RFR: 8268398: 15% increase in JFR footprint in Noop-Base [v2]

[Erik Gahlin]

> Hi,
> 
> Could I have a review of a PR that skips bytecode instrumentation for container events and initialisation of Container.metrics() if the JVM isn't running in a container, or to be precise, if container support is not available. If a user specifies -XX:-UseContainerSupport, events are not emitted. This was the case before this PR, and maybe it should be fixed, but it's an enhancement and outside the scope of this bug.
> 
> Testing:
> - jdk/jdk/jfr
> - Manual testing in a container.
> 
> I tried to run test/hotspot/jtreg/containers/docker/TestJFREvents.java, but the test is broken (image can't be built, so test is skipped). 
> 
> This fix may not be sufficient to reduce footprint introduced by the container events, but [JDK-8282420: JFR: Remove event handlers](https://bugs.openjdk.org/browse/JDK-8282420) also reduced number of loaded classes which should reduce footprint in JDK 19. There are an ongoing enhancement work to generate bytecode and metadata at build time, which will help, but it will be integrated in JDK 20. 
> 
> Thanks
> Erik

Erik Gahlin has updated the pull request incrementally with one additional commit since the last revision:

  Update comment

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

Changes:
  - all: https://git.openjdk.org/jdk19/pull/31/files
  - new: https://git.openjdk.org/jdk19/pull/31/files/ac52ac51..66edea79

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk19&pr=31&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk19&pr=31&range=00-01

  Stats: 2 lines in 2 files changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk19/pull/31.diff
  Fetch: git fetch https://git.openjdk.org/jdk19 pull/31/head:pull/31

PR: https://git.openjdk.org/jdk19/pull/31