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

[Jon Masamitsu]

On 3/10/2015 11:45 AM, Thomas Schatzl wrote:
> 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.

I'd like to address this with a separate CR.  Would that be satisfactory?

Jon

>
> - 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
>
>