RFR: 8203359: Container level resources events

[Severin Gehwolf]

On Mon, 22 Mar 2021 15:57:12 GMT, Jaroslav Bachorik <jbachorik at openjdk.org> wrote:

> With this change it becomes possible to surface various cgroup level metrics (available via `jdk.internal.platform.Metrics`) as JFR events.
> 
> Only a subset of the metrics exposed by `jdk.internal.platform.Metrics` is turned into JFR events to start with.
> * CPU related metrics
> * Memory related metrics
> * I/O related metrics
> 
> For each of those subsystems a configuration data will be emitted as well. The initial proposal is to emit the configuration data events at least once per chunk and the metrics values at 30 seconds interval. 
> By using these values the emitted events seem to contain useful information without increasing overhead (the metrics values are read from `/proc` filesystem so that should not be done too frequently).

@jbachorik Would it make sense for `ContainerConfigurationEvent` to include the underlying cgroup version info (v1 or legacy vs. v2 or unified)? `Metrics.getProvider()` should give that info.

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PR: https://git.openjdk.java.net/jdk/pull/3126