RFR: 8079275: Remove CollectedHeap::use_parallel_gc_threads

Stefan Karlsson stefan.karlsson at oracle.com
Thu May 7 05:52:34 UTC 2015


On 2015-05-07 04:30, Srinivas Ramakrishna wrote:
> Looks good to me too.

Thanks, Ramki.

StefanK

> -- Ramki
>
> ysr1729
>
>> On May 5, 2015, at 01:16, Stefan Karlsson <stefan.karlsson at oracle.com> wrote:
>>
>>
>>
>>> On 2015-05-05 10:12, Stefan Johansson wrote:
>>> Hi Stefan,
>>>
>>>> On 2015-05-04 17:52, Stefan Karlsson wrote:
>>>> Hi,
>>>>
>>>>> On 2015-05-04 17:28, Stefan Johansson wrote:
>>>>> Hi Stefan,
>>>>>
>>>>>> On 2015-05-04 15:34, Stefan Karlsson wrote:
>>>>>> Hi,
>>>>>>
>>>>>> Please review this patch to remove CollectedHeap::use_parallel_gc_threads.
>>>>>>
>>>>>> http://cr.openjdk.java.net/~stefank/8079275/webrev.01/
>>>>> Change looks good, nice cleanup.
>>>>>
>>>>> If I'm not missing anything you could remove the typedef in concurrentMarkSweepGeneration.cpp:
>>>>>      typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
>>>>> -    _par_gc_thread_states =
>>>>> -      NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
>>>>> +  _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
>>>>>
>>>>> The typedef is only used for in the NEW_C_HEAP_ARRAY-call and I can't see any good reason for keeping it.
>>>> OK. I removed it. I also removed the unused _modUnionClosure.
>>>>
>>>> http://cr.openjdk.java.net/~stefank/8079275/webrev.02.delta/
>>>> http://cr.openjdk.java.net/~stefank/8079275/webrev.02/
>>> Looks good,
>> Thanks, Stefan.
>>
>> StefanK
>>
>>> StefanJ
>>>> Thanks,
>>>> StefanK
>>>>
>>>>> Thanks,
>>>>> Stefan
>>>>>
>>>>>> https://bugs.openjdk.java.net/browse/JDK-8079275
>>>>>>
>>>>>> This function is used from:
>>>>>>
>>>>>> 1) CMS - CMS can't be started with -XX:ParallelGCThreads=0 anymore, so all checks against use_parallel_gc_threads will always be true.
>>>>>>
>>>>>> 2) GenCollectedHeap::process_roots - This usage could be replaced with n_par_threads(), the same check the other parallel task (Threads::possibly_parallel_oops_do) uses.
>>>>>>
>>>>>> This will change the executed code for CMS but not Serial.
>>>>>>
>>>>>> Serial will always return false for CollectedHeap::use_parallel_gc_threads and GenCollectedHeap:n_par_threads(). See:
>>>>>> void GenCollectedHeap::set_par_threads(uint t) {
>>>>>>   assert(t == 0 || !UseSerialGC, "Cannot have parallel threads");
>>>>>>   CollectedHeap::set_par_threads(t);
>>>>>>
>>>>>> CMS will always return true for CollectedHeap::use_parallel_gc_threads, but can now return either true or false for n_par_threads() depending on how n_par_threads was setup for the currently executing task. This means that some CMS paths will now call StringTable::oops_do instead of StringTable::possibly_parallel_oops_do, when running single threaded.
>>>>>>
>>>>>> Thanks,
>>>>>> StefanK



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