RFR: Utilize parallel workers for GC tasks during safepoints

[Roman Kennke]

Am Montag, den 21.11.2016, 07:25 -0500 schrieb Zhengyu Gu:
> Hi Roman,
> 
> Thank you for the reviewing.
> 
> Coming out of concurrent phase, all queues should be empty.
> So at final mark phase, N par == N queue.

Duh. Ok :-)

But I have one more comment: in weak_refs_work() you explicitely
balance the queues. As far as I know, this should happen automatically
if you set up the ReferenceProcessor correctly. You currently set it up
for max_workers for both processing and discovery, but it should be
conc_workers for discovery and par_workers for processing. Right? 

Infact, I think we probably don't need a global ReferenceProcessor, it
could be set up before each marking cycle, and also could be set up
differently for mark-compact (where we want both discovery and
processing to use par-workers, and atomic discovery too).

/Roman

> (final_mark_loop(), it actually does not need to claim_next(),
> I should convert that to assert(extra_queue->is_empty() ....)


> 
> 
> -Zhengyu
> 
> 
> On 11/21/2016 05:47 AM, Roman Kennke wrote:
> > 
> > Hi Zhengyu,
> > 
> > I like it!
> > 
> > For going from N par threads to M conc threads, you let the conc
> > threads claim the extra queues. For the other direction (i.e.
> > final-
> > mark), are you relying on stealing to see the extra par queues?
> > Fine to commit.
> > 
> > /Roman
> > 
> > Am Freitag, den 18.11.2016, 14:27 -0500 schrieb Zhengyu Gu:
> > > 
> > > The change allows Shenandoah GC to utilize parallel GC workers
> > > during
> > > STW safepoints, without the restriction imposed by the number of
> > > concurrent GC threads.
> > > 
> > > The main purpose of the change is to allow us scale up/down GC
> > > concurrent and parallel workers independently.
> > > 
> > > Webrev: http://cr.openjdk.java.net/~zgu/shenandoah/workers/webrev
> > > .00/
> > > 
> > > 
> > > Tests:
> > > 
> > > - jcstress (fastdebug)
> > > - Shenandoah GC test (fastdebug and release)
> > > - SPECjbb (fastdebug and release)
> > > - SPECjvm (fastdebug)
> > > 
> > > 
> > > Thanks,
> > > 
> > > -Zhengyu
> > > 
>