RFR (jdk10): JDK-8180175: ObjectSynchronizer only needs to iterate in-use monitors

[Robbin Ehn]

Adding gc list.

Thanks!

/Robbin

On 05/11/2017 12:08 PM, Roman Kennke wrote:
> Hi,
> 
> ObjectSynchronizer::oops_do() currently iterates all monitor blocks,
> even free ones. With -XX:+MonitorInUseLists, each thread has its own
> in-use monitors list, and ObjectSynchronizer has a global gOmInUseList
> for moribund threads. Iterating over in-use monitors only significantly
> inmproves scanning time for monitors, because it avoids scanning free
> blocks, improves caching (no padding, and better chances to have
> thread-local oops in cache already).
> 
> Performance-wise it makes a very significant difference (running
> gc-bench's roots.Sync test, which exaggerates synchronizer usage, with
> Shenandoah):
> 
> baseline:
> S: Thread Roots 37748 us
> S: Synchronizer Roots 15115 us
> UR: Thread Roots 24967 us
> UR: Synchronizer Roots 11906 us
> 
> patched:
> S: Thread Roots 40365 us
> S: Synchronizer Roots 0 us
> UR: Thread Roots 24459 us
> UR: Synchronizer Roots 0 us
> 
> Testing: hotspot_gc, specjvm, jcstress -m quick
> 
> http://cr.openjdk.java.net/~rkennke/8180175/webrev.00/
> <http://cr.openjdk.java.net/%7Erkennke/8180175/webrev.00/>
> 
> Roman
> 
>