RFR: 8350209: Preserve adapters in AOT cache [v8]

[Vladimir Kozlov]

On Sun, 27 Apr 2025 21:52:43 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> [JEP 483](https://bugs.openjdk.org/browse/JDK-8315737) preserves class information in AOT cache which helps Java startup performance.
>> 
>> We should also preserve adapters (i2c, c2i) to further improve performance of class linking where adapters are generated.
>> 
>> Short running Java application can see several percents improvement. I got 6% improvement when ran `HelloWorld.java` on Linux-x64 Ice Lake CPU (2.5Ghz):
>> 
>> 
>> (perf stat -r 100 java -XX:AOTCache=app.aotcache -cp hello.jar HelloWorld > /dev/null) 2>&1 | grep elapsed
>>          0.0299401 +- 0.0000504 seconds time elapsed  ( +-  0.17% )
>> 
>> (perf stat -r 100 java -XX:AOTCache=app.aotcache -XX:+UnlockDiagnosticVMOptions -XX:-AOTAdapterCaching -cp hello.jar HelloWorld > /dev/null) 2>&1 | grep elapsed
>>          0.0318654 +- 0.0000535 seconds time elapsed  ( +-  0.17% )
>> 
>> 
>> New diagnostic flags are introduced (use `-XX:+UnlockDiagnosticVMOptions` to unlock them):
>> 
>> 
>> -XX:+AOTAdapterCaching  - Enable or disable saving and restoring i2c2i adapters
>> -XX:AOTCodeMaxSize=10*M - buffer size in bytes for AOT code caching
>> -XX:+AbortVMOnAOTCodeFailure - Abort VM on the first occurrence of AOT code caching failure
>> 
>> By default `AOTAdapterCaching` is `false` and enabled ergonomically when `-XX:AOTCache` is specified.
>> This flag is ignored when `AOTCache` is not specified.
>> 
>> To use AOT adapters follow process described in JEP 483:
>> 
>> 
>> java -XX:AOTMode=record -XX:AOTConfiguration=app.aotconf -cp app.jar App
>> java -XX:AOTMode=create -XX:AOTConfiguration=app.aotconf -XX:AOTCache=app.aot -cp app.jar
>> java -XX:AOTCache=app.aot -cp app.jar App
>> 
>> 
>> There are several new UL flag combinations to trace the AOT code caching process:
>> 
>> 
>> -Xlog:aot+codecache+init -Xlog:aot+codecache+exit -Xlog:aot+codecache+stubs
>> 
>> 
>> @ashu-mehra is main author of changes. He implemented adapters caching.
>> I did main framework (`AOTCodeCache` class) for saving and loading AOT code.
>> 
>> Tested tier1-6,10, which includes tests with `AOTClassLinking` enabled. Also Xcomp,stress and JCK.
>
> Vladimir Kozlov has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Downgraded UL as asked. Added synchronization to C strings caching.

I repeated testing again - it passed.

@iwanowww, @ashu-mehra please review again.

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PR Comment: https://git.openjdk.org/jdk/pull/24740#issuecomment-2833656967