ARROW-10058: [C++] Improve repeated levels conversion without BMI2

[pitrou]

Use a lookup table to emulate PEXT 5 bits at a time.
Remove the slow scalar path.

[pitrou]

See JIRA issue for benchmarks. Would be nice to have benchmarks on other machines. @emkornfield

[pitrou]

I also notice that we call internal::GreaterThanBitmap for each 64 levels, which always goes through the dynamic dispatch indirection (meaning two function calls, I think). We could call GreaterThanBitmapImpl but that requires compiling a specialized version of level_conversion_inc.h for AVX2, otherwise we lose performance.

[github-actions]

https://issues.apache.org/jira/browse/ARROW-10058

[emkornfield]

@pitrou I'm devoting most of my bandwidth to try to finish up the parquet read component this week, is it ok if I take a closer look next week (hopefully with enough time before an RC is cut?)

[emkornfield]

I also notice that we call internal::GreaterThanBitmap for each 64 levels, which always goes through the dynamic dispatch indirection (meaning two function calls, I think). We could call GreaterThanBitmapImpl but that requires compiling a specialized version of level_conversion_inc.h for AVX2, otherwise we lose performance.

yeah it isn't ideal, it is possible there is a better factoring in there but it seemed hard to do and isolate BMI2 special instructions, I guess if this isn't too much slower then BMI2 on intel we could potentially collapse everything, but I would not expect that to be the case.

[pitrou]

is it ok if I take a closer look next week

No problem.

but I would not expect that to be the case.

Right. The emulation is probably much slower.

[pitrou]

Updated benchmarks on AMD Ryzen:

                         benchmark         baseline         contender  change %                                                                                                                                           counters
0     BM_ReadListOfStructColumn/50  392.881 MiB/sec   564.029 MiB/sec    43.562     {'run_name': 'BM_ReadListOfStructColumn/50', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 23}
10            BM_ReadListColumn/50  485.560 MiB/sec   675.023 MiB/sec    39.019             {'run_name': 'BM_ReadListColumn/50', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 42}
7     BM_ReadStructOfListColumn/50  341.782 MiB/sec   462.097 MiB/sec    35.202     {'run_name': 'BM_ReadStructOfListColumn/50', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 20}
3       BM_ReadListOfListColumn/50  447.657 MiB/sec   566.594 MiB/sec    26.569       {'run_name': 'BM_ReadListOfListColumn/50', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 39}
23            BM_ReadListColumn/99    1.168 GiB/sec     1.365 GiB/sec    16.883            {'run_name': 'BM_ReadListColumn/99', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 102}
4     BM_ReadListOfStructColumn/99  975.429 MiB/sec     1.095 GiB/sec    14.925     {'run_name': 'BM_ReadListOfStructColumn/99', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 56}
9     BM_ReadStructOfListColumn/99  798.058 MiB/sec   896.789 MiB/sec    12.371     {'run_name': 'BM_ReadStructOfListColumn/99', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 46}
22      BM_ReadListOfListColumn/99    1.050 GiB/sec     1.168 GiB/sec    11.159       {'run_name': 'BM_ReadListOfListColumn/99', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 94}
1      BM_ReadListOfStructColumn/1  654.576 MiB/sec   725.676 MiB/sec    10.862      {'run_name': 'BM_ReadListOfStructColumn/1', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 38}
19             BM_ReadListColumn/1  919.949 MiB/sec  1005.740 MiB/sec     9.326              {'run_name': 'BM_ReadListColumn/1', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 81}
11     BM_ReadListOfStructColumn/0  835.259 MiB/sec   908.920 MiB/sec     8.819      {'run_name': 'BM_ReadListOfStructColumn/0', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 49}
17     BM_ReadStructOfListColumn/1  605.129 MiB/sec   649.556 MiB/sec     7.342      {'run_name': 'BM_ReadStructOfListColumn/1', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 35}
8              BM_ReadListColumn/0    1.067 GiB/sec     1.145 GiB/sec     7.334              {'run_name': 'BM_ReadListColumn/0', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 92}
5      BM_ReadStructOfListColumn/0  700.157 MiB/sec   740.414 MiB/sec     5.750      {'run_name': 'BM_ReadStructOfListColumn/0', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 41}
6        BM_ReadListOfListColumn/0  929.109 MiB/sec   966.896 MiB/sec     4.067        {'run_name': 'BM_ReadListOfListColumn/0', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 82}
14  BM_ReadStructOfStructColumn/50    1.537 GiB/sec     1.595 GiB/sec     3.772   {'run_name': 'BM_ReadStructOfStructColumn/50', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 45}
13          BM_ReadStructColumn/99    4.211 GiB/sec     4.330 GiB/sec     2.835          {'run_name': 'BM_ReadStructColumn/99', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 252}
20          BM_ReadStructColumn/50    1.155 GiB/sec     1.187 GiB/sec     2.755           {'run_name': 'BM_ReadStructColumn/50', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 69}
15   BM_ReadStructOfStructColumn/1    1.802 GiB/sec     1.849 GiB/sec     2.566    {'run_name': 'BM_ReadStructOfStructColumn/1', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 53}
12           BM_ReadStructColumn/1    1.798 GiB/sec     1.843 GiB/sec     2.521           {'run_name': 'BM_ReadStructColumn/1', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 110}
2   BM_ReadStructOfStructColumn/99    3.464 GiB/sec     3.530 GiB/sec     1.898  {'run_name': 'BM_ReadStructOfStructColumn/99', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 100}
16   BM_ReadStructOfStructColumn/0    6.021 GiB/sec     6.065 GiB/sec     0.724   {'run_name': 'BM_ReadStructOfStructColumn/0', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 179}
21           BM_ReadStructColumn/0    6.821 GiB/sec     6.812 GiB/sec    -0.137           {'run_name': 'BM_ReadStructColumn/0', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 410}
18       BM_ReadListOfListColumn/1  805.644 MiB/sec   801.480 MiB/sec    -0.517        {'run_name': 'BM_ReadListOfListColumn/1', 'run_type': 'iteration', 'repetitions': 0, 'repetition_index': 0, 'threads': 1, 'iterations': 70}

[emkornfield]

sorry some personal issues came up. hope to have time tonight to review this and other parquet related CLs

[pitrou]

For the record, if I profile BM_ReadStructOfListColumn/50, I get the following hot spots (in cycles spent):

• ~19% in DefRepLevelsToListInfo
• ~15% in DelimitRecords
• ~11% in BitRunReader::NextRun
• ~10% in SpacedExpand
• ~6% in DictionaryConverter<int>::Copy
• ~5% in PathWriteContext::AppendRepLevels

And ExtractBitsSoftware (the PEXT emulation) only takes ~1.1%, which seems good enough for now.

[emkornfield]

+1. Thanks.