RFR: 8350209: Preserve adapters in AOT cache [v10]

[Ashutosh Mehra]

On Tue, 29 Apr 2025 06:27:41 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 with a new target base due to a merge or a rebase. The pull request now contains 11 commits:
> 
>  - Fix C strings caching
>  - Merge branch 'master' into JDK-8350209
>  - Merge branch 'master' into JDK-8350209
>  - Downgraded UL as asked. Added synchronization to C strings caching.
>  - Fix message
>  - Generate far jumps for AOT code on AArch64
>  - remove _enabled suffix
>  - Add sanity test for AOTAdapterCaching flag
>  - AOT code flags are ignored when AOTCache is not specified. Set range for AOTCodeMaxSize values.
>  - Removed unused AOTCodeSection class
>  - ... and 1 more: https://git.openjdk.org/jdk/compare/7cf190fb...1b0c89f6

Just to note there is still some code related to blobs but we are not storing them yet in the aot code cache. But I think we would need them pretty soon. So I think it should be okay to keep that code as is.

rest lgtm

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PR Comment: https://git.openjdk.org/jdk/pull/24740#issuecomment-2839210239
PR Comment: https://git.openjdk.org/jdk/pull/24740#issuecomment-2839211140