Modernizing the Meta Ads Service With an Open-Source Kernel Scheduler

What this post added

This post details the modernization of the Meta Ads Service by implementing a custom scheduling policy using sched_ext, an open-source, BPF-based extensible scheduling framework. This was done to address latency regressions caused by a Linux kernel upgrade and to optimize the Ads delivery workload. The custom policy soft-partitions CPUs, prioritizes latency-critical threads, and dynamically adjusts pool sizes based on load, improving L3 cache locality. The implementation resulted in a 28% reduction in ads retrieval stage p99 latency, 3.28 MW power savings, and a 1.1% increase in ads ranked. The post also highlights the benefits of sched_ext as a parallel optimization path, enabling independent deployment of scheduler improvements as user-space BPF program updates, and its upstreaming into Linux for broader ecosystem use.