ZGC: RFR: 8207756: jstat should show CGC STW phases of ZGC

[Yasumasa Suenaga]

Hi Per,


> http://cr.openjdk.java.net/~pliden/8207756/webrev.0

Thanks! It looks good to me.


> In general, I think jstat is in such a bad state that I'm hoping we long term can either deprecate/remove it or replace it with a better tool. As you know, jstat just makes too many assumptions and is a really bad fit for concurrent collectors in general.

I agree with you.

IMHO we should get GC logs to check GC working. However we can use jsnap to check GC working from core image if this issue is fixed.
This bug ticket is reported issue in jstat, but it is caused in PerfCounter. I believe this fix helps us in troubleshooting.


Yasumasa


On 2018/08/07 19:36, Per Liden wrote:
> Hi,
> 
> On 07/27/2018 04:31 PM, Yasumasa Suenaga wrote:
>> Hi Erik, Per,
>>
>> Thank you for your comment.
>> I uploaded new webrev. It has CGC counter in ZServiceability.
>>
>>    http://cr.openjdk.java.net/~ysuenaga/JDK-8207756/webrev.01/
>>
>> I know ZGC has three STW phases. They are called by VM_ZOperation. So I had added CGC counter in it at first. However I agree with you if ZServiceability should have it.
> 
> In general, I think jstat is in such a bad state that I'm hoping we long term can either deprecate/remove it or replace it with a better tool. As you know, jstat just makes too many assumptions and is a really bad fit for concurrent collectors in general. Anyway, let's just play along and try to make jstat happy for now.
> 
> I took the liberty of making some cleanups and adjustments to your patch.
> 
> http://cr.openjdk.java.net/~pliden/8207756/webrev.0
> 
> I'm currently running it through our testing.
> 
> cheers,
> Per
> 
>>
>>
>> Yasumasa
>>
>>
>> On 2018/07/26 23:19, Erik Österlund wrote:
>>> Hi Yasumasa,
>>>
>>> There is only one global instance of CollectorCounters. Do we really have to pass it around into constructors and dump it in ZDriver?
>>> I don't see why it would be in any way problematic to just put this global instance of counters in ZServiceabilityCounters. And put the TraceCollectorStats tcs(_cgc_counters); stuff in ZServiceabilityCountersTracer or something like that.
>>>
>>> Also I saw this: _cgc_counters = new CollectorCounters("Z stop-the-world phases", 2);
>>>
>>> Does this assume there are two pauses for a ZGC collection cycle? There are at least 3, but possibly more:
>>>
>>> 1) Mark start
>>> 2) Mark end (this could recur multiple times due to unlucky races with mutators resurrecting weak references right before hitting mark end, causing a new concurrent phase if a large object graph was reachable from this weak ref). So we really can't know for sure how many pauses there will be.
>>> 3) Relocate start (done after reference processing and concurrent selection of relocaiton set)
>>>
>>> Thanks,
>>> /Erik
>>>
>>> On 2018-07-26 15:44, Yasumasa Suenaga wrote:
>>>> CC'ing to hotspot-gc-dev
>>>>
>>>> Hi Per,
>>>>
>>>> I've looked at ZServiceabilityCounters in zServiceability.cpp .
>>>> IMHO it is unsuitable because CGC counter means STW in concurrent GC. So I think it is suitable to implement in VMOperation for ZGC.
>>>>
>>>> Thanks,
>>>>
>>>> Yasumasa
>>>>
>>>>
>>>> On 2018/07/26 22:30, Per Lidén wrote:
>>>>> Hi,
>>>>>
>>>>> Please have a look at the zServiceability class, which is where code like this is intended to live.
>>>>>
>>>>> /Per
>>>>>
>>>>>> On 26 Jul 2018, at 14:30, Yasumasa Suenaga <yasuenag at gmail.com> wrote:
>>>>>>
>>>>>> PING: Could you review it?
>>>>>>
>>>>>>>    webrev: http://cr.openjdk.java.net/~ysuenaga/JDK-8207756/webrev.00/
>>>>>>
>>>>>>
>>>>>> Yasumasa
>>>>>>
>>>>>>
>>>>>>> On 2018/07/18 11:59, Yasumasa Suenaga wrote:
>>>>>>> Hi all,
>>>>>>> Please review this change:
>>>>>>>    JBS: https://bugs.openjdk.java.net/browse/JDK-8207756
>>>>>>>    webrev: http://cr.openjdk.java.net/~ysuenaga/JDK-8207756/webrev.00/
>>>>>>> jstat shows CGC STW phases as CGC and CGCT fields since JDK-8153333 .
>>>>>>> However, ZGC does not adapt to it yet as following:
>>>>>>> ```
>>>>>>> $ jstat -gc 1234 1 1
>>>>>>>   S0C S1C S0U S1U EC EU OC OU MC MU CCSC CCSU YGC YGCT FGC FGCT CGC CGCT GCT
>>>>>>>    - - - - - - 514048.0 12288.0 4352.0 3731.2 0.0 0.0 - - - - - - 0.000
>>>>>>> ```
>>>>>>> I uploaded webrev which is for jdk/jdk repo. Please tell me if it
>>>>>>> should be for zgc repo.
>>>>>>> I'm not an author of ZGC. So I need a sponsor.
>>>>>>> (I'm a Reviewer of jdk. If this change should be pushed to jdk/jdk,
>>>>>>> please tell me. I will push it after reviewing.)
>>>>>>> Thanks,
>>>>>>> Yasumasa
>>>>>
>>>