JDK-6923991 : G1: improve scalability of RSet scanning
  • Type: Bug
  • Status: Resolved
  • Resolution: Fixed
  • Component: hotspot
  • Sub-Component: gc
  • Priority: P2
  • Affected Version: hs16
  • OS: generic
  • CPU: generic
  • Submit Date: 2010-02-05
  • Updated Date: 2013-09-18
  • Resolved Date: 2010-03-02
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JDK 6 JDK 7
6u21Resolved 7Fixed
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Description
G1 shows poor load balancing and high contention behavior during RSet scanning on CMT machines as well as on many-core x86. Previously implemented exponential skipping has unacceptable performance when it comes to extremely large processor count.

Comments
EVALUATION ChangeSet=http://hg.openjdk.java.net/jdk7/hotspot-gc/hotspot/rev/0414c1049f15,ChangeRequest=6923991
2010-02-12

EVALUATION See Description / Suggested Fix.
2010-02-11

SUGGESTED FIX The fix would be to implement block-based work stealing in rset scanning phase. It is also required to get rid of copying during this phase and postpone it until the main copying phase. This would also get rid of the buffering that significaly contributes to the observed imbalance.
2010-02-05