RFR (XS): JDK-8047976: Ergonomics for GC thread counts should update the flags

[Thomas Schatzl]

Hi Sangheon,

On Fri, 2014-09-26 at 10:04 +0200, Bengt Rutisson wrote:
> Hi all,
> 
> Here's an updated webrev from Sangheon:
> 
> http://cr.openjdk.java.net/~brutisso/8047976/webrev.02/
> 
>  From Sangheon:
> 
> "This includes Thomas's comments about:
> 1) Moving value set to Arguments::set_g1_gc_flags()
> 2) Adding jtreg test for G1ConcRefinementThreads variable"

The changes in the Hotspot code look okay to me. Thanks!

Some comments about the test case code:

- There is a typo in AUTO_SELCT_THREADS_COUNT, should be
AUTO_SELECT_THREADS_COUNT I think.
- There is no need to have @build and @run lines if you do not use
special options to invoke the test afaik.

Otherwise looks okay.

Thanks,
  Thomas


> 
> Thanks,
> Bengt
> 
> 
> On 2014-09-25 11:01, Thomas Schatzl wrote:
> > Hi,
> >
> > On Thu, 2014-09-25 at 09:32 +0200, Thomas Schatzl wrote:
> >> Hi,
> >>
> >> On Wed, 2014-09-24 at 08:51 -0700, Sangheon Kim wrote:
> >>> Hi all,
> >>>
> >>> can I have reviews for the following small change to update
> >>> G1ConcRefinementThreads variable?
> >>> And also I need a sponsor for this.
> >>>
> >>> CR:
> >>> https://bugs.openjdk.java.net/browse/JDK-8047976
> >>>
> >>> Webrev:
> >>> http://cr.openjdk.java.net/~brutisso/8047976/webrev.00/
> >>> <http://cr.openjdk.java.net/%7Ebrutisso/8047976/webrev.00/>
> >> Please update the flag during argument processing, not every time the
> >> method is called.
> >>
> >> Somewhere in Arguments::set_g1_gc_flags() would be appropriate I think.
> >>
> > Please also add a jtreg test case. At least one test case that verifies
> > that with G1 the G1ConcRefinementThreads is not zero if nothing or zero
> > is passed, and another one that checks that the value passed is taken
> > over.
> >
> > The test could parse the output of -XX:+PrintFlagsFinal. The test
> > gc/arguments/TestObjectTenuringFlags.java shows how this is done.
> >
> > There is also some behavior that seems to be wrong: if you manually set
> > the number of G1ConcRefinementThreads to zero (which means
> > "automatically select"), -XX:+PrintFlagsFinal still prints
> > "G1ConcRefinementThreads := 0". Imo even in this case the output should
> > contain the actual number of threads used.
> >
> > At least if you set ConcGCThreads manually to 0, the flag is set to the
> > actual value after argument processing.
> >
> > ParallelGCThreads also shows 0 here, but I think this part of bug
> > JDK-6979279 and should be fixed there.
> >
> > Thanks,
> >    Thomas
> >
> >
>