| I'm actually also talking about the second. > avoid having the CPU do useless work all the time It's not worth an engineer spending 1h a year even investigating this, if it's less than 20 CPU cores doing useless work. The break even for putting someone full time on this is if you can expect them to save about fourty thousand CPU cores. YMMV. Maybe you're a bank who has to have everything under physical control, and you are out of DC floor space, power budget, or physical machines. There are other cases too. Maybe something is inherently serial, and the freshness of a pipeline's output has business value. (e.g. weather predictions for tomorrow are useless the day after tomorrow) But if you're saying that this second way of optimizing is that things should be fast for its own sake, then you are not adding maximum value to the business, or the mission. Performance is an instrumental goal of an effort. It's not the ultimate goal, and should not be confused for it. |
Then there are interactive programs. With a human potentially waiting on it. Someone's whose time may be just as valuable as the engineer's time (morally that's 1/1, but even financially the difference is rarely more than a single order of magnitude). If you have as few as 100 users, shaving off seconds off their work is quickly worth a good chunk of your time.
Machine time is cheap, but don't forget that user's time is not.