JDK-6786503 : Overflow list performance can be improved
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: 5.0u15,5.0u16
  • Priority: P3
  • Status: Closed
  • Resolution: Fixed
  • OS: generic,windows_2003
  • CPU: generic,x86
  • Submitted: 2008-12-17
  • Updated: 2011-03-07
  • Resolved: 2011-03-07
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Other Other JDK 6 JDK 7 Other
5.0u18-rev,hs11.3Fixed 5.0u19Fixed 6u13-revFixed 7Fixed hs11.3Fixed
Related Reports
Relates :  
Relates :  
The expected complexity for completely draining a long list
can be reduced from quadratic  to linear time when the
contention is low. The current code causes quadratic
complexity even when there is no contention for the overflow list.

Should check other collectors to see if the same problem
exists in any of the other collectors (in particular ParNew
which also uses overflow lists in somewhat similar fashion).

EVALUATION http://hg.openjdk.java.net/jdk7/hotspot-gc/hotspot/rev/5cfd8d19e546

SUGGESTED FIX Preliminary shape of the changes (by no means final):- http://analemma.sfbay.sun.com/net/neeraja/export/ysr/overflow/webrev

EVALUATION The same problem exists in ParNew and CMS. A patch for the fix has been generated and performance tests are currently in progress to assess the impact in low contention and high contention scenarios. (Some policy tweaks may be necessary once initial performance numbers are in.) A test binary will be made available for performance testing by customer.