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BOLT (Meta Binary Optimizer)

BOLT (Binary Optimization and Layout Tool) is Meta's open-source post-compile binary optimiser that rewrites an already-compiled binary using runtime profile data. Published as "BOLT: A practical binary optimizer for data centers and beyond" (CGO 2019). Part of LLVM: github.com/llvm/llvm-project/tree/main/bolt.

Role on this wiki

• The post-compile-time consumer in Meta's fleet-scale FDO pipeline. Continuously-collected LBR profiles from the Strobelight LBR profiler are turned into FDO profiles consumed by:
  • Compile time — CSSPGO (Context-Sensitive Sample-based Profile-Guided Optimization) in LLVM.
  • Post-compile time — BOLT, which rewrites binaries in-place.
• Capacity impact: on Meta's top 200 largest services, the combined pipeline delivers "up to 20% reduction in CPU cycles, which equates to a 10-20% reduction in the number of servers needed to run these services at Meta." This is the economic datum that pays for Strobelight as a platform.

Seen in

• sources/2025-03-07-meta-strobelight-a-profiling-service-built-on-open-source-technology — named as the post-compile consumer of LBR-derived FDO profiles.

Related

• systems/strobelight — the upstream profile producer.
• patterns/feedback-directed-optimization-fleet-pipeline — the pattern BOLT sits at the tail of.
• companies/meta