It's plotting the relative speedup of each router's benchmark vs the slowest benchmark on that dataset. (For example, Beego's performance on the GithubStatic dataset was 12 times faster than the slowest GithubStatic dataset performance)

Fastest overall routers are sorted left to right. Keep in mind that the vertical scale is logarithmic, so implementations on the left are more than 100 times faster than those on the far right.