RFR: 8368321: Rethink compilation delay strategy for lukewarm methods [v2]

[Vladimir Ivanov]

On Wed, 22 Oct 2025 01:36:39 GMT, Igor Veresov <iveresov at openjdk.org> wrote:

>> In the current implementation we delay profiling of lukewarm methods (those that were never compiled by C2 during training) by increasing the 2->3 threshold by a factor. That may shift profiling of those too much into the future if a large factor is used, if we use a small factor, however, profiling may happen within the training run window so to speak. The solution I came up with it to delay profiling until we reach the number of invocations of a method equal to the number we had in the training run. After that we use the normal policy.
>> 
>> Here is an example. I trained our JavacBenchApp for 5 iterations (which is artificially low and therefore many methods would be classified as lukewarm). Then I ran it for 200 iterations with AOT replay.
>> 
>> <img width="640" height="480" alt="old-vs-new" src="https://github.com/user-attachments/assets/7f758dc1-ad6d-4ae5-8519-ddab18410722" />
>> 
>> While initially the performance is similar it quickly diverges. With the new approach we move to standard handling of lukewarm methods after 5 iterations and they get compiled with C2. With the old approach we don't.
>
> Igor Veresov has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix zero build

Looks good.

-------------

Marked as reviewed by vlivanov (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/27926#pullrequestreview-3378908589