Scan Queue splitting defaults

[amicic]

Simplify the heuristic for Marking and Scavenge Scan Queue splitting
defaults.

The rule is simple: one queue per 8 GC threads, which is less than what
we now use, especially for low number of threads.

This rule has already been used for allocation lock splitting with
success, for a long time.

Some more additional stress testing with Scavenger with 4x smaller
workunit (32K cache size) has been performed and no regression (lock
contention causing longer GC times) was seen.

Potential benefit of this simplification is that the cost of checking if
the global cache/packet pool is full/empty will be much lower, what will
be important for Concurrent Scavenge that will used this info as an scan
loop exit criteria.

Signed-off-by: Aleksandar Micic amicic@ca.ibm.com

[amicic]

@dmitripivkine please, take a look

[amicic]

@youngar or @rwy0717, please proceed with further review

[rwy7]

@genie-omr build all

[youngar]

The AIX build failed do to a known infrastructure issue, details are on the OMR slack.

16:27:20  Scanning dependencies of target omrutiltest
16:27:20  ld: 0711-415 WARNING: Symbol omrsig_primary_signal is already exported.
16:27:20  ld: 0711-415 WARNING: Symbol omrsig_handler is already exported.
16:27:20  ld: 0711-415 WARNING: Symbol signal is already exported.
16:27:20  ld: 0711-415 WARNING: Symbol omrsig_primary_sigaction is already exported.
16:27:20  ld: 0711-415 WARNING: Symbol sigaction is already exported.
16:27:20  ld: 0711-415 WARNING: Symbol sigset is already exported.
16:27:20  ld: 0711-415 WARNING: Symbol sigignore is already exported.
16:27:20  ld: 0711-415 WARNING: Symbol bsd_signal is already exported.
16:27:20  ld: 0711-415 WARNING: Symbol sysv_signal is already exported.
16:27:20  ld: 0711-317 ERROR: Undefined symbol: .pthread_sigmask