RFR (XXS): 8202829: Implement CollectedHeap::get_safepoint_workers() for G1

[Per Liden]

Yep, looks good!

/Per

On 2018-05-09 18:52, Erik Osterlund wrote:
> Hi Thomas,
> 
> A very beneficial one-liner indeed.
> 
> Looks good!
> 
> Thanks,
> /Erik
> 
>> On 9 May 2018, at 17:15, Thomas Schatzl <thomas.schatzl at oracle.com> wrote:
>>
>> Hi all,
>>
>>   due to the recent RFR for ZGC I noticed that G1 would also benefit
>> from implementing CollectedHeap::get_safepoint_workers().
>>
>> It is a pretty trivial change for G1 as we already have/use a "hot"
>> WorkGang that is always available during a safepoint.
>>
>> CR:
>> https://bugs.openjdk.java.net/browse/JDK-8202829
>> Webrev:
>> http://cr.openjdk.java.net/~tschatzl/8202829/webrev/
>> Testing:
>> hs-tier1-3
>>
>> Results from random specjbb2015 runs:
>>
>> Baseline for "safepoint cleanup tasks":
>>               count: 1628
>>                 min: 7.5e-05
>>                 max: 0.0072682
>>                 sum: 4.76701
>>                 avg: 0.00292814 (+/-0.0016433)
>>     95th percentile: 0.0054634
>>     99th percentile: 0.0062773
>>   99.9th percentile: 0.0072269
>> 99.99th percentile: 0.0072682
>>
>> With changes for "safepoint cleanup tasks":
>>               count: 1772
>>                 min: 9.24e-05
>>                 max: 0.0014651
>>                 sum: 1.33761
>>                 avg: 0.000754861 (+/-0.000230524)
>>     95th percentile: 0.0009985
>>     99th percentile: 0.001097
>>   99.9th percentile: 0.0012676
>> 99.99th percentile: 0.0014651
>>
>> So, some significant improvement here, although very small in total.
>> Since it is such a simple change I guess we'll take it :)
>>
>> I assume in the future the number of threads could be determined more
>> cleverly depending on actual work.
>>
>> Thanks,
>>   Thomas
>>