RFR(M) Enable UseDynamicNumberOfGCThreads flag support in Shenandoah

[Roman Kennke]

Sorry, this went under the radar with FOSDEM and all.

The patch looks ok.

We should think again about killing conc-workers and simply use a
single dynamically-scaled thread pool.

Roman

Am Montag, den 06.02.2017, 16:27 -0500 schrieb Zhengyu Gu:
> Resend with proper subject line.
> 
> Thanks,
> 
> -Zhengyu
> 
> 
> 
> On 02/02/2017 07:39 AM, Zhengyu Gu wrote:
> > The heuristics for selecting number of workers probably still need
> > to 
> > be tweaked, as I did not see
> > improvement with flag on/off with SPECjbb2015.
> > 
> > The patch fixes a couple of potential issues:
> > 
> > - Without the patch, enable UseDynamicNumberOfGCThreads can crash
> > VM 
> > due to uninitialized gclab of
> >   dynamic created workers.
> > 
> > - Imbalance of task queues and workers that potential cause misses
> > of 
> > final mark. The problem is hidden
> >   because of currently implementation utilizing max parallel
> > workers 
> > for the final mark from root.
> > 
> > I would like to get this push if there are not problems with the
> > patch 
> > itself, so we can find more
> > systems to tweak the algorithm.
> > 
> > Webrev: 
> > http://cr.openjdk.java.net/~zgu/shenandoah/dynamic_workers/webrev.0
> > 0/
> > 
> > Tests:
> >   - SPECjbb2015 fastdebug and release
> >   - SPECjvm     Debry fastdebug and release
> > 
> > Thanks,
> > 
> > -Zhengyu
> > 
> 
>