RFR (S): 8079555: REDO - Determining the desired PLAB size adjusts to the the number of threads at the wrong place

Jon Masamitsu jon.masamitsu at oracle.com
Mon Jul 6 21:18:03 UTC 2015


Changes look good.


On 06/05/2015 03:34 PM, sangheon.kim wrote:
> Hi all,
> Please review this REDO change to determine the desired PLAB size for 
> current gc worker threads.
> The reason for back out of previous 
> change(https://bugs.openjdk.java.net/browse/JDK-8073204) was it 
> wouldn't guarantee to be '>= PLAB minimum size'. So added 
> MAX2(min_size(),) to guarantee that.
> Currently we calculate an optimal PLAB size with current number of gc 
> workers.
> When the number of workers changes dynamically 
> (-XX:+UseDynamicNumberOfGCThreads), the desired PLAB size returned(by 
> desired_plab_sz()) is still tuned to the number of gc workers that has 
> been used previously.
> This change is, firstly calculate the desired PLAB value for a single 
> gc worker and then return desired PLAB size which is bigger(or equal) 
> than PLAB min size according to the current number of threads.
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8079555
> Webrev:
> http://cr.openjdk.java.net/~sangheki/8079555/webrev.00/
> Test:
> Thanks,
> Sangheon

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