[aarch64-port-dev ] Prefetching parameters

[Stuart Monteith]

Hello,
 I've been doing some investigation of prefetching to decide upon
reasonable parameters for each of the platforms we're testing.

The results are posted here:
   http://people.linaro.org/~stuart.monteith/Prefetch/

For each platform:

For Platform A:

    There is no benefit to allocation prefetching, and for purely
allocating arrays, it is harmful:

     -XX:AllocatePrefetchStyle=-1

    For array copy prefetching, 3 cache lines are best:
     -XX:PrefetchCopyIntervalInBytes=384

For Platform B:
    There is a large benefit to allocation prefetching smaller arrays
if they are not being used straight away. This may benefit some
workloads. Otherwise but the default should probably be:

   -XX:AllocatePrefetchStyle=-1

    For array copy prefetching, it's best to not do prefetching.


For Platform C:
   For all, except larger arrays, there aren't benefits for allocation
prefetching. For arrays that are zero'd but not used, it is best not
to turn on prefetching.

   -XX:AllocatePrefetchStyle=-1

   There is no clear benefit to array copy prefetching.

For all platforms:

    -XX:PrefetchScanIntervalInBytes

    Can be left as is - there are no clear benefits to enabling this.



Best regards,
    Stuart