Renato,
When I tried running "opcontrol --start" (after 
  previously running "opcontrol --start-daemon") in dom0, I get this error 
  message:
/usr/local/bin/opcontrol: line 1639: echo: write error: 
  Operation not permitted
and this message in the Xen 
  console:
(XEN) xenoprof: operation 9 failed for dom 0 (status : 
  -1)
It looks like opcontrol is trying to do this: echo 1 > 
  /dev/oprofile/enable
and it is failing. "operation 9" maps to 
  XENOPROF_start which is consistent with running "opcontrol --start." At first, 
  I ignored the error because it gave the indication "Profiler running" but 
  after I ran "opcontrol --shutdown" followed by "opreport" in dom0, I got this 
  error message:
error: no sample files found: profile specification too 
  strict ?
Do you know why the write error is occurring? I followed the 
  steps in xenoprof_tutorial.ppt.
Dante