jstat LGCC column shows

Yasumasa Suenaga suenaga.yasumasa at oss.ntt.co.jp
Tue Jan 25 01:02:37 UTC 2011


Hi,

I made a patch for resolving this problem and attached it to this email.
I hope to discuss this problem.


Thanks.

(2011/01/04 13:11), Yasumasa Suenaga wrote:
> Hi,
> 
> I ran SPECjvm2008 with OpenJDK6 provided by Fedora14 and Ubuntu 10.10 .
> I got following messages when I attached jstat to that VM with "-gccause" option:
> 
> ------------
> root at ubuntu10:~# jstat -gccause 8411 500
>    S0     S1     E      O      P     YGC     YGCT    FGC    FGCT     GCT    LGCC                 GCC
>    0.00   0.00  12.11  12.65  31.36      1    0.005     2    0.037    0.042 System.gc()          No GC
>    0.00   0.00  12.11  12.65  31.36      1    0.005     2    0.037    0.042 System.gc()          No GC
> 
>     -- snip --
> 
>    0.00   0.00  76.81  12.65  31.58      1    0.005     2    0.037    0.042 System.gc()          No GC
>   42.20   0.00   0.00  12.65  33.10      4    0.011     2    0.037    0.047 unknown GCCause      No GC
>   91.06   0.00   0.00  15.12  34.10     10    0.019     2    0.037    0.056 unknown GCCause      No GC
> 
>     -- snip --
> 
> ------------
> 
> "LGCC" column shows "unknown GCCause".
> I want to get "REAL" last gccause (I want to know what happened in VM, relating to GC).
> (In this case, I guess that LGCC shows "Allocation Failure".)
> 
> 
> I found the comment in constructor of VM_GC_Operation class as following:
> (OpenJDK7 (HS20) and OpenJDK6(HS19) are similar.)
> 
> ------------
>      // A subclass constructor will likely overwrite the following
>      _gc_cause           = GCCause::_no_cause_specified;
> ------------
> 
> 
> I checked constructor of subclass of VM_GC_Operation, and following classes do not
> initialize "_gc_cause" member:
> 
>   - VM_HeapDumper
>   - VM_GC_HeapInspection
>   - VM_GenCollectForAllocation
>   - VM_G1OperationWithAllocRequest
>   - VM_ParallelGCFailedAllocation
>   - VM_ParallelGCFailedPermanentAllocation
> 
> I think that we should initialize "_gc_cause" in constructor of these classes.
> 
> 
> Best regards,
> 
> 


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