RFR (S): Conditional matrix cleanup

[Roman Kennke]

Am 03.05.2017 um 13:21 schrieb Aleksey Shipilev:
> Hi,
>
> Turns out, the significant part of per-region matrix cleanup are the actual
> stores. In most of our scenarios the matrix is very sparse, and therefore it
> helps to avoid writes by checking if matrix element is set before the store:
>   http://cr.openjdk.java.net/~shade/shenandoah/matrix-clear-conditional/webrev.01/
>
> Improves recycling and final mark times (when matrix is enabled):
>
> Before:
>
>   Recycle  =     0.86 s (a =     8447 us) (n =   102)
>     (lvls, us =     8008,     8223,     8496,     8613,     9207)
>
> After:
>
>   Recycle  =     0.52 s (a =     5076 us) (n =   102)
>     (lvls, us =     4668,     4766,     4863,     5215,     7828)
>
> Testing: hotspot_gc_shenandoah
>
> Thanks,
> -Aleksey
>
Yes!