[data from a 1.7GHz Pentium 4 (Willamette)]

PERFCTR INIT: vendor 0, family 15, model 1, stepping 2, clock 1707591 kHz
PERFCTR INIT: NITER == 64
PERFCTR INIT: loop overhead is 208 cycles
PERFCTR INIT: rdtsc cost is 78.2 cycles (5216 total)
PERFCTR INIT: rdpmc cost is 145.6 cycles (9532 total)
PERFCTR INIT: rdmsr (counter) cost is 247.9 cycles (16076 total)
PERFCTR INIT: rdmsr (escr) cost is 163.0 cycles (10644 total)
PERFCTR INIT: wrmsr (counter) cost is 819.2 cycles (52640 total)
PERFCTR INIT: wrmsr (escr) cost is 877.5 cycles (56372 total)
PERFCTR INIT: read cr4 cost is 5.3 cycles (548 total)
PERFCTR INIT: write cr4 cost is 245.7 cycles (15936 total)
PERFCTR INIT: rdpmc (fast) cost is 60.1 cycles (4060 total)
PERFCTR INIT: rdmsr (cccr) cost is 163.9 cycles (10700 total)
PERFCTR INIT: wrmsr (cccr) cost is 834.0 cycles (53584 total)
perfctr: driver 2.3.3, cpu type Intel Pentium 4 at 1707591 kHz