[data from a 1.3GHz Pentium-M]

PERFCTR INIT: vendor 0, family 6, model 9, stepping 5, clock 1300408 kHz
PERFCTR INIT: NITER == 64
PERFCTR INIT: loop overhead is 282 cycles
PERFCTR INIT: rdtsc cost is 47.6 cycles (3330 total)
PERFCTR INIT: rdpmc cost is 43.3 cycles (3054 total)
PERFCTR INIT: rdmsr (counter) cost is 95.0 cycles (6368 total)
PERFCTR INIT: rdmsr (evntsel) cost is 80.8 cycles (5455 total)
PERFCTR INIT: wrmsr (counter) cost is 143.4 cycles (9462 total)
PERFCTR INIT: wrmsr (evntsel) cost is 132.0 cycles (8735 total)
PERFCTR INIT: read cr4 cost is 2.8 cycles (465 total)
PERFCTR INIT: write cr4 cost is 49.7 cycles (3465 total)
PERFCTR INIT: sync_core cost is 140.7 cycles (9291 total)

on ac-power

PERFCTR INIT: vendor 0, family 6, model 9, stepping 5, clock 1300434 kHz
PERFCTR INIT: NITER == 64
PERFCTR INIT: loop overhead is 113 cycles
PERFCTR INIT: rdtsc cost is 50.0 cycles (3319 total)
PERFCTR INIT: rdpmc cost is 41.2 cycles (2750 total)
PERFCTR INIT: rdmsr (counter) cost is 95.3 cycles (6215 total)
PERFCTR INIT: rdmsr (evntsel) cost is 81.1 cycles (5304 total)
PERFCTR INIT: wrmsr (counter) cost is 143.7 cycles (9313 total)
PERFCTR INIT: wrmsr (evntsel) cost is 132.3 cycles (8584 total)
PERFCTR INIT: read cr4 cost is 2.8 cycles (294 total)
PERFCTR INIT: write cr4 cost is 49.9 cycles (3311 total)
PERFCTR INIT: write LVTPC cost is 9.4 cycles (718 total)
perfctr: driver 2.7.3, cpu type Intel P6 at 1300434 kHz

on battery:

PERFCTR INIT: vendor 0, family 6, model 9, stepping 5, clock 600199 kHz
PERFCTR INIT: NITER == 64
PERFCTR INIT: loop overhead is 113 cycles
PERFCTR INIT: rdtsc cost is 47.3 cycles (3146 total)
PERFCTR INIT: rdpmc cost is 41.2 cycles (2750 total)
PERFCTR INIT: rdmsr (counter) cost is 95.3 cycles (6215 total)
PERFCTR INIT: rdmsr (evntsel) cost is 81.1 cycles (5304 total)
PERFCTR INIT: wrmsr (counter) cost is 143.7 cycles (9313 total)
PERFCTR INIT: wrmsr (evntsel) cost is 132.3 cycles (8584 total)
PERFCTR INIT: read cr4 cost is 2.8 cycles (294 total)
PERFCTR INIT: write cr4 cost is 49.9 cycles (3311 total)
PERFCTR INIT: write LVTPC cost is 8.4 cycles (652 total)
perfctr: driver 2.7.3, cpu type Intel P6 at 600199 kHz