snb_get_count
is_valid[cpu] = !snb_get_count(num, &val, cpu);
snb_get_count(TSC, &tsc_at_measure_start, base_cpu);
snb_get_count(TSC, &tsc_at_measure_end, base_cpu);
is_valid[cpu] |= !snb_get_count(num, &val, cpu);