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bytes: degradations in compareBytes benchmarks between 1.7 and 1.8 #18986

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laboger opened this issue Feb 7, 2017 · 2 comments
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bytes: degradations in compareBytes benchmarks between 1.7 and 1.8 #18986

laboger opened this issue Feb 7, 2017 · 2 comments
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@laboger
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laboger commented Feb 7, 2017

There are two benchmarks in the bytes test for IndexByte that degraded between 1.7 and 1.8 and possibly should be investigated.

BenchmarkCompareBytesIdentical-16 6.91 11.4 +64.98%
BenchmarkCompareBytesToNil-16 7.40 11.1 +50.00%

And this one! I think it is crossing a page boundary or something.
BenchmarkCompareBytesBigIdentical-16 6.62 46511 +702483.08%
@laboger laboger closed this as completed Feb 7, 2017
@bradfitz
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bradfitz commented Feb 7, 2017

Did you mean to close this? Which OS/arch?

@mundaym
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mundaym commented Feb 8, 2017

Not sure about the others but the BenchmarkCompareBytesBigIdentical numbers indicate that the bytes.Compare function is missing a check for matching pointers. In other words it is probably missing a special case for this situation:

a := [65536]byte{}
bytes.Compare(a[:], a[:])

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@bradfitz @gopherbot @laboger @mundaym