RFR: 8305895: Implement JEP 450: Compact Object Headers (Experimental) [v21]

[Thomas Stuefe]

On Thu, 19 Sep 2024 13:34:47 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> Do you seen any effects of this in anything other than special-crafted micro benchmarks? I wonder if it would be good enough to hard-code this to be 10 for the first integration of Lilliput.
>
> I will do some benchmarks

I did SpecJBB runs with shift of 6, 8 and 10, respectively, which amounts to Klass alignment of 64, 256 and 1K. Benchmark scores did not show a significant pattern. I did not measure CPU stats though. 

But I still think a dynamically calculated shift makes sense, and I hesitate to change this code at this point. I therefore would like to move this question to followup RFEs if necessary.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20677#discussion_r1810775878