error when calling variables in GPU memory

When I try to call a variable stored in GPU after some calculations, the session seems to be no response.

a sample code looks like this:

a=gpuArray.rand(1e3)
for i=1:1e9
  a.^3;
end
a

Then, Matlab has no response.

I am using Ubuntu 14.04 and three GeForce 680 cards. The GPU driver is at the version 370, and CUDA is 7.5. And Matlab can recongize these three GPUs by the function gpuDevice.

Answer 1

[Joss Knight]

When you issue the command to display the variable a, MATLAB has to wait for all the one billion GPU kernel calls you have issued to finish. Did you intend to take the cube of a a billion times? or did you mean to cube each element of a, in which case you just need a = a.^3.

[Xiang Gao]

Thanks for your kind answers!

I am aware that it may take some time to display the variable a. But, in my case, it has taken for nearly one hour. So I think it might have some problem.

And the calculation about a is just an example. I did not intend to save the result.

[Joss Knight]

On my K20 GPU gputimeit tells me it takes 0.6 milliseconds to compute the element-wise cube of a 1000x1000 matrix. To do this 1 billion times therefore will take 171 hours.

I believe you have a fundamental misunderstanding here. Do you understand that your code has asked your GPU to take the cube of a million billion (1000000000000000) numbers?