Ask HN: Looking for a Talk on Software Optimization

There was some academic research mentioned, I don't know exactly when, on HN related to software optimization. I can't seem to track down the source and need some help. From what I can remember, the gist is this:

- How do you know your optimization is useful?

- It could be fragile, dependent on compilers, etc.

- Modelling in this research was done by modifying a concept of time. Something like assuming some subsystem ran faster using some sort of novel technique I can't recall.

- Instrumentation within this framework gave data that pointed to subsystems where optimization would be fruitful and avoid fragility.

I can't be sure if any of the details of the above points are misremembered. Sorry. Hopefully someone can help.