[jdk11u] Backport the fix of JDK-8180450 to JDK 11?

[Lindenmaier, Goetz]

Hi,

This is a big improvement of performance for subtype checking.
But it is also a big change in central parts of the JVM.
Also, the performance issue solved here is not a regression in
17 (or 11).

So I think while we could consider this for the latest LTE, 21,
we should not bring this to 17 or older releases.  It's just too
risky for these.
Even for 21 it would be a considerable effort to backport it
along with the needed follow-up issues.

> I'm not sure. Looking at the rules for backporting, any bug fix "which
> contributes to the stability, security or performance of the affected line should
> be considered." So this definitely fits in the rule of what is allowed in 11u, but
> of course that doesn't mean that it will be backported, merely that it will be
> considered.
Anyways, in 11 it says "Please note that these common rules do not allow
enhancements to be back-ported, only fixes to bugs."
https://wiki.openjdk.org/display/JDKUpdates/JDK11u
and I would rather categorize it as an enhancement than a bug, although
it's filed as bug in JBS.

Best regards, Goetz.

> -----Original Message-----
> From: jdk-updates-dev <jdk-updates-dev-retn at openjdk.org> On Behalf Of
> Andrew Haley
> Sent: Saturday, October 12, 2024 4:02 PM
> To: jdk-updates-dev at openjdk.org
> Subject: Re: [jdk11u] Backport the fix of JDK-8180450 to JDK 11?
>
> On 10/12/24 10:27, Ziyi Lin wrote:
>
>  > It seems Spark and other concurrent applications will gain significant
> performance improvement from the fix.
>
> I'm not sure. Looking at the rules for backporting, any bug fix "which
> contributes to the stability, security or performance of the affected line should
> be considered." So this definitely fits in the rule of what is allowed in 11u, but
> of course that doesn't mean that it will be backported, merely that it will be
> considered.
>
> As of today, this fix is only available in JDK 23. I do intend to backport it to JDK
> 21 soon, and would welcome help backporting it to 17.
>
>  > Is there a plan to backport the fix to JDK 11 in the future?
>
> There is no strong technical reason why some version of the fix would not
> work on 11u, but it will require work. It's a complicated fix that touches many
> files, in effect rewriting interface type checking in C2, the server compiler.
>
> Given the age of JDK 11, it's questionable whether backporting this will be
> wise. As JDK releases age, they become brittle to change, and breakage
> becomes more likely.
>
> I confess I'm a bit baffled by the Apache discussion at
> https://lists.ap/
> ache.org%2Fthread%2Fptbg70k3tfq4ljz4rbz0y5hqlvof8y31&data=05%7C02%7
> Cgoetz.lindenmaier%40sap.com%7Cb696ddaf0dac44367ee208dceac689d8%7
> C42f7676cf455423c82f6dc2d99791af7%7C0%7C0%7C638643385660128726%
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> UYUWc%2BdipQgzNL5oiKTZ56sRm2oso%3D&reserved=0 . They seem to be
> saying that "Targeting Java >11 excludes Java 11 users" but I don't understand
> why that should be. Can't they build on JDK 11 and also run on 17?
>
> Maybe we should open a conversation with Apache Spark.
>
> --
> Andrew Haley  (he/him)
> Java Platform Lead Engineer
> Red Hat UK Ltd.
> <https://www/.
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