RFR: 8277893: Arraycopy stress tests

[Aleksey Shipilev]

On Tue, 30 Nov 2021 20:34:46 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> My original intent was to make sure the tests cross all small page sizes (up to 64K) and maybe even some large page sizes (1M `long[]` is 8M, so 2*4M). The size of this array does not matter for test performance very much, since we only allocate two `MAX_SIZE`-d arrays per entire run. Driver even caps the heap size at `-Xmx256m` to block tests from using too much memory. So, I'd leave it at 1M, if you agree.
>
> Okay. I was concern because of times you show. I am fine with running tests upto 10-15 mins but not this:
> 
> # x86_64 (i5-11500)
>   real    41m32.622s
>   user    447m19.986s
>   sys     0m21.026s
> 
> 
> Do you know why it takes so much time on it?

That small machine has very slow memory compared to other ones. The parallelism in stress tests (9 types, 2 forked VMs each) puts that machine on its knees. There is a blurb about that effect here: https://github.com/openjdk/jdk/pull/6594/files#diff-f72fee20a49daaf4e05002372e93f426407ecd429a227393e2ec79e821042c90R40-R47 -- I don't think it would matter much if we trim `MAX_SIZE`, but I'll try tomorrow.

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PR: https://git.openjdk.java.net/jdk/pull/6594