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f05ddf0967
" The LSA small objects allocation latency is greatly affected by the way this allocator encodes the object descriptor in front of each allocated slot. Nowadays it's one of VLE variants implemented with the help of a loop. Re-implementing this piece with less instructions and without a loop allows greatly reducing the allocation latency. The speed-up mostly comes from loop-less code that doesn't confuse branch predictor. Also the express encoder seems to benefit from writing 8 bytes of the encoded value in one go, rather than byte- -by-byte. Perf measurements: 1. (new) logallog test shows ~40% smaller times 2. perf_mutation in release mode shows ~2% increase in tps 3. the encoder itself is 2 - 4 times faster on x86_64 and 1.05 - 3 times faster on aarch64. The speed-up depends on the 'encoded length', old encoder has linear time, the new one is constant tests: unit(dev), perf(release), just encoder on Aarch64 " * 'br-lsa-alloc-latency-4' of https://github.com/xemul/scylla: lsa: Use express encoder uleb64: Add express encoding lsa: Extract uleb64 code into header test: LSA allocation perf test