Adding CPU affinity in a 24-core build machine made builds take longer
A developer's experiment with CPU affinity on a 24-core build machine produced counterintuitive results: builds took longer. The account, shared on Lobsters and hosted on infosec.exchange, details how pinning processes to specific cores, a technique often used to improve cache locality and reduce context switching, instead degraded performance. The author, David Chisnall, observed that the build times increased when CPU affinity was applied, suggesting that the default scheduler's dynamic load balancing was more effective than a static assignment. The post does not specify the exact build system or the magnitude of the slowdown, but the anecdote serves as a cautionary tale for developers considering affinity tweaks on high-core-count machines. The source is a single post with comments, so the information is limited to the author's experience and the ensuing discussion.
CPU affinity can hurt performance on multi-core builds, so developers should test before assuming it helps.