Procrastination time: what does this mean?

I am supposed to be writing some more stuff for my PhD thesis, but this feels like a more legitimate way to procrastinate than others…

I have plotted the performance of a model of a multi-core processor system and, because it was something to do, applied a Fourier Transform to the data (the black plots in first chart):

2k LRU performance

So, my question is, what does the second chart mean? If it means anything of course.

I get that the real component is plotted on the x-axis and the imaginary component on the y-axis, but is there any information conveyed in the chart?