RFR: Fix TestUnifiedLoggingSwitchStress test failure

[Zhengyu Gu]

On 06/01/2018 12:31 PM, Aleksey Shipilev wrote:
> On 06/01/2018 06:24 PM, Zhengyu Gu wrote:
>>
>>
>> On 06/01/2018 12:02 PM, Aleksey Shipilev wrote:
>>> On 06/01/2018 05:20 PM, Zhengyu Gu wrote:
>>>> The test failed due to degenerated cycle, which takes over task queue from earlier cycle. Resetting
>>>> task queue statistics under these circumstances, results assertion failures during
>>>> print_statistics().
>>>>
>>>> Webrev: http://cr.openjdk.java.net/~zgu/shenandoah/degen_tq_stats/webrev.00/
>>>
>>> What is the assert? Maybe we should do what G1 is doing, namely:
>>
>> 428   TASKQUEUE_STATS_ONLY(print_taskqueue_stats());
>>
>> will invoke TaskQueueStats::verify() and fail following assert:
>>
>>   assert(get(push) == get(pop) + get(steal),
>>           "push=" SIZE_FORMAT " pop=" SIZE_FORMAT " steal=" SIZE_FORMAT,
>>           get(push), get(pop), get(steal));
> 
> So this is because taskqueues are not quiescent yet, right?
> Well, there is due to miscounting.

> 
>>> If we still need to do what you suggest, I think we are better off using the multiline-version:
>>>
>>> #if TASKQUEUE_STATS
>>>     // Do not reset task queue statistics if we are carrying over work
>>>     // in the task queues
>>>     if (!sh->is_degenerated_gc_in_progress()) {
>>>       reset_taskqueue_stats();
>>>     }
>>> #endif
>>
>> okay: http://cr.openjdk.java.net/~zgu/shenandoah/degen_tq_stats/webrev.01/
> 
> Looks good.
> 
> But I still wonder why can't we simplify the whole thing? Remove the TQ stats block from
> SCM::mark_from_roots() completely, move reset past the print in SCM::finish_mark_from_roots()? Let
> the queues finish, and print+reset.
> 
> For example:
> 
> http://cr.openjdk.java.net/~shade/shenandoah/tq-why/webrev.01/src/hotspot/share/gc/shenandoah/shenandoahConcurrentMark.cpp.sdiff.html

I can try this, but I suspect it only works with all success cycles.

Thanks,

-Zhengyu


> 
> -Aleksey
> 
> 
>