Intel clock unhalted monitor event

CPU_CLK_UNHALTED.THREAD
Description:
 Counts the number of thread cycles while the thread is not in a halt state. The thread enters the halt state when it is running the HLT instruction. The thread frequency may change from time to time due to thermal or power throttling.

cpu_clk_unhalted.rdtsc
 This event counts reference clock cycles while the clock signal on the core is running. The reference clock operates at a fixed frequency, irrespective of core frequency changes due to performance state transitions. Processors may implement this behavior differently.

我自己在nehalem 上测了一下，
thread 会有变化

rdtsc 很稳定，但是频率比thread 低 2倍左右。