SIMD and Other Rabbit Holes

Last week I read this post by Mitchell Hashimoto arguing that everyone should know SIMD. It reminded me of how I ran into it myself. Most engineers have no reason to touch complex CPU instruction sets unless they work on something performance sensitive, like building a database or processing images. My own exposure happened by accident, because someone at Mixpanel had the brilliant idea of nerd-sniping engineers into what we called a “perf challenge”.At Mixpanel, we built a columnar database from scratch to answer product analytics queries, well before something like ClickHouse became commonplace. Performance was a big part of why the product was popular, and the team that built it could not resist a hard problem.The format of the perf challenge was simple. Take a problem that is trivially easy to get correct but brutally hard to make fast, and timebox it to a couple of weeks, small enough that a weekend of work made you competitive. The 2017 problem was a one liner. Given a file of…