RFR: 8079275: Remove CollectedHeap::use_parallel_gc_threads
Stefan Karlsson
stefan.karlsson at oracle.com
Thu May 7 05:52:14 UTC 2015
On 2015-05-07 02:03, Jon Masamitsu wrote:
> Stefan,
>
> Looks good.
>
> Reviewed.
Thanks, Jon.
StefanK
>
> Jon
>
> On 5/5/2015 1:16 AM, Stefan Karlsson 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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