Interesting visualization, but it may be a tiny bit misleading. My first thought was that the larger the horizontal bar, the more time spent in that function, but that's not the case. Rather, it captures the number of times the function was seen in some execution path.

So if you have:

    f():
        do_less_work()
        do_large_work()

f()'s width is inflated even though it's do_large_work() that does most of the work.

The actual execution time of a function is its xwidth less the sum of all its childrens' xwidths.