Pre-allocating Extents for Instances

Question

Using 10.2.0.4 Standard Edition RAC. I have a table very busy with inserts. Oracle waits for events "gc current block busy", "gc buffer busy release" etc. There seems contention of the blocks between instance. I pre-allocated extent to each instance:
alter table busy_table allocate extent (100m instance 1);
alter table busy_table allocate extent (100m instance 2);But this seems not reducing the events. Is there any more to do?
Some additional questions:
1) How to I know the extent is allocated to a specific instance? DBA_EXTENTS has no instance information. And X$KTFBUE always shows the current instance.
select INST_ID, KTFBUEFNO, KTFBUEBNO from X$KTFBUE
where KTFBUESEGBNO=(
select header_block from dba_segments
where segment_name='BUSY_TABLE');returned the same inforamtion except that INST_ID is different.
2) Does the preallocation affects insert sql only? I guess other operation are free to use any extent. Correct?
3) We are using ASSM. So I am not supposed to be tuning FREELISTS AND FREELIST GROUPS. Correct?
DB: 10.2.0.4
OS: RHEL 5.3

Answer 1

Just checked the document again ([url http://download.oracle.com/docs/cd/B19306_01/server.102/b14200/clauses001.htm#g1053419]INSTANCE integer)
If you are using automatic segment-space management, then the INSTANCE parameter of the allocate_extent_clause may not reserve the newly allocated space for the specified instance, because automatic segment-space management does not maintain rigid affinity between extents and instances.(How come I missed this??)
So Oracle ignores the instance clause for ASSM tablespace. Preparing a test with MSSM tablespace...