RFR: Prefer to take AOT method from the SC queue faster

[Aleksey Shipilev]

On Fri, 6 Sep 2024 22:23:41 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> Probably WIP. Humor me for a second: why could not / should not we take the AOT task for "compilation" (installation, really) right away like this? I suspect when SC queues are overwhelmed with N elements, we keep walking the entire SC queue for no particular reason?
>> 
>> This improves javac benchmark considerably (look at both wall time and user time):
>> 
>> 
>> # BEFORE
>> Benchmark 1: build/linux-x86_64-server-release/images/jdk/bin/java -XX:CacheDataStore=app.cds -Xmx256m -Xms256m -XX:+UnlockExperimentalVMOptions -XX:+UseEpsilonGC -cp JavacBenchApp.jar JavacBenchApp 50
>>   Time (mean ± σ):     348.3 ms ±   2.8 ms    [User: 949.0 ms, System: 101.4 ms]
>>   Range (min … max):   344.0 ms … 355.3 ms    100 runs
>> 
>> # AFTER
>> Benchmark 1: build/linux-x86_64-server-release/images/jdk/bin/java -XX:CacheDataStore=app.cds -Xmx256m -Xms256m -XX:+UnlockExperimentalVMOptions -XX:+UseEpsilonGC -cp JavacBenchApp.jar JavacBenchApp 50
>>   Time (mean ± σ):     312.2 ms ±   2.6 ms    [User: 577.8 ms, System: 95.4 ms]
>>   Range (min … max):   307.1 ms … 318.5 ms    100 runs
>
> src/hotspot/share/compiler/compilationPolicy.cpp line 914:
> 
>> 912:       max_task = task;
>> 913:       max_method = method;
>> 914:       break;
> 
> I think we can just return `task` here.
> 
> We don't cache `CompLevel_full_profile` Level3 C1 compiled code and as result we do nothing in the rest of this method for AOT code.
> 
> We put SCC tasks on separate queues which will have only these tasks.

Right, that makes sense. Since we want to get the SC tasks as soon as possible, it makes sense to shortcut hard. I'll do it in new commit.

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PR Review Comment: https://git.openjdk.org/leyden/pull/17#discussion_r1747979871