8202466: Test serviceability/tmtools/jstat/GcTest01.java fails: Number of concurrent GC events is 1, but CGCT is 0

[Yasumasa Suenaga]

FYI: jdk-11-ea+11 passed GcTest01.java
   https://download.java.net/openjdk/testresults/11/archives/11/diff-hotspot-10-11.txt


On 2018/05/02 21:46, Yasumasa Suenaga wrote:
> Hi all,
> 
> I've tried to fix 8202466, but I do not yet certain which solution is the best for it.
> So I want your opinion for it.
> 
> https://bugs.openjdk.java.net/browse/JDK-8202466
> 
> David reports serviceability/tmtools/jstat/GcTest01.java failed in Mach5. It seems to appear on OS X only.
> He has shared jtreg report, and I found as below:
> 
> ```
> stdout: S0C S1C S0U S1U EC EU OC OU MC MU CCSC CCSU YGC YGCT FGC FGCT CGC CGCT GCT
>   0.0 0.0 0.0 0.0 3072.0 0.0 11264.0 2825.6 9472.0 9003.3 1024.0 845.3 26 0.204 3 0.292 1 0.000 0.497
> ```
> 
> YGCT: 0.204
> FGCT: 0.292
> CGCT: 0.000
> 
>   GCT: 0.497
> 
> I guess this failure was caused by rounding error because (YGCT + FGCT + CGCT) < GCT.
> CGC is 1, so CGC operation might finish in very short time.
> 
> 
> GcTest01.java:
>    http://hg.openjdk.java.net/jdk/jdk/file/4da7dce7e2bf/test/hotspot/jtreg/serviceability/tmtools/jstat/GcTest01.java#l57
> 
> GcCauseTest01.java:
>    http://hg.openjdk.java.net/jdk/jdk/file/4da7dce7e2bf/test/hotspot/jtreg/serviceability/tmtools/jstat/GcCauseTest01.java#l53
> 
> GcTest01 and GcCauseTest01 are very similar, but GcCauseTest01 passed.
> Both tests use GcProvoker::provokeGc() to inflate memory usage. So I wonder why GcTest01 just only failed.
> I guess we might encounter similar issue(s) in the future if we get more fast machines.
> 
> Hence I think we can take two approaches as below:
> 
>    1. Add all tests in serviceability/tmtools/jstat to ProblemList.
>    2. Change all JstatGc*Tool to use custom jstat_options - to show raw values in PerfCounters
> 
> 
> What do you think?
> I can start to work for it if they are OK.
> 
> 
> Thanks,
> 
> Yasumasa
>