Parsing array of varints optimizations #13256
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@palade Thank you for the pull request, but unfortunately I don't think we will be able to accept it at this time. We are not yet set up to use AVX 512 BMI, so we're not in a good position to maintain code that uses it. This might be something we could accept in the future though, especially if we can quantify the performance benefits in production. |
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Actually I heard from @fowles that AVX 512 instructions cause modern CPUs to downclock, so that problem will likely prevent us from ever using these instructions for varint parsing. |
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This PR has the changes for parsing array of varints. Most of the changes originate in the
ReadPackedVarintandReadPackedVarintArrayfunctions. The core of optimizations is to break the one-at-a-time parsing in the original code into a series of steps to leverage SIMD instructions.