Integrated: 8320239: add dynamic switch for JvmtiVTMSTransitionDisabler sync protocol

[Serguei Spitsyn]

On Thu, 16 Nov 2023 12:35:08 GMT, Serguei Spitsyn <sspitsyn at openjdk.org> wrote:

> This is an update for a performance/scalability enhancement.
> 
> The `JvmtiVTMSTransitionDisabler`sync protocol is on a performance critical path of the virtual threads mount state transitions (VTMS transitions). It has a noticeable performance overhead (about 10%) which contributes to the combined JVMTI performance overhead when Java apps are executed with loaded JVMTI agents.
> 
> Please, also see another/related performance issue which contributes around 70% of total performance overhead:
> [8308614](https://bugs.openjdk.org/browse/JDK-8308614): Enabling JVMTI ClassLoad event slows down vthread creation by factor 10
> 
> Testing:
>  - Ran mach5 tiers 1-6 with no regressions noticed.

This pull request has now been integrated.

Changeset: 41daa3b9
Author:    Serguei Spitsyn <sspitsyn at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/41daa3b934255420dcf414cf9045289ba05a9f48
Stats:     47 lines in 2 files changed: 40 ins; 4 del; 3 mod

8320239: add dynamic switch for JvmtiVTMSTransitionDisabler sync protocol

Reviewed-by: lmesnik, pchilanomate, amenkov

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PR: https://git.openjdk.org/jdk/pull/16688