SQL> @trace_waits

This script uses event 10046, level 8 to trace the event waits in
the top N sessions affected by waits for a particular resource.

Select sessions waiting for: buffer busy waits
Number of sessions to trace: 5
Seconds to leave tracing on: 900

Tracing ... Please wait ...

PL/SQL procedure successfully completed.
 
SQL> exit
$ cd udump
$ grep 'buffer busy waits' ora_*.trc |
> sed -e 's/.*p1=/  file /' -e 's/ p2=/  block /' -e 's/ p3.*//' |
> sort |
> uniq -c |
> sort -nr |
> head -5
  42    file 2    block 1036
  12    file 24   block 3
  10    file 2    block 1252
   7    file 2    block 112
   6    file 7    block 5122
$