Customer has 16 processor Solaris server configured with as follows:
- Processor set 1: 11 processors
- Default processor set: 5 processors
A java application was started in the deafult processor set. The following command was executed to list number of processors allocated to parallelGC.
$ jinfo -flag ParallelGCThreads 10993 (where 10993 was the pid)
jinfo response: -XX:ParallelGCThreads=13
This indicates all 16 procesors were used to calculate the default number of processors to allocate to parallel GC. The algorithm used for this calculation is:
(ncpus <= 8) ? ncpus : 3 + ((ncpus * 5) / 8)
The correct answer should have been 5 processors based on a value of ncpus of 5 available in the default processor set.
Fix requires the no of GC threads to be adjusted based on os::active_processor_count() available to the unbound Java process.