lock contention on parallel COPY ?

I'm currently playing with Andrews parallel restore patch and it seems 
that pg is far from taking advantage of the hardware I have for testing 
(Dual Quad Core Xeon attached to Netapp with 68 spindles). with a 
concurrency of 4 - I see iowait hovering ~1% CPU load at 20% peak and 
around 150000 contextswitches/s. The load seems to progress at around 
the same rate as a single backend restore does on the same box. a 
profile during the load (a fair amount of tables sized ~10-30M rows 
each) looks fairly similiar to:


samples  %        symbol name
1933314  21.8884  LWLockAcquire
1677808  18.9957  XLogInsert
848227    9.6034  LWLockRelease
414179    4.6892  DoCopy
332633    3.7660  CopyReadLine
266580    3.0181  UnpinBuffer
221693    2.5099  heap_formtuple
176939    2.0033  .plt
171842    1.9455  PinBuffer
160470    1.8168  GetNewObjectId
154095    1.7446  heap_insert
151813    1.7188  s_lock
117849    1.3343  LockBuffer
109530    1.2401  hash_search_with_hash_value
102169    1.1567  PageAddItem
91151     1.0320  pg_verify_mbstr_len
82538     0.9345  CopyGetData


using --truncate-before-load seems to help a bit but it still seems to 
only barely utilizing the available resources.


Stefan