There is a new release my x86 performance-monitoring counters
patch for Linux. From the README:

Latest Updates
--------------
1999-11-14
- Version 0.8 with support for Linux kernels 2.3.28 and 2.2.13.
- Major updates to reduce the overhead of maintaining virtual
  performance-monitoring counters:
    - The control registers are cached and updated lazily.
    - The counter registers are no longer written to.
    - Unused counters are no longer manipulated at all.
      (This matters especially for the AMD K7.)
- Reduced the process scheduling overhead for processes not
  using performance-monitoring counters.
- Minor code cleanups and bug fixes, and documentation updates.

This and future versions of this package can be downloaded from
http://www.csd.uu.se/~mikpe/linux/perfctr/

I plan to support counter overflow interrupts via the local APIC
in the next release. Programming the APIC isn't difficult, but
it's not yet clear what the API for this feature should be, and
more kernel patches will be needed for enabling APIC access on
UP machines. (I already have preliminary code which does this.)


/ Mikael Pettersson