On Wed, 10 Nov 2021 18:07:47 GMT, Evgeny Astigeevich <d...@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. ------------- PR: https://git.openjdk.java.net/jdk/pull/6338
