A performance profile is a particular type of plot popular in optimization. Basically, for each ratio R on the x axis, the y axis shows what is the fraction of the number of total tests that were solved within a ratio R of the best result, under a certain performance measure. See for instance this blog entry for an introduction, or Section 22.4 of Higham and Higham's book Matlab guide.
For instance, in the picture below, the blue algorithm gives the best result on about 95% of the examples, and solves the remaining ones within a factor of about 1.2 of the best algorithm.
What is the clearest way to label the axes of such a plot?
I have included an attempt above, but it might be too verbose for a label. The linked blog uses "problems solved" and "performance ratio". Higham and Higham use no axis labels. Other sources put unenlightening letters such as $\theta$ on the x axis.