[data from a 1.6 GHz Opteron]

PERFCTR INIT: vendor 2, family 15, model 5, stepping 1, clock 1590517 kHz
PERFCTR INIT: NITER == 64
PERFCTR INIT: loop overhead is 243 cycles
PERFCTR INIT: rdtsc cost is 8.8 cycles (810 total)
PERFCTR INIT: rdpmc cost is 9.1 cycles (826 total)
PERFCTR INIT: rdmsr (counter) cost is 50.9 cycles (3506 total)
PERFCTR INIT: rdmsr (evntsel) cost is 57.0 cycles (3894 total)
PERFCTR INIT: wrmsr (counter) cost is 68.9 cycles (4658 total)
PERFCTR INIT: wrmsr (evntsel) cost is 317.6 cycles (20572 total)
PERFCTR INIT: read cr4 cost is 6.8 cycles (683 total)
PERFCTR INIT: write cr4 cost is 66.0 cycles (4470 total)
PERFCTR INIT: write LVTPC cost is 23.4 cycles (1744 total)
PERFCTR INIT: sync_core cost is 162.0 cycles (10613 total)
perfctr: driver 2.7.4, cpu type AMD K7/K8 at 1590517 kHz