Waterfall display might work though, or coloured sequences give each function it’s own colour then draw the last stack as a pattern of colours, humans are really good at spotting anomalies in patterns, probably because tree,tree,tree,wolf,tree was useful to our ancestors.
This was common in home computers that could run a routine at every VBL (Vertical Blanking) interrupt, often chosen as the main timing 'tick' interrupt. Change the overscan border color for each part of the subroutine, and the timing gets reflected quite directly in the colored fringes that are displayed as the program executes.
