docs(audits): profile parallel signature computation scaling (#1085)#3943
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Replace the prior scaling audit with a concise plan focused on empirically locating the parallel signature path's thread-count ceiling. Document the parallel.rs entry points, frame the compute-bound versus memory-bandwidth-bound question, specify a criterion bench across 1/2/4/8/16 threads with 4K/8K/16K block sizes, predict saturation around 8 threads on commodity DDR4, and recommend capping rayon workers and renaming the threshold env override to PARALLEL_SIGNATURE_THRESHOLD.
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May 18, 2026
…3943) Replace the prior scaling audit with a concise plan focused on empirically locating the parallel signature path's thread-count ceiling. Document the parallel.rs entry points, frame the compute-bound versus memory-bandwidth-bound question, specify a criterion bench across 1/2/4/8/16 threads with 4K/8K/16K block sizes, predict saturation around 8 threads on commodity DDR4, and recommend capping rayon workers and renaming the threshold env override to PARALLEL_SIGNATURE_THRESHOLD.
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Summary
crates/signature/src/(parallel.rs, layout.rs, block_size.rs) and cross-reference the SIMD batching landed under Rename local copy partial directory setter #1024.MAX_SIGNATURE_THREADSplus renaming the env override toPARALLEL_SIGNATURE_THRESHOLD.Test plan
crates/signature/benches/parallel_scaling.rsand run it inside thersync-profilepodman container withtaskset -c 0-15.perf stat -e cycles,instructions,cache-misses,LLC-loads,LLC-load-missesper thread count for Md5 and Xxh3.MAX_SIGNATURE_THREADS/PARALLEL_SIGNATURE_THRESHOLDaccordingly.