RFR (S): 8148099: Improve memory access to FromCardCache during GC

[Bengt Rutisson]

Hi Thomas,

On 2016-03-31 12:25, Thomas Schatzl wrote:
> Hi all,
>
>    can I have reviews for this change that improves memory access to the
> from card cache during the GC pauses?
>
> Instead of having an array that is #threads times #regions, use a
> #regions times #threads layout. This changes the access pattern during
> clearing the entries for a particular region when it is freed from many
> single accesses with a large stride to linear memory writes.
>
> This statistically significantly improves performance of the entire
> affected phase (free cset) on large machines (large # of threads, and
> particularly many regions in the collection set).
>
> During the mutator phase there is no difference (it is lost in the
> noise), as all accesses during that time are single-element read/write
> anyway.
>
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8148099
> Webrev:
> http://cr.openjdk.java.net/~tschatzl/8148099/webrev/

Looks good.

Thanks,
Bengt

> Testing:
> jprt, vm.gc, some internal micro-benchmarks. Running for a long time
> (long before the CR has been filed) on many internal builds and
> benchmark runs.
>
> Thanks,
>    Thomas
>