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  1. JDK
  2. JDK-8162929

Enqueuing dirty cards into a single DCQS during GC does not scale

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    • gc
    • b07

    Description

      While looking at some more demanding large microbenchmarks (e.g. BigRamtester, 20g heap, 1M regions) enqueueing dirty cards during GC in G1ParScanThreadState::update_rs incurs a significant amount of wait (idle) time.

      The reason is that enqueuing completed buffers takes a global lock (basically ending up in PtrQueue::handle_zero_index() and PtrQueueSet::enqueue_complete_buffer(); there is also some strange locking/unlocking going on in PtrQueue::locking_enqueue_completed_buffer()).

      That does not scale beyond a few threads.

      The problem is harder than it seems because after providing a per-thread DCQS, performance does not improve a lot. The stalling is moved to the malloc() calls done when allocating new DCQ buffers.

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          Enhancement - null JDK-8227719 G1 Pending cards estimation too conservative in cost prediction

          • P4 - Minor loss of function, or other problem where easy workaround is present.
          • Resolved
          relates to

          Enhancement - null JDK-8209974 Eliminate shared PtrQueues

          • P4 - Minor loss of function, or other problem where easy workaround is present.
          • Resolved

          Enhancement - null JDK-8212826 Make PtrQueue free list lock-free

          • P4 - Minor loss of function, or other problem where easy workaround is present.
          • Resolved

          Enhancement - null JDK-8230327 Make G1DirtyCardQueueSet free-id init unconditional

          • P4 - Minor loss of function, or other problem where easy workaround is present.
          • Resolved

          Enhancement - null JDK-8230332 G1DirtyCardQueueSet _notify_when_complete is always true

          • P4 - Minor loss of function, or other problem where easy workaround is present.
          • Resolved

          Enhancement - null JDK-8237143 Eliminate DirtyCardQ_cbl_mon

          • P4 - Minor loss of function, or other problem where easy workaround is present.
          • Resolved

          Enhancement - null JDK-8258142 Simplify G1RedirtyCardsQueue

          • P4 - Minor loss of function, or other problem where easy workaround is present.
          • Resolved

          Enhancement - null JDK-8076584 Parallelism used for redirty logged cards needs better control.

          • P2 - Crashes, loss of data, severe memory leak.
          • Open

          Enhancement - null JDK-8173211 G1: Enqueuing dirty cards during reference enqueuing in phase 3 does not scale

          • P4 - Minor loss of function, or other problem where easy workaround is present.
          • Resolved

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              kbarrett Kim Barrett
              tschatzl Thomas Schatzl
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                Updated:
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