Feasibility to backport new allocation event and event throttling to JDK 8,11

[Mukilesh Sethu]

Hi Erik,

Thanks for the reply.

It makes sense to wait till it has been thoroughly stress tested. But do we
need to wait 6 months after JDK 16 has been released ? How about disabling
it by default in older versions ? Maybe a light version of object
allocation sample event ?

>Those who really want allocation sampling in an old release can turn on
the TLAB events. There will be perhaps 1% additional overhead (YMMV), but
that price is only paid by those who really want the feature.

Yeah, we have seen overhead quite higher than 1% :) To my knowledge, there
was one optimization made to improve it (
https://mail.openjdk.java.net/pipermail/hotspot-jfr-dev/2020-July/001605.html)
but it wasn't good enough. (Please let me know if I have missed any further
optimizations).

Thanks,
Mukilesh

On Wed, Dec 16, 2020 at 1:44 PM Erik Gahlin <erik.gahlin at oracle.com> wrote:

> Hi Mukilesh,
>
> The Object Allocation Sample event is completely new and before
> considering a backport, it should be thoroughly stress tested. If it turns
> out to be issues, we may have to pull it out of JDK 16, or at least disable
> the event by default.
>
> Then we should probably wait 6 months after JDK 16 has been released, so
> we can make adjustments to the configuration or sampling mechanism, after
> feedback from users. Then it can be decided, if it should be backported.
>
> In my opinion, it shouldn’t. Having different type of events in different
> update releases, or distributions, creates confusion. Users don’t want
> things to fail due to a security upgrade. Those who really want allocation
> sampling in an old release can turn on the TLAB events. There will be
> perhaps 1% additional overhead (YMMV), but that price is only paid by those
> who really want the feature.
>
> Everybody else can enjoy the stability.
>
> Thanks
> Erik
>
> On 11 Dec 2020, at 23:52, Mukilesh Sethu <mukilesh.sethu at gmail.com> wrote:
>
> Hey,
>
> I could see new allocation event and event throttling was added recently(
> https://github.com/openjdk/jdk/pull/1624). I was wondering if we could
> backport these changes to JDK 8,11. I am just checking if there are any
> concerns in backporting these changes to JDK 8,11 as it introduces new
> event and new event functionality (throttling). From the initial look I
> think backport should be trivial, please let me know what you think ?
>
> Thanks,
> Mukilesh
>
>
>