[JFR incubator] [RFR] JDK-8238590: Enable JFR by default during compilation in 8u

[Mario Torre]

Il giorno ven 14 feb 2020 alle ore 18:16 Andrew John Hughes
<gnu.andrew at redhat.com> ha scritto:

> As to enabling by default, I would suggest that we delay this until the
> October cycle, so we have one cycle with the code present, but manually
> enabled, and then spend the 8u272 cycle explicitly testing the effects
> of default enablement. I think having it on by default is the right
> path, but there's no need to rush it.

Yes, I agree and this was my original idea, but during the Committers
workshop was specifically asked to enable it by default right away.
Nonetheless, I don't mind either way :)

I can skip this change if so agreed.

Btw, I'm not sure I understand what's the difference between a merge
and a plain hg import of all those patches exported from
jdk-incubator, history and everything are still preserved since they
are part of the bug id anyway and are in this mailing list, no?

Also, we never update the jfr-incubator exactly in order to apply the
patches on top of the target version and rework if/what is necessary,
I think this is a better strategy but I understand maintainers may
have different preferences here; finally, I agree those patches should
have been (and indeed were!!) reviewed during the last year, and they
are also used in production by Azul and Alibaba, but still given the
scope of the change an extra pair of eyes is welcomed, so while a full
review isn't necessary, I hope to have feedback (by you, Andrew
Dinn/Haley and whoever else has experience and knowledge of hotspot
code), especially on the subtleties of some of this code, and even
more so on the performance aspect, which is the one feedback we lack
the most since, as you noted, not many have been playing with the
incubator thus far.

Cheers,
Mario
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