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ACPI各种状态,非常有用


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.


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