RFR: JDK-8289524: Add JFR JIT restart event [v3]

[Markus Grönlund]

On Thu, 14 Jul 2022 14:26:01 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

>> The JIT compiler restarts (see restart_compiler in NMethodSweeper::sweep_code_cache) would be a helpful addition to the JFR events. Currently we log the JIT stop operations in JFR (EventCodeCacheFull) but no restart.
>
> Matthias Baesken has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Bring back JitRestart event, add codeCacheMaxCapacity

Changes requested by mgronlun (Reviewer).

src/hotspot/share/jfr/metadata/metadata.xml line 563:

> 561:   <Event name="JitRestart" category="Java Virtual Machine, Compiler" label="JIT restart" stackTrace="false" startTime="false" thread="true">
> 562:     <Field type="int" name="freedMemory" label="Freed Memory" />
> 563:     <Field type="ulong" name="codeCacheMaxCapacity" label="CodeCache maximum capacity" />

Is codeCacheMaxCapacity the current in-use size of the CodeCache, in bytes? It should have the contentType="bytes" in that case. Also "freedMemory" should have the same contentType.

src/hotspot/share/jfr/metadata/metadata.xml line 620:

> 618:     <Field type="ulong" contentType="bytes" name="unallocatedCapacity" label="Unallocated" />
> 619:     <Field type="int" name="fullCount" label="Full Count" />
> 620:     <Field type="ulong" name="codeCacheMaxCapacity" label="CodeCache maximum capacity" />

contentType="bytes"

test/jdk/jdk/jfr/event/metadata/TestLookForUntestedEvents.java line 57:

> 55:     private static final Set<String> hardToTestEvents = new HashSet<>(
> 56:         Arrays.asList(
> 57:             "DataLoss", "IntFlag", "ReservedStackActivation", "JitRestart",

Can we create a test? There is an existing test for CodeCacheFull, maybe derive from it to create a test also for the JitRestart event?

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PR: https://git.openjdk.org/jdk/pull/9334