RFR: Simplify parallel synchronizer roots iterator

[Roman Kennke]

Am 10.05.2017 um 16:07 schrieb Roman Kennke:
> The parallel synchronizer roots iterator is a bit too complicated for no
> good reason (I think, correct me if I'm wrong). It's doing two CASes per
> loop iteration, once over the CHAINED_MARKER/CLAIMED_MARKER in the
> block, and once more over the _cur field in the
> ParallelObjectSynchronizerIterator. I think doing a very simple CAS-loop
> over the _cur field is good enough, and maybe even improves performance
> slightly:
>
> This is what I get with gc-bench's roots.Sync benchmark:
>
> baseline:
> [15,840s][info][gc,stats]     S: Synchronizer Roots   =     0,16 s (a
> =    17334 us) (n =     9) (lvls, us =    11523,    13867,    14062,   
> 16992,    25422)
> [15,841s][info][gc,stats]     UR: Synchronizer Roots  =     0,11 s (a
> =    12206 us) (n =     9) (lvls, us =     9707,    10352,    11719,   
> 11914,    15709)
>
> patched:
> [15,463s][info][gc,stats]     S: Synchronizer Roots   =     0,15 s (a
> =    16147 us) (n =     9) (lvls, us =    11523,    12500,    15430,   
> 15820,    25440)
> [15,463s][info][gc,stats]     UR: Synchronizer Roots  =     0,10 s (a
> =    11111 us) (n =     9) (lvls, us =     9160,     9414,     9766,   
> 11523,    13777)
>
>
> http://cr.openjdk.java.net/~rkennke/simplify-sync-roots/webrev.00/
> <http://cr.openjdk.java.net/%7Erkennke/simplify-sync-roots/webrev.00/>
>
>
> As a nice bonus, this reduces diffs between upstream jdk9 and shenandoah
> jdk9 (removed CLAIMED_MARKER and cas_set_object())
>
> Testing: hotspot_gc_shenandoah, specjvm-derby, gc-bench/roots.Sync
>
> Note: gc-basher fails in hotspot_gc_shenandoah run, but doesn't seem
> related to that change.
I just noticed a leftover from some jdk8u related work in my patch.
Here's the cleaned up patch:

http://cr.openjdk.java.net/~rkennke/simplify-sync-roots/webrev.01/
<http://cr.openjdk.java.net/%7Erkennke/simplify-sync-roots/webrev.01/>

Ok now?

Roman