> "For any OS writer, present or future, a key aspect of OS development is writing I/O (and API) performance tests, running them regularly, and immediately halting development to understand/fix the root cause -- if and when performance anomalies are detected... in large software systems, in large codebases, it's usually much harder to gain back performance several versions after performance has been lost (i.e., Browsers), than to be disciplined, constantly test performance, and halt development (and understand/fix the root cause) the instant any performance anomaly is detected..."

Yes, this! And not just OS writers, but authors of any kind of software. Performance is like a living thing; vigilance is required.