I need to count L2 cache misses (my cpu is i5-3550), so I downloaded last PAPI version. I followed instructions contained in the archive to install it (./configure, make and make install) and it worked. The only problem is that it seems it cannot access performace monitoring counters,in fact in the INSTALL.txt it says: "Kernel needs some modifications to provide PAPI access to the performance monitoring counters." Is it really necessary? If so, can you guide me step by step?