[GitHub] [arrow] pitrou commented on pull request #6985: ARROW-8413: [C++][Parquet] Refactor Generating validity bitmap for values column

[GitBox <gi...@apache.org>]

pitrou commented on pull request #6985:
URL: https://github.com/apache/arrow/pull/6985#issuecomment-637533180


   Here are some benchmarks on my machine, with gcc 7.5:
   * `ARROW_SIMD_LEVEL=AVX2`:
   ```
   BM_DefinitionLevelsToBitmapRepeatedAllMissing         934 ns          934 ns      3004804 bytes_per_second=2.04274G/s
   BM_DefinitionLevelsToBitmapRepeatedAllPresent        1327 ns         1327 ns      1908147 bytes_per_second=1.4377G/s
   BM_DefinitionLevelsToBitmapRepeatedMostPresent       1725 ns         1725 ns      1649108 bytes_per_second=1.10569G/s
   ```
   * `ARROW_SIMD_LEVEL=SSE4_2`:
   ```
   BM_DefinitionLevelsToBitmapRepeatedAllMissing        1384 ns         1384 ns      2029778 bytes_per_second=1.37806G/s
   BM_DefinitionLevelsToBitmapRepeatedAllPresent        2054 ns         2053 ns      1247469 bytes_per_second=951.163M/s
   BM_DefinitionLevelsToBitmapRepeatedMostPresent       2124 ns         2124 ns      1303578 bytes_per_second=919.503M/s
   ```
   * `ARROW_SIMD_LEVEL=NONE`:
   ```
   BM_DefinitionLevelsToBitmapRepeatedAllMissing         925 ns          925 ns      3025393 bytes_per_second=2.06245G/s
   BM_DefinitionLevelsToBitmapRepeatedAllPresent        1505 ns         1504 ns      1881938 bytes_per_second=1.26785G/s
   BM_DefinitionLevelsToBitmapRepeatedMostPresent       1725 ns         1725 ns      1598820 bytes_per_second=1.10599G/s
   ```
   
   So it seems that gcc's SSE4.2 auto-vectorization may lead to suboptimal code, but that's not a problem for this PR.


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