RFR: 8370947: Mitigate Neoverse-N1 erratum 1542419 negative impact on GenZGC performance

[Evgeny Astigeevich]

On Thu, 20 Nov 2025 15:27:37 GMT, Axel Boldt-Christmas <aboldtch at openjdk.org> wrote:

> Is this only because of the Neoverse-N1 workaround?

Yes, it is.

> If that is the case we could reach this point if NeoverseN1Errata1542419 is either set by the user or mislabeled on some CPU without this workaround.

We only set NeoverseN1Errata1542419 to true if CPU is Neoverse N1 with the errata and it is not set by an user. We rely on Linux kernel cpuinfo correctly providing us information about Neoverse N1 revision. I think it's worth to check explicitly all affected revisions. This will mitigate Linux kernels not correctly setting revisions.
We can issue a warning if an user sets it to true and CPU is not Neoverse N1 with the errata.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/28328#discussion_r2546769534