RFR: JDK-8275608: runtime/Metaspace/elastic/TestMetaspaceAllocationMT2 too slow [v3]

[Thomas Stuefe]

On Fri, 29 Oct 2021 09:17:31 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> Small tweaks to make these elastic metaspace stress tests faster.
>> 
>> Before, runtime for individual tests was wobbling between 40+ seconds and some rare timeouts at 3+ minutes, depending on machine load and random luck. Now, we get a steadfast 35-37 seconds.
>> 
>> I tested this manually, checking the numbers that we really test what we want to test (a lot of arena activity). Also GHAs and SAP nightlies.
>> 
>> Thanks, Thomas
>
> Thomas Stuefe has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Update test/hotspot/jtreg/runtime/Metaspace/elastic/RandomAllocator.java
>    
>    Co-authored-by: Aleksey Shipilëv <shade at redhat.com>
>  - Update test/hotspot/jtreg/runtime/Metaspace/elastic/RandomAllocator.java
>    
>    Co-authored-by: Aleksey Shipilëv <shade at redhat.com>

Changes:
- Used volatile as Alexey suggested
- changed the breathe-in-and-out logic a bit. No need to count ticks on breathe in, the logic is:
  - allocate till we hit ceiling
  - deallocate a bit
  - again allocate until full
  - repeat 1000 times
This leads to a reasonable small - but not 0 - number of re-created arenas, which was the intention of this test. Beforehand, allocation threads were too often recreated, we spent too much time in thread creation and -cleanup.

I also changed the test names, because I want to be able to call them individually with '#bla' and that does not work if the subtest name contains non-alphanumerics.

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PR: https://git.openjdk.java.net/jdk/pull/6041