RFR(S): 8229422: Taskqueue: Outdated selection of weak memory model platforms

[Thomas Schatzl]

Hi,

On 15.08.19 18:28, Doerr, Martin wrote:
> Hi Derek,
> 
> thanks for pointing me to the aarch64 issue and paper.
> I have added a link to that issue.
> 
>> There changes around CPU_NOT_MULTIPLE_COPY_ATOMIC in
>> src/hotspot/share/utilities/globalDefinitions.hpp are not simply a change to
>> GC behavior for S390, but are changing interpreter and compiler behavior
>> arm32 (and maybe Aarch64?).
> 
> My initial webrev is only a functional change for s390.
> 
> Current implementation:
> - CPU_NOT_MULTIPLE_COPY_ATOMIC is only used to control the following:
>    support_IRIW_for_not_multiple_copy_atomic_cpu: only true on PPC64
> - TaskQueue uses fence on all platforms except SPARC and x86
> 
> My webrev:
> - Still:
>    support_IRIW_for_not_multiple_copy_atomic_cpu: only true on PPC64
> - TaskQueue uses fence on all platforms except SPARC, x86 and s390

Maybe the comments above the define seem superfluous: they do not add 
more information. Same for the "we don't have this property" comments. 
Otherwise I would prefer something like "<platform> is [not] multiple 
copy atomic", but that would only repeat the code just below.

I would tend to just remove the comments; I do not need to see another 
webrev for just such a comment removal.

Note sure if making support_IRIW_for_not_multiple_copy_atomic_cpu 
another define makes the code better.

Also thanks for moving the other ideas pointed out to separate RFRs.

Thanks,
   Thomas