Withdrawn: 8275728: Add simple Producer/Consumer microbenchmark for Thread.onSpinWait

[Evgeny Astigeevich]

On Wed, 10 Nov 2021 18:07:47 GMT, Evgeny Astigeevich <duke at openjdk.java.net> wrote:

> This is a microbenchmarks to demonstrate `Thread.onSpinWait` can be used to avoid heavy locks.
> The microbenchmark differs from [Gil's original benchmark](https://github.com/giltene/GilExamples/tree/master/SpinWaitTest) and [Dmitry's variations](http://cr.openjdk.java.net/~dchuyko/8186670/yield/spinwait.html). Those benchmarks produce/consume data by incrementing a volatile counter. The latency of such operations is almost zero. They also don't use heavy locks. According to [Gil's SpinWaitTest.java](https://github.com/giltene/GilExamples/blob/master/SpinWaitTest/src/main/java/SpinWaitTest.java):
>> This test can be used to measure and document the impact of Runtime.onSpinWait() behavior
>>  on thread-to-thread communication latencies. E.g. when the two threads are pinned to
>> the two hardware threads of a shared x86 core (with a shared L1), this test will
>> demonstrate an estimate the best case thread-to-thread latencies possible on the
>> platform
> 
> Gil's microbenchmark targets SMT cases (x86 hyperthreading). As not all CPUs support SMT, the microbenchmarks cannot demonstrate benefits of `Thread.onSpinWait`. It is actually opposite. They show `Thread.onSpinWait`  has negative impact on performance.
> 
> The microbenchmark from PR uses `BigInteger` to have 100 - 200 ns latencies for producing/consuming data. These latencies can cause either a producer or a consumer to wait each another. Waiting is implemented with `Object.wait`/`Object.notify` which are heavy. `Thread.onSpinWait` can be used in a spin loop to avoid them.
> 
> **ARM64 results**:
> - No spin loop
> 
> Benchmark                               (maxNum)  (spinNum)  Mode  Cnt     Score    Error  Units
> ThreadOnSpinWaitProducerConsumer.trial       100          0  avgt   75  1520.448 ± 40.507  us/op
> 
> - No `Thread.onSpinWait` intrinsic
> 
> Benchmark                               (maxNum)  (spinNum)  Mode  Cnt     Score    Error  Units
> ThreadOnSpinWaitProducerConsumer.trial       100        125  avgt   75  1580.756 ± 47.501  us/op
> 
> - `ISB`-based `Thread.onSpinWait` intrinsic
> 
> Benchmark                               (maxNum)  (spinNum)  Mode  Cnt    Score     Error  Units
> ThreadOnSpinWaitProducerConsumer.trial       100        125  avgt   75  617.454 ± 174.431  us/op
> 
> 
> **X86_64 results**:
> - No spin loop
> 
> Benchmark                               (maxNum)  (spinNum)  Mode  Cnt    Score     Error  Units
> ThreadOnSpinWaitProducerConsumer.trial      100        125  avgt   75  1417.944 ± 1.691  us/op
> 
> - No `Thread.onSpinWait` intrinsic
> 
> Benchmark                               (maxNum)  (spinNum)  Mode  Cnt    Score     Error  Units
> ThreadOnSpinWaitProducerConsumer.trial      100        125  avgt   75  1410.987 ± 2.093  us/op
> 
> - `PAUSE`-based `Thread.onSpinWait` intrinsic
> 
> Benchmark                               (maxNum)  (spinNum)  Mode  Cnt    Score     Error  Units
> ThreadOnSpinWaitProducerConsumer.trial      100        125  avgt   75  217.054 ± 1.283  us/op

This pull request has been closed without being integrated.

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PR: https://git.openjdk.java.net/jdk/pull/6338