Michelle Filiba of Facebook introduced us to the challenges of mobile performance engineering at scale and the opportunities provided by detailed mobile telemetry. The Loom telemetry framework measures useful diagnostic information from production to help performance analysts investigate issues. The performance measuring system itself must be fast, so the team invested in an optimized lock-free ring buffer as the core logging mechanism. Michelle showed how engineers could enable different event providers in their traces, how the traces were uploaded to the server, and how engineers could look for performance issues in their traces. She left us with some example issues they’ve diagnosed using Loom, including delayed and extraneous network requests, and then described their plans to extend the system in the future.