ACPI各种状态非常有用.docxVIP

C States就是CPU的 idle的 states，包括C0，C1，C2，C3，C4。。。。P States就是CPU在C0状态下，使用特定CPU的降频降压功能来省电（不同的CPU厂商的方式不同），主要表现就是CPU的频率在变化T States就是CPU的Throttling，也就是在一定的频率下，可以让cpu在一段时间工作，一段时间不工作，也就是存在一个Duty cycle，这块和南桥的PMU有关系。问题1）T States是不是 P states？ 十有八九都不是，但是还想问问各位，确定一下。声明在intel的资料中看到的P states概念，在MS文档中看到的是T states名词。问题2）FADT的DUTY_OFFSET和DUTY_WIDTH到底应该指的是什么？为什么两者加起来必须大于4？问题3）FADT中的PSTATE_CNT和CST_CNT到底指的什么？PSTATE_CNT就是P_CNT吗？谁有空给回答一下，呵呵 回答1： C-State是CPU State, 基本上CPU和停止運行. P State則是降頻和降電壓. CPU還是會繼續跑Code. T-State則是CPU根據系統溫度, 跑一下, 停一下來降低熱度. 回答2： P-States are OS controllable, (based as well on peformance profile). While C-States only change when CPU is idle, P-States changes during execution.?T-States are a sort of P-State, as it changes during execution, they can be OS controllable but often also HW-controllable. They are mostly used during thermal events on the CPU (overheat etc.). P-States change voltage and frequency parameters, but T-States stops the CPU for brief moments. The uses and when to go to a certain state is based on (user or powerdevice controlled) power profiles, latency and device interaction etc. 回答3： T-States (Processor Throttling States)T-states refer to throttling the processor clock to lower frequencies in order to reduce thermal effects. This means that the CPU is forced to be idle a fixed percentage of its cycles per second. Throttling states range from T1 (the CPU has no forced idle cycles) to Tn, with the percentage of idle cycles increasing the greater n is.Note that throttling does not reduce voltage and since the CPU is forced to idle part of the time, processes will take longer to finish and will consume more power instead of saving any power.T-states are only useful if reducing thermal effects is the primary goal. Since T-states can interfere with C-states (preventing the CPU from reaching higher C-states), they can even increase power consumption in a modern CPU capable of C-states.