[jdk21u-dev] Withdrawn: 8334890: Missing unconditional cross modifying fence in nmethod entry barriers

[duke]

On Thu, 7 Nov 2024 02:18:54 GMT, Boris Ulasevich <bulasevich at openjdk.org> wrote:

> The change adds an unconditional memory barrier to guarantee the instruction fetcher observes the correct updated immediate.
> 
> Merge conflict caused by minor context difference (added comment in a mainline): fixed manually.
> 
> Testing: jtreg tier 1-3 on arm64 and x64.
> 
> **Update.** The backport is controversial: while the functional change is correct and necessary, it introduces a regression in SPECjvm2008: [JDK-8337778](https://bugs.openjdk.org/browse/JDK-8337778)
> 
> **Update.**
> - https://bugs.openjdk.org/browse/JDK-8337778 is closed with Won't Fix resultion
> 
> SPECjvm2008-Derby-ZGC performance on linux-aarch64 is not affected with patch applied to jdk21u
> - before:
>   - Score on derby: 5375.49 ops/m
>   - Score on derby: 5430.11 ops/m
>   - Score on derby: 5413.50 ops/m
>   - Score on derby: 5363.00 ops/m
>   - Score on derby: 5359.83 ops/m
>   - Score on derby: 5325.92 ops/m
>   - Score on derby: 5464.94 ops/m
>   - Score on derby: 5413.74 ops/m
> - after:
>   - Score on derby: 5476.12 ops/m
>   - Score on derby: 5280.42 ops/m
>   - Score on derby: 5446.40 ops/m
>   - Score on derby: 5402.60 ops/m
>   - Score on derby: 5470.78 ops/m
>   - Score on derby: 5409.36 ops/m
>   - Score on derby: 5403.56 ops/m
>   - Score on derby: 5457.11 ops/m

This pull request has been closed without being integrated.

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PR: https://git.openjdk.org/jdk21u-dev/pull/1131