[aarch64-port-dev ] RFR: 8151340: aarch64: prefetch the destination word for write prior to ldxr/stxr loops.

[Felix Yang]

Hi,

    Please review the following webrev:
        http://cr.openjdk.java.net/~fyang/8151340/webrev.00/

    JIRA issue:
        https://bugs.openjdk.java.net/browse/JDK-8151340

    As discussed in LKML:
http://lists.infradead.org/pipermail/linux-arm-kernel/2015-July/355996.html,
the cost of changing a cache line
from shared to exclusive state can be significant on aarch64 cores,
especially when this is triggered by an exclusive store, since it may
result in having to retry the transaction.
    This patch makes use of the "prfm" instruction to prefetch cache lines
for write prior to ldxr/stxr loops.  Is it OK?

Thanks,
Felix