[kasey_junk]

I disagree completely with your 80% number. I haven't worked on a project that had 0 performance work ever.

Performance is a first class design constraint just like development time, budget & functionality, if you don't treat it as such from the beginning you are asking for trouble.

[breischl]

But different parts of a project usually have different performance goals. Typically just the important/frequently used parts need to be optimized. Infrequently used things (maybe setup, admin interface, options dialog) can usually just be "good enough."

So one could say that within a project, 80% of the code isn't performance critical.

[kasey_junk]

All parts of a system have performance requirements. Some of them you might meet naively, great!

But if you don't know what they are it is very hard to back into acceptable performance.

[breischl]

No kidding. Who ever said anything about not knowing what the requirements are?

The point you were disagreeing with here was "80% of the software an engineer will write will not require optimization". ie, 80% of any given system hitting the performance requirements naively. So... why are you still arguing?

[kasey_junk]

Because blind adherence to the "Make it work then make it fast" advice has been the bane of my career.

Generally speaking, I have not found it to be true that you can make something fast if you didn't think about performance first. If you thought about it, and came to the decision "it will be fast enough no matter what we do" bully for you, but for me that happens way less than 80% of the time.