[11u] RFR(S): 8241234: Unify monitor enter/exit runtime entries.

[Severin Gehwolf]

On Thu, 2020-08-27 at 16:25 +0100, Andrew Haley wrote:
> Hi,
> 
> On 27/08/2020 11:04, Doerr, Martin wrote:
> > > Why is anyone backporting a P4 Enhancement? Seems weird.
> > This is a good question in general. Personally, I'd vote for
> > backporting fewer less important things to 11u in the future. We
> > should better focus on 17 IMHO.
> > 
> > However, there are some arguments for backporting this one:
> > - Oracle has done so. There may be more backports in this area and
> > I'd expect less effort if we have the same code in the open version.
> > - Performance is supposed to be better. (Though I didn't measure it.)
> > - New code is much cleaner. Let's keep in mind that we have to
> > support it for quite a while.
> > 
> > Are you ok with it?
> 
> I'm unsure. While "Oracle has backported it" has been a slam-dunk
> justification for many patches, I am concerned about the destabilizing
> effect of the volume of patches we are processing.
> 
> "Better performance" is not in itself justification for a backport
> unless the improvement is really compelling.
> 
> "Cleanups" are a red flag. The miserable history of code that has been
> broken by seemingly innocuous cleanups is long. This is a big change
> that affects some very delicate code, but the fact that there is
> already a GraalVM patch we can use is quite persuasive.
> 
> So I'm not refusing it, I want people's opinions.

It seems like a nice-to-have fix for OpenJDK 11 itself. Interest seems
to be coming from Graal. Until there is a more compelling reason to
backport this (other than performance for some JVMCI impl) we shouldn't
backport this. We already have a label for these: jdk11u-jvmci-defer.
We should apply that and re-evaluate later if needed.

My $0.02

Thanks,
Severin