Virtual thread overhead in SharedRuntime::handle_wrong_method

[Francesco Nigro]

FYI I have have already share some of these things with some loom dev at
https://github.com/async-profiler/async-profiler/issues/779

Il lun 21 ago 2023, 12:00 Gillespie, Oli <ogillesp at amazon.co.uk> ha scritto:

> Hi,
>
> I've been using virtual threads and I noticed some apparently significant
> overhead in SharedRuntime::handle_wrong_method.
>
> A simple 'benchmark'/stress test profiled with async-profiler shows (among
> other similar stacks):
>
> ```
> --- 29055613704 ns (21.14%), 288804 samples
>   [ 0] ImmutableOopMap::update_register_map(frame const*, RegisterMap*)
> const
>   [ 1] vframeStream::vframeStream(JavaThread*, bool, bool, bool)
>   [ 2] SharedRuntime::find_callee_method(JavaThread*)
>   [ 3] SharedRuntime::reresolve_call_site(JavaThread*)
>   [ 4] SharedRuntime::handle_wrong_method(JavaThread*)
>   [ 5] jdk.internal.vm.Continuation.enterSpecial
>   [ 6] jdk.internal.vm.Continuation.run
>   [ 7] java.lang.VirtualThread.runContinuation
>   [ 8] java.lang.VirtualThread$$Lambda.0x00007ffad006e3d8.run
>   [ 9] java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec
>   [10] java.util.concurrent.ForkJoinTask.doExec
>   [11] java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec
>   [12] java.util.concurrent.ForkJoinPool.scan
>   [13] java.util.concurrent.ForkJoinPool.runWorker
>   [14] java.util.concurrent.ForkJoinWorkerThread.run
> ```
>
> Is this just the expected path+cost of swapping between virtual threads,
> or is there something surprising happening here?
>
> My code for the test is:
>
> ```
> import java.util.concurrent.*;
>
> public class Virt {
>     public static void main(String[] args) throws Exception {
>         while (true) {
>             ExecutorService e =
> Executors.newVirtualThreadPerTaskExecutor();
>             for (int i = 0; i < 100_000; i++) e.submit(Main::task);
>             e.shutdown(); e.awaitTermination(100, TimeUnit.MINUTES);
>         }
>     }
>     static void task() { }
> }
> ```
>
> Notes:
> - I'm running with JDK21, using `java -XX:+UnlockExperimentalVMOptions
> -XX:-DoJVMTIVirtualThreadTransitions Virt.java` since I know async-profiler
> as a JVMTI agent triggers some other overheads which would be distracting
> in the profiling data.
> - Another user saw similar behaviour in
> https://github.com/async-profiler/async-profiler/issues/779#issuecomment-1651225252
> .
>
> Apologies if this is just totally expected behaviour, but I couldn't find
> any discussion on it.
>
> Regards,
>
> Oli
>
>
>
> Amazon Development Centre (London) Ltd. Registered in England and Wales
> with registration number 04543232 with its registered office at 1 Principal
> Place, Worship Street, London EC2A 2FA, United Kingdom.
>
>
>
>
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