RFR (S): 8150629: Initializing all ParScanThreadStates causes significant unaccounted "Other" times

Mikael Gerdin mikael.gerdin at oracle.com
Thu Feb 25 15:53:31 UTC 2016

Looks good to me too.

On 2016-02-25 16:46, Jon Masamitsu wrote:
> Change looks good.
> Jon
> On 2/25/2016 5:35 AM, Thomas Schatzl wrote:
>> Hi all,
>>    some recent measurements on large # threads and large heap machines
>> (like hundreds of threads, and high double-digit GB area) showed that
>> initializing the ParScanThreadStates takes a few milliseconds of time
>> in the VM thread (which only shows as unaccounted "Other" time).
>> This is because the work that needs to be done is O(#threads *
>> #size(young gen)), which is just getting worse the larger machines we
>> run G1 with.
>> The fix pursued in this change is to let the worker threads lazily
>> allocate and initialize the PSS instances. The way it is implemented,
>> it also allows more dynamic use of PSS instances, i.e. ones that are
>> not used for some reason are never allocated, initialized, and later
>> merged with the global statistics.
>> CR:
>> https://bugs.openjdk.java.net/browse/JDK-8150629
>> Webrev:
>> http://cr.openjdk.java.net/~tschatzl/8150629/webrev
>> Testing:
>> jprt, local benchmark runs
>> Thanks,
>>    Thomas

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