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  1. JDK
  2. JDK-8152438

Threads may do significant work out of the non-shared overflow buffer

    Details

    • Subcomponent:
      gc
    • Resolved In Build:
      b127

      Backports

        Description

        Some task queue statistics measurements on BigRamTester (attached) indicate that particularly during mixed gcs a significant part of the gc threads operate out of the local overflow buffer, and in many cases also do so while the shared task queue is not completely full or even completely empty, disallowing other threads to steal and distribute work.

        BigRamTester run options -Xlog:gc*=debug,gc+phases+task=trace,gc+task+stats=trace,gc+refine=info:x.log -Xms20G -Xmx20G BigRamTester on a 2x10x2 machine.

        Look at the attached log file for the task queue stats, particularly the new columns snotfull (indicating that we popped from the overflow queue while the shared queue has not been full) and sempty (indicating that we popped from the overflow queue while shared queue has been empty).

        Relevant patches attached.
        1. 8152438-fix-push-overflow-into-shared-first
          2 kB
          Thomas Schatzl
        2. BigRamTester.java
          7 kB
          Thomas Schatzl
        3. enable-taskqueue-stats
          0.5 kB
          Thomas Schatzl
        4. improved-taskqueue-stats
          2 kB
          Thomas Schatzl
        5. x.log
          584 kB
          Thomas Schatzl

          Issue Links

            Activity

            Hide
            tschatzl Thomas Schatzl added a comment -
            Making it P4 because I have no idea about the impact yet. For BigRamTester there does not seem to be a correlation between these numbers and e.g. termination attempts.
            Show
            tschatzl Thomas Schatzl added a comment - Making it P4 because I have no idea about the impact yet. For BigRamTester there does not seem to be a correlation between these numbers and e.g. termination attempts.
            Hide
            tschatzl Thomas Schatzl added a comment -
            Bumping priority. Reports indicate that the attached change increases overall throughput by 200% on real-world huge systems.
            Show
            tschatzl Thomas Schatzl added a comment - Bumping priority. Reports indicate that the attached change increases overall throughput by 200% on real-world huge systems.
            Hide
            tschatzl Thomas Schatzl added a comment -
            Attached patch tries to refill the current queue from overflow queue if there is some space there first instead of directly processing the elements from the overflow queue.
            Show
            tschatzl Thomas Schatzl added a comment - Attached patch tries to refill the current queue from overflow queue if there is some space there first instead of directly processing the elements from the overflow queue.
            Hide
            kvn Vladimir Kozlov added a comment -
            Thomas, can you put link to review thread? Thanks!
            Show
            kvn Vladimir Kozlov added a comment - Thomas, can you put link to review thread? Thanks!
            Show
            tschatzl Thomas Schatzl added a comment - Review thread link: http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2016-May/018147.html
            Hide
            hgupdate HG Updates added a comment -
            URL: http://hg.openjdk.java.net/jdk9/hs/hotspot/rev/07109ac130cd
            User: tschatzl
            Date: 2016-06-22 09:42:13 +0000
            Show
            hgupdate HG Updates added a comment - URL: http://hg.openjdk.java.net/jdk9/hs/hotspot/rev/07109ac130cd User: tschatzl Date: 2016-06-22 09:42:13 +0000
            Hide
            hgupdate HG Updates added a comment -
            URL: http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/07109ac130cd
            User: amurillo
            Date: 2016-07-08 20:16:41 +0000
            Show
            hgupdate HG Updates added a comment - URL: http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/07109ac130cd User: amurillo Date: 2016-07-08 20:16:41 +0000

              People

              • Assignee:
                tschatzl Thomas Schatzl
                Reporter:
                tschatzl Thomas Schatzl
              • Votes:
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                Dates

                • Created:
                  Updated:
                  Resolved: