We are running a simple code doing random reads and sequential write (i.e. gather operation) on both the CPU and GPU part of the I7-4770R (separately, one at a time) and experiencing 4x slower performance on the GPU compared to the CPU. When doing sequential reads and writes and even random writes, the performance is very similar indicating that both the internals of the chip as well as the memory controller allows the GPU to access the DRAM with the same speed the CPU does. However have no idea why random reads suffer a 4x performance penalty and this limits our application’s performance quite a lot. Would be good to know what the reason of this performance difference is and see whether there is some remedy for it.
Here are also the numbers from our experiments. The metric is execution time, so the lower the better.
MAP
REDUCE
GATHER
SCATTER
Intel i-4770r IrisPro-16G mem-4 Cores-OpenMP-CPU
24.73
13.65
36.34
231.67
Intel i-4770r IrisPro-16G mem-40 EU-OpenCL-GPU
23.55
16.29
167.03
270.7