PAPI_num_events returns 7, but I cannot use more than 5

[danicha]

Hey guys!

My CPU (Xeon X5550) supports 7 counters, and I used papi_avail to get the list of all available non derived events. But I cannot start more than 5 counters.

For instance, I can use PAPI_TOT_INS, PAPI_TLB_DM, PAPI_TLB_IM, PAPI_L3_TCM, PAPI_L3_TCA. But if I add PAPI_RES_STL, I get PAPI_ECNFLCT (-8, Event exists, but cannot be counted due to counter resource limitations).

Can it be that the OS is using two slots? Or that there are some conflicting counters that I cannot use together?