Request for review (s) : 8017462: G1: guarantee fails with UseDynamicNumberOfGCThreads

[Thomas Schatzl]

Hi Jon,

On Tue, 2015-03-10 at 09:26 -0700, Jon Masamitsu wrote:
> 8017462: G1: guarantee fails with UseDynamicNumberOfGCThreads
> 
> https://bugs.openjdk.java.net/browse/JDK-8017462
> 
> When fewer than the maximum number of threads was being used for
> a parallel section, phase times for the threads that did not execute and
> averages for the phase were misleading.  The fix passes the active number of
> GC threads  to the G1 phase timers.
> 
> http://cr.openjdk.java.net/~jmasa/8017462/webrev.00/
> 
> Tested with gc_test_suite.

- I would somewhat prefer if _active_threads would not be stored in
every WorkerDataArray. This seems a waste of space. G1GCPhaseTimes
already stores it, so it could easily passed to
WorkerDataArray::verify()/print() instead which seems cleaner to me.

This would also avoid the additional parameter in
note_string_dedup_fixup_start().

- WorkerDataArray::reset() is PRODUCT_RETURN. That means that in a
product VM, WorkerDataArray::_active_length is seemingly never assigned
to then as far as I can see.

- is it possible to create a test for G1 that runs with
G1LogLevel=finest and parses and verifies output of one GC phase that
takes at least some time? I.e. that you have active_workers amount of
durations in that line and the sum matches more or less.

- Bengt is currently also changing this code significantly (see the
review for 8074037: Refactor the G1GCPhaseTime logging to make it easier
to add new phases). Somebody will have to do a significant amount of
merging :/

Thanks,
  Thomas