RFR(S): 7068240: G1: Long "parallel other time" and "ext root scanning" when running specific benchmark

John Cuthbertson john.cuthbertson at oracle.com
Fri Jul 29 17:01:53 UTC 2011

Hi Everyone,

I'm still looking for another review of this webrev.



On 07/20/11 15:45, John Cuthbertson wrote:
> Hi Everyone,
> Can I have a couple of volunteers look over these changes? The webrev 
> can be found at: http://cr.openjdk.java.net/~johnc/7068240/webrev.0/
> Description:
> When running a specific benchmark, it was noticed that the "ext root 
> scanning" time was significantly longer for one thread than the others 
> - in a good number of the evacuation pauses. Some of these long times 
> were caused by the stack depth on an application thread but others 
> were caused by the scanning of the reference processor's discovered 
> lists. Furthermore the scanning of the discovered lists was taking 
> place after RSet updating and scanning, negating any stealing that 
> might take place in these parts, and causing longer termination times. 
> Also the scan closures were applied directly to the discovered lists 
> rather than a BufferingOopClosure being applied. As a result, if any 
> copying took place, the time for that copying was being attributed to 
> ext. root scanning rather than "object copying".
> Additionally I also removed a couple statistic variables from 
> G1CollectorPolicy that were not thread-local but being updated and 
> (overwritten) by the parallel worker threads. The only place where 
> these statistic variables were being used was in an instrumentation 
> block that was executed when G1PolicyVerbose was set appropriately.
> Testing: gc test suite and jprt.
> Thanks,
> JohnC

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