RFR: 8335358: [premain] Explore alternative ways to trigger the end of training run [v5]

[Ioi Lam]

On Mon, 16 Sep 2024 22:18:30 GMT, Mat Carter <macarte at openjdk.org> wrote:

>> AOT training can be ended using either
>> 
>> - -XX: AOTEndTrainingOnMethodEntry =Hello.someMethod [same syntax as CompileOnly]
>> - -XX: AOTEndTrainingOnMethodEntry =Hello.someMethod,Hello.someOtherMethod,count=42
>> - jcmd <pid> AOT.end_training
>> 
>> supports arm64 and x64
>> 
>> note: the AOTEndTrainingOnMethodEntry is ignored when CDSPreImage is specified; this is needed as the phase2 forked java process is passed all phase1 flags along with the -XX:CDSPreImage, but we don't want to run the trigger code in this phase (there may be a better way to handle this state or simply remove the flag from the forked process)
>> 
>> JBS Issue: https://bugs.openjdk.org/browse/JDK-8335358
>
> Mat Carter has updated the pull request incrementally with one additional commit since the last revision:
> 
>   removed extra space left over from reverted change

src/hotspot/cpu/aarch64/templateInterpreterGenerator_aarch64.cpp line 1280:

> 1278:   // AOT training run support
> 1279:   __ end_training_check();
> 1280: 

I wonder how much this will slow down the interpreter, as we trap into the VM on every interpreter entry. Could you do something like


long start = System.currentTimeMillis();
for (int i = 0; i < 10000000; i++) {
    emptyMethod();
}
System.out.println(System.currentMillis() - start();


and run it with something like this? 


rm foo.cds
java -Xint  -XX:+UnlockDiagnosticVMOptions -XX:+CDSManualFinalImage -XX:CacheDataStore=foo.cds ...

src/hotspot/share/opto/parse1.cpp line 1215:

> 1213:   }
> 1214: 
> 1215:   if (CDSConfig::is_dumping_preimage_static_archive_with_triggers() && method()->is_end_training_trigger()) {

Do we come here also if `method()` is being inlined by C2?

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PR Review Comment: https://git.openjdk.org/leyden/pull/21#discussion_r1762265518
PR Review Comment: https://git.openjdk.org/leyden/pull/21#discussion_r1762269791