parallel work of GPU & CPU Is it possible

Is it possible to run some task on the GPU, while the CPU works on another? This tasks could be absolutely different.
I’ve tried to run Super_PI & cuda kernel – while kernel is running other programs couldn’t do anything, so there is another question, what does the main stream (which runs cuda kernel) do, while the kernel is running?

And by the way is there any opportunities to avoid 5s limit on kernel running time?