G1 performance

[Srinivas Ramakrishna]

I have been playing with G1 a bit, and have noticed a nearly 10%
overhead with G1, which is independent of the measured GC overheads.
It's possible that this is because of the G1 write barriers inhibiting
certain JIT optimizations. I have also seen, although this needs to be
established more thoroughly, that G1's performance degrades the longer
it runs, in the sense that minor GC pause times become progressively
worse.

Has this kind of performance behaviour been observed by others on this
list? Or internally at Oracle in performance testing of G1? Or by
other power users of G1 out there?

Basically, all of the experiments I have done seem to indicate that
CMS performs better than G1, but unfortunately the potential
fragmentation problem with CMS (followed by the promotion failure
handling and the single-threaded compaction to follow) make it
unsuitable in certain situations.

thanks!
-- ramki