Likwid is a simple to install and use toolsuite of command line applications
for performance oriented programmers. It works for Intel and AMD processors
on the Linux operating system.

It consists of:

likwid-topology  - print thread and cache topology
likwid-features  - view and toggle feature reagister on Intel processors
likwid-perfCtr   - configure and read out hardware performance counters on Intel and AMD processors
likwid-pin       - pin your threaded application (pthread, Intel and gcc OpenMP to dedicated processors

For a detailed  documentation on the usage of the tools have a look at the
likwid wiki pages at:

http://code.google.com/p/likwid/wiki/Introduction

Known problems:

For likwid-perfCtr you need to load the msr kernel module. You have to be root to do so.

> modprobe msr

or with sudo

>sudo modprobe msr

Now there are new device files located in /dev/cpu/*/ for every core. In order
to use likwid-perfCtr as normal user you have to set appropriate read and write access
permissions on these device files. This can be done (as root or with sudo) with

>chmod o+rw /dev/cpu/*/msr

If you install likwid on a multi user system you may wish stricter access control
for accessing these device files. A common solution used on many other device files,
e.g. for audio, is to introduce a group and make a chown on the msr device files to
that group. Now if you execute likwid-perfCtr with setgid on that group the executing
user can use the tool but cannot directly write or read the msr device files.

Of course there are other solutions to this. For a single user private computer you can
savely use above change on the read and write permissions. It is recommended to put 
these commands in a startup script, so that it is automatically executed on every start.

If you have still problems with this or want to suggest a better solution
please let me know on the likwid mailing list:

http://groups.google.com/group/likwid-users