Is asking a question that fewer than 1% of applicants "can even get the basics correct" -- which implies that only a tiny fraction of 1% actually provide a fully complete and correct answer -- a good use of either the applicants' or the interviewer's time? Is it effective in distinguishing candidates, or are you only seeking 1 success (fewer, actually) per 100?
1% success rate is typical when interviewing developers.
Also they get asked multiple exercises, not doing great at one is not eliminatory.
Being able to quickly identify whether an individual is exceptionally good is very important to ensure the employer can fast-track them and be responsive quickly enough that he doesn't accept another offer.
cpu cache line optimization is relevant to a superminority of programming contexts
if you're working in those contexts then it's all fine, but it's important to acknowledge that most software development is bottlenecked by concerns far above this level of concern
