RFR: 8281318: Improve jfr/event/allocation tests reliability

[Aleksey Shipilev]

On Mon, 7 Feb 2022 10:19:10 GMT, Markus Grönlund <mgronlun at openjdk.org> wrote:

>> This fixes the failure on x86_32 by resolving an object/TLAB "sizing" problem. On x86_32, the 100K object gets 200K TLAB, which allocates the next object exactly in the same TLAB. Bumping the object size to 128K resolves this.
>> 
>> Additionally, rewired the tests to match object sizes exactly. In modern JDK, the header size depends on `UseCompressedClassPointers`, not on `UseCompressedOops`. Using `Whitebox`, we can poll the VM configuration exactly.
>> 
>> Additional testing: 
>>  - [x] Linux x86_32 fastdebug, `jfr/event/allocation/`
>>  - [x] Linux x86_64 fastdebug, `jfr/event/allocation/`, out of the box
>>  - [x] Linux x86_64 fastdebug, `jfr/event/allocation/`, with `-XX:-UseCompressedClassPointers`
>
> Looks good, thank you Aleksey.

@mgronlun, I am going to integrate with just your review, OK?

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PR: https://git.openjdk.java.net/jdk/pull/7365