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ARROW-8793: [C++] Do not inline BitUtil::SetBitsTo #7296

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ARROW-8793: [C++] Do not inline BitUtil::SetBitsTo #7296

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@wesm wesm commented May 27, 2020 •
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Local benchmarks suggest that there is 3-4 ns of overhead for manipulating small bitmaps when it is not inline.

inline (argument is byte size of bitmap):

--------------------------------------------------------
Benchmark                 Time           CPU Iterations
--------------------------------------------------------
SetBitsTo/2               3 ns          3 ns  271439203   733.294MB/s
SetBitsTo/16              2 ns          2 ns  308813758   6.49485GB/s
SetBitsTo/1024            9 ns          9 ns   79821710   109.078GB/s
SetBitsTo/131072       2029 ns       2029 ns     325563   60.1566GB/s

non-inline:

--------------------------------------------------------
Benchmark                 Time           CPU Iterations
--------------------------------------------------------
SetBitsTo/2               6 ns          6 ns  129335891    334.62MB/s
SetBitsTo/16              6 ns          6 ns  122741527   2.53134GB/s
SetBitsTo/1024           11 ns         11 ns   64547137   87.1395GB/s
SetBitsTo/131072       2010 ns       2010 ns     332558   60.7215GB/s

If it can be demonstrated that inlining can meaningfully improve the macroperformance of some function, then we could lift the implementation into a SetBitsToInline, but until then I think it makes sense to keep it in bit_util.cc

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https://issues.apache.org/jira/browse/ARROW-8793

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wesm commented May 28, 2020

+1

@wesm wesm closed this in e5a0893 May 28, 2020
@wesm wesm deleted the ARROW-8793 branch May 28, 2020 13:26
@asfimport asfimport mentioned this pull request May 28, 2020
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