linux - oprofile can not use hardware performance counters

I have debian 5.0 linux server on an IBM HS22 blade with 2 Xeon E5504 processors. I found out that oprofile could not recognize hardware performance counters on this setup, only timer interrupt is available:

# opcontrol -l
Using timer interrupt.
# cat /dev/oprofile/cpu_type 
timer

System information is:

# cat /etc/issue.net 
Debian GNU/Linux 5.0
# uname -a
Linux xxx 2.6.26-2-686-bigmem #1 SMP Mon Jun 21 06:45:17 UTC 2010 i686 GNU/Linux

oprofile was installed from debian repository using apt.

# opcontrol --version
opcontrol: oprofile 0.9.3 compiled on Feb 10 2008 12:08:26

What should I do to enable hardware performance counters? Thanks!