RFR (S/M): 8136678: Implement adaptive sizing algorithm for IHOP

[Thomas Schatzl]

Hi all,

  I would like to ask again for reviews of this change. Since
particularly at this time code changes are frequent, keeping it up to
date poses a significant burden.

Also, after some more performance testing I got some feedback that it
might be better that the number of completed marking rounds before
actually starting to adaptively size the IHOP can be configured.

On application with large heaps it can take quite a while until the
required number of completed rounds can be reached. People would be fine
with a non-optimal prediction (very conservative) at the start.

I added an option G1AdaptiveIHOPNumInitialSamples which by default
behaves the same as before (requiring three completed markings plus a
single mixed gc) to allow that tuning.

The webrevs were update in place at
http://cr.openjdk.java.net/~tschatzl/8136678/webrev.0_to_1/ (diff)
http://cr.openjdk.java.net/~tschatzl/8136678/webrev.1/ (full)

since I did not receive any feedback on the code changes themselves.

Thanks,
  Thomas

On Fri, 2015-11-06 at 11:42 +0100, Thomas Schatzl wrote:
> Hi all,
> 
>   after Sangheon's recent comment about potential division by zero, I
> went through this change and also fixed this here.
> 
> Also, the output printed the wrong numbers (i.e.
> _allocation_rate_s.last() vs. _allocation_rate_s.oldest()).
> 
> New webrevs:
> http://cr.openjdk.java.net/~tschatzl/8136678/webrev.0_to_1/ (diff)
> http://cr.openjdk.java.net/~tschatzl/8136678/webrev.1/ (full)
> 
> Thanks,
>   Thomas
> 
> On Thu, 2015-11-05 at 10:54 +0100, Thomas Schatzl wrote:
> > Hi all,
> > 
> >   can I have reviews for this change that adds a G1IHOPControl instance
> > that adaptively adjusts the current IHOP based on allocation rate and
> > marking cycle length?
> > 
> > Instead of statically setting the IHOP value (by the user at VM
> > startup), this change adds adaptive IHOP control similar to CMS.
> > 
> > The main change is in G1IHOPControl lines 106-121, the rest is just
> > setup changes and a unit test.
> > 
> > This feature, enabled by setting G1UseAdaptiveIHOP, is disabled by
> > default for now. It is planned to be enabled by default in JDK-8136680,
> > when more thorough testing has been conducted by SQE.
> > 
> > Generally it boosts G1 throughput significantly due to the low IHOP
> > default value of 45, which with that change typically gets >70, if not
> > up to 80-90, decreasing pause times significantly.
> > 
> > It depends on JDK-8136681 which is also out for review.
> > 
> > CR:
> > https://bugs.openjdk.java.net/browse/JDK-8136678
> > Webrev:
> > http://cr.openjdk.java.net/~tschatzl/8136678/webrev/
> > Testing:
> > jprt, vm.gc with G1UseAdaptiveIHOP disabled and enabled, unit test
> > 
> > Thanks,
> >   Thomas
> > 
> > 
> 
>