PC Power Management Guide

[Dashken]

Have you ever wondered what all those C-state, P-state, S-state terms mean? Sure, you know they are related to power management in your PC, but what exactly do they do?

The PC Power Management Guide is here to answer all your power management questions. If you want to know what those terms mean, this is the guide for you.

Link : PC Power Management Guide

[belikethat]

wow pretty hardcode stuff
nice guide

[charge-n-go]

You guys can shoot me questions here. I'll answer them whenever I am free.

Dashken, is it possible to update my conclusion with this link?
This is my main reference for this article:
http://www.acpi.info/DOWNLOADS/ACPIspec30b.pdf

Thanks dude.

[neverthar]

Congrats on your first chargey. Damned good job at that too

[LIQNIT]

Very intresting reading.
Congrats on your frst article .

[charge-n-go]

Thanks for the feedbacks guys

[jojo4u]

I do not agree about your view of C1E. You only see in the light of one core C0 and on core C1. But does plain C1 really contradicts FID/VID mangement?
I'd say it's an P-state management "light" and a subset of EIST. It's a binary P-state mangement with actions based on C-states whereas EIST actions are based on decisions of software driver. Indeed, EIST also works the same way when C1E is disabled in the BIOS.
C1E must be seen independently of EIST and there are CPUs by Intel which only have C1E but no EIST[1].

[1] http://processorfinder.intel.com/det...px?sSpec=SL9XL

Btw, the forum activation mails get caught by SA because of a mailformed line(_ instead +):
Date: Wed, 11 Jul 2007 02:00:22 _0800

[charge-n-go]

I do not agree about your view of C1E. You only see in the light of one core C0 and on core C1. But does plain C1 really contradicts FID/VID mangement?

This is not my view, but specification says so. C1 does not mentioned anything about FID/VID, but C1E does mentioned.
C1: execute HLT instruction and put the core into halt state.
C1E: execute HLT instruction, put the core into halt state and transition the core into lowest P-state.

I'd say it's an P-state management "light" and a subset of EIST. It's a binary P-state mangement with actions based on C-states whereas EIST actions are based on decisions of software driver.

No, P-state is a subset of C-state power management. It is an active power management, where C1 state is a processor sleep state power management. The main difference is, active state executes instructions while sleep states don't execute. Besides this, EIST is an Operating System PM decision.
If u read the article carefully, I've included it into the diagram in conclusion page:
C0 - active state, CPU is not sleeping. P-state PM resides here.
C1 - sleep state (halt)
C2 - sleep state (stop grant)
C3 - sleep state (deep sleep)
C4 - sleep state (deeper sleep) ......

Indeed, EIST also works the same way when C1E is disabled in the BIOS. C1E must be seen independently of EIST and there are CPUs by Intel which only have C1E but no EIST

Yes, A processor can have C1E without EIST, or EIST without C1E. In C1E, only a portion of EIST logic is enabled - it will go to maximum and minimum P-state only. Let's say a CPU has P0, P1, P2 and P3, it will only transition between P0 and P3 if there is C1E but no EIST supported, and this only occur when the CPU is in C1 state.

http://processorfinder.intel.com/det...px?sSpec=SL9XL

You are giving an example of single core processor. At 2.0GHz, the multiplier is 10x and during P-state, it only works at 2.0GHz even though the workload is very light, as it doesnt support EIST. However, when the CPU is doing nothing at all, HLT instruction will be executed automatically and go into C1E state, where the clock speed will go down to 1.2GHz once the C1 state is entered.

[The_YongGrand]

Cool guide! Sorry, couldn't resist the pun...

Hey, which kind of state do the C'n'Q and EIST are in? Also, how am I going to enable the SpeedStep in Vista with a computer equipped with Pentium Dual-Core?

[charge-n-go]

Originally Posted by The_YongGrand

Cool guide! Sorry, couldn't resist the pun...

Hey, which kind of state do the C'n'Q and EIST are in? Also, how am I going to enable the SpeedStep in Vista with a computer equipped with Pentium Dual-Core?

Thanks dude.

Alrite, here is your answer

EIST -
manages processor P-state in the C0 state only.

C1E -
manages processor P-state in C1 state, using the same logic circuit in EIST.

Cool and Quiet -
manages all the processor power management states, including P-states and C-states. So far it has up to C1E for desktop variant. I don't know how far the Turion's CnQ goes, but i guess it would be at least C2 and above.


I am not sure about Vista, you can try the Windows XP method - change the power scheme to max battery saving.