt: value_pattern - approximate - single value
opt1.cu: 29. Like the hotspot example, the tIn array contains many very close floating point numbers. And gvprof determines all this values in this array are approximately the same under the certain approximation level. Incontrast to the hotspot example that selectively choose neighors, we use loop perforation to compute half of the loops and get similar result.
huffman
vp-opt: value_pattern - frequent values
his.cu: 51. GVProf reports frequent values for the histo array in both the write and read modes. Because the most frequently updated value is zero, we can conditionally perform atomicAdd to reduce atomic operations.
lavaMD
vp-opt: value_pattern - type overuse
kernel_gpu_cuda.cu: 84. The rA array contains only few distinct numbers. By checking its initialization on the CPU side, we note that there are only ten fixed values within 0.1 to 1.0. We can store these values using uint_8 instead of double, saving 8x space. These values are then decoded on the GPU side. In this way, we trade in compute time for memory copy time.
pathfinder
vp-opt: value_pattern - type overuse
pathfinder.cu: 144. The gpuWall array’s values for this input will be within [0, 255], thereby we can use uint8_t to replace int to reduce global memory traffic.
srad
vp-opt1: value_pattern - heavy type
srad_kernel.cu: 79. d_c_loc is always one or zero. We changed the value type of this array to bool.
vp-opt2: value_pattern - structured
srad_kernel.cu: 38 . d_iN, d_iS, d_jW, d_jE are used to indicate the adjacent nodes’ coordinates which have structured patterns. We removed these four arrays and replace them with the corresponding calculations.
streamcluster
vp-opt: data_flow - redundant values
streamcluster_cuda.cu:221. These arrays center_table_d, switch_membership_d, p are not changed in each iteration. Therefore, we can use flags on the CPU to detect if these arrays will be changed and only copy values if they are.