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

[Thomas Schatzl]

Hi Sangheon,

On Fri, 2015-06-05 at 15:34 -0700, 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:
> JPRT

  looks okay. Can you do a nightly run with the changes in Aurora too,
just in case?

Thanks,
  Thomas