RFR: 8310843: Reimplement ByteArray and ByteArrayLittleEndian with Unsafe [v10]

[Maurizio Cimadamore]

On Thu, 20 Jul 2023 16:58:44 GMT, Glavo <duke at openjdk.org> wrote:

> By the way, I ran `LoopOverNonConstantHeap` on the 3700x platform, and the performance of ByteBuffer was also poor:

I finally see it.


Benchmark                           (polluteProfile)  Mode  Cnt  Score   Error  Units
LoopOverNonConstantHeap.BB_get                 false  avgt   30  1.801 ± 0.020  ns/op
LoopOverNonConstantHeap.unsafe_get             false  avgt   30  0.567 ± 0.007  


It seems that, between updating JMH and rebuilding the JDK from scratch, *something* did the trick.

While I knew that random access on a BB is slower than Unsafe (as there's an extra check), whereas looped access is as fast (as C2 is good at hoisting the checks outside the loop, as shown in the benchmark). Note also that we are in the nanosecond realm, so each instruction here counts.

Is there any benchmark for DataInput/Output stream that can be used? I mean, it would be interesting to understand how these numbers translate when running the stuff that is built on top.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14636#discussion_r1269763302