[data from a 1.6 GHz Pentium 4 (Northwood)]

PERFCTR INIT: vendor 0, family 15, model 2, stepping 4, clock 1614414 kHz
PERFCTR INIT: NITER == 64
PERFCTR INIT: loop overhead is 228 cycles
PERFCTR INIT: rdtsc cost is 78.5 cycles (5252 total)
PERFCTR INIT: rdpmc cost is 141.7 cycles (9300 total)
PERFCTR INIT: rdmsr (counter) cost is 251.6 cycles (16336 total)
PERFCTR INIT: rdmsr (escr) cost is 166.6 cycles (10892 total)
PERFCTR INIT: wrmsr (counter) cost is 849.7 cycles (54612 total) 
PERFCTR INIT: wrmsr (escr) cost is 921.0 cycles (59176 total)
PERFCTR INIT: read cr4 cost is 5.1 cycles (556 total)
PERFCTR INIT: write cr4 cost is 253.2 cycles (16436 total)
PERFCTR INIT: rdpmc (fast) cost is 62.4 cycles (4224 total)
PERFCTR INIT: rdmsr (cccr) cost is 167.6 cycles (10956 total)
PERFCTR INIT: wrmsr (cccr) cost is 873.3 cycles (56120 total)
perfctr: driver 2.3.7, cpu type Intel Pentium 4 at 1614414 kHz