> Don't tune for speed until you've measured, and even then don't unless one part of the code overwhelms the rest.

Genuine question, is software performance really linear like that, that one can and should only fight the tightest bottleneck, one workload at a time? Never really sounded right.

It also sounds like the typical sleight of hand where the difficult bit is simply laundered a layer up, in this case the choice of what workload one investigates.