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  1. JDK
  2. JDK-8154736

enhancement of cmpxchg and copy_to_survivor for ppc64

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    • gc
    • b17
    • arm, ppc

    Backports

      Description

        The current implementation of cmpxchg was done in a sequential consistent way.
        On PPC64, it uses a sync instruction before and one after the cmpxchg code which is the most conservative implementation.
        However, these sync instructions cause overhead because they are very expensive in the current POWER chip design.

        Proposed Enhancement (by Hiroshi H Horii):
        Callers can explicitly specify memory barriers. Default value must be conservative so it is not necessary to change all callers.

        The change will improve performance of copy_to_survivor in the parallel GC.
        copy_to_survivor changes forward pointers by using cmpxchg. This operation doesn't require any sync instructions.
        A pointer is changed at most once in a GC and when cmpxchg fails, the latest pointer is available for the caller.

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            backported by

            Backport - A issue that is required to port a Bug or Feature into another product release. This issue type is generally associated with the main Bug/Feature to represent each individual release of the port. JDK-8204788 enhancement of cmpxchg and copy_to_survivor for ppc64

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

            Bug - A problem which impairs or prevents the functions of the product. JDK-8263107 PSPromotionManager::copy_and_push_safe_barrier needs acquire memory barrier

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

            Enhancement - null JDK-8269870 PS: Membar in PSPromotionManager::copy_unmarked_to_survivor_space could be relaxed

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

            Enhancement - null JDK-8155949 Support relaxed semantics in cmpxchg

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

            Enhancement - null JDK-8204524 Unnecessary memory barriers in G1ParScanThreadState::copy_to_survivor_space

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

            Enhancement - null JDK-8205908 Unnecessarily strong memory barriers in ParNewGeneration::copy_to_survivor_space

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

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                horii Hiroshi Horii
                mdoerr Martin Doerr
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                  Created:
                  Updated:
                  Resolved: