Is there a 'top' like command for monitoring the GPU and memory usage of a video card? I am most interested in Linux commands, but and OS would be interesting.

I strongly suspect that for a group of my systems the video cards are being under-utilized (but I have no idea by how much) and would like to re-allocate funds to other bottle-necks. We are using higher end cards, so the price difference between cards is significant.

Thank you.