Long pacing time seems to result in long response times

[Roman Kennke]

Hi Jeroen,

Sorry that I did not reply earlier.

> Just to let you know. We found that setting:
> -XX:ShenandoahPacingMaxDelay=10
> solved our problem.

Isn't that the default? Have you set that flag to a higher value before?

> Tuning SpikeFactor also helped a lot.

Right. Which value worked better for you?


Thanks,
Roman


>> Hi,
>>
>> In a load test on a JSF application we encountered long response times up
>> to 4 minutes instead of a few seconds, during a 20 min part of the test,
>> while putting constant load on it.  Pacing times seem large to me and I
>> want to find out if this is causing the bad response times. The CPU usage
>> on the host follows that of the jboss process which lowers from 45% to 12%
>> in that period. So it seems that the app is slowed down for about 20
>> minutes; 5 minutes the slowest and then slowly recovering.
>>
>> There is a degenerate gc for 1.4 s., triggered by a TLAB allocation
>> failure, followed by 10 s. pacing (212 ms avg non-zero). Then pacing of 28
>> ms. followed by 28 s.(!) pacing (900 ms avg non-zero).
>> *1 Is this normal pacing behavior?
>>
>> Configuration: x86-64b, 6 cores, VMWare, RHEL 7.9, OpenJDK 11.0.12, jboss
>> 7.3.3.
>> jvm settings: -XX:+UseShenandoahGC -XX:+AlwaysPreTouch -XX:+UseNUMA
>> -XX:-UseBiasedLocking -XX:+UseTransparentHugePages
>> -Xlog:gc*:file=...log/gc-%t-%p.log:tags,uptime,time,level:filecount=5,filesize=3m
>> -Xlog:safepoint*:file=...log/safepoints-%t-%p.log:tags,uptime,time,level:filecount=5,filesize=3m
>>
>> In our profiling tool it seems e.g. 88% of a long user tx (4 min) is spent
>> in locking.
>> *2. Is that how pacing shows?
>>
>> We will try out -XX:ShenandoahPacingMaxDelay=10 in a new test with also a
>> bigger heap (12->16GB).
>> *3 Would that solve the issue?
>>
>> *4 Would it help to provide gc logging here for better understanding what
>> happens?
>>
>> Kind regards,
>>
>> Jeroen Borgers
>>
>> drs. Jeroen Borgers
>> Principal Consultant
>> jPinpoint Performance Services, jpinpoint com, The Netherlands.
>>   e-mail: jborgers at jpinpoint com
>>
>