Author here. I made this demo and a related matrix-matrix multiplication demo [1] back in 2015 for Robert van de Geijn's Linear Algebra: Foundations to Frontiers MOOC class [2]. In the light of Spectre attack and recent browsers' changes to reduce precision of timers, I remembered of this project, and decided to check if it still works now, 3 years later. Surprisingly, it still works well!
The source code is available on GitHub [3].
[1] https://maratyszcza.github.io/laff-demos/dgemm.html
[2] https://www.edx.org/course/linear-algebra-foundations-fronti...