The GPU-CPU transfer rate seems to be much below I would expect from an HD 5470, with 512 DDR3 memory!
I am trying to copy memory from the GPU to the CPU using Ogre RenderTexture class with Direct3D9. I tried different texture sizes, and for each, I executed the copy operation 10,000 times to have accurate measurements. Here are the results I got:
Those seems to be much less than I would expect from a Mobilitiy 5470 HD with 512 MB DDR3 on an Intel i5 processor! Actually, I read a post written some 4 years ago (2007) and it claimed that GPU-CPU using OpenGL PBOs is around 1.3 GB/sec: