JDK-8232575 : Shenandoah: asynchronous object/region pinning
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: 8-shenandoah,11-shenandoah,14
  • Priority: P3
  • Status: Resolved
  • Resolution: Fixed
  • Submitted: 2019-10-17
  • Updated: 2019-10-28
  • Resolved: 2019-10-21
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JDK 14
14 b20Fixed
Related Reports
Blocks :  
JDK-8232802 - Shenandoah: transition between "cset" and "pinned_cset" does not require cancelled gc
Sub Tasks
JDK-8236245 :  
Release Note: Shenandoah: asynchronous object/region pinning - Resolved
Description
Originally reported here:
 https://mail.openjdk.java.net/pipermail/shenandoah-dev/2019-October/010772.html

The easiest reproducer is this:
  https://cr.openjdk.java.net/~shade/8232575/GZIPUncompressBench.java
  https://cr.openjdk.java.net/~shade/8232575/benchmarks.jar

With current jdk/jdk:

Parallel, 1 thread:    111.951 �� 4.628  us/op 
Parallel, 16 threads:  149.951 �� 3.555  us/op
Shenandoah, 1 threads:   141.543 �� 0.280  us/op
Shenandoah, 16 threads: 1451.914 �� 51.406  us/op ; <---- huge scalability bottleneck

This is ruled to be the contention on the lock that guards the transition to "Pinned" state for the region. Shenandoah can be much smarter about that.

With this proof-of-concept patch:
 https://cr.openjdk.java.net/~shade/8232575/webrev.01/

Shenandoah, 1 threads: 111.997 �� 3.213  us/op  ; <--- matches Parallel
Shenandoah, 16 threads:   151.777 �� 3.511  us/op <--- matches Parallel
Comments
URL: https://hg.openjdk.java.net/jdk/jdk/rev/765ecbffe88a User: shade Date: 2019-10-21 13:12:21 +0000
21-10-2019
RFR: https://mail.openjdk.java.net/pipermail/shenandoah-dev/2019-October/010794.html
18-10-2019