RFR: 8247820: ParallelGC: Process strong OopStorage entries in parallel

[Stefan Karlsson]

On 2020-06-23 12:23, Kim Barrett wrote:
>> On Jun 23, 2020, at 4:23 AM, Stefan Karlsson <stefan.karlsson at oracle.com> wrote:
>>
>> Hi all,
>>
>> Please review this patch to both unify handling of all OopStorage instances and parallelize it in the root processing of the Parallel GC.
>>
>> https://cr.openjdk.java.net/~stefank/8247820/webrev.01/
>> https://bugs.openjdk.java.net/browse/JDK-8247820
>>
>> This removes the explicit enumeration of "strong" OopStorages in the Parallel GC. This is a step towards allowing the Runtime code to add new OopStorages without having to update all GCs.
>>
>> It also parallelizes the processing of the OopStorages, using the class that's being introduced in:
>> https://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2020-June/030152.html
>>
>> Tested with tier1-3
>>
>> Thanks,
>> StefanK
> 
> ------------------------------------------------------------------------------
> src/hotspot/share/gc/parallel/psScavenge.cpp
>   367     // Scavenge OopStorages
> ...
>   376     PSThreadRootsTaskClosure closure(worker_id);
>   377     Threads::possibly_parallel_threads_do(true /*parallel */, &closure);
> 
> I think it's better to do these in the other order.  Processing the
> OopStorages is very parallel, with relatively small work chunks.
> Thread processing could encounter a large thread late in the process,
> leaving the one thread processing it as the long pole, with other
> threads possibly not having much to do, other than (relatively
> expensive) stealing.
> 
> Similarly for psParallelCompact.
> 
> ------------------------------------------------------------------------------
> 
> Other than that one comment, looks good.

Updated webrev:
  https://cr.openjdk.java.net/~stefank/8247820/webrev.02.delta/
  https://cr.openjdk.java.net/~stefank/8247820/webrev.02/

> 
> Gosh, I thought that was going to be much harder. I'm guessing Leo's
> conversion of ParallelGC to use workgangs simplified things some.

:)

Thanks for reviewing,
StefanK

> 
>