ACPI C and P states on Conroe

ACPI C and P states on Conroe

[Joe Harvell]

I am trying to enable all the power saving features I can on my Conroe
E6600.  After much searching on the web, I am a little confused about
the Linux kernel support for ACPI on the Conroe.

Here is my setup:
Intel Core2 Duo E6600
Asus P5-B Deluxe board (Intel P965).
I am running a Gentoo kernel based on 2.6.19.4.

I have managed to enable EIST using cpufreq with the speedstep-centrino
driver.  But my understanding from browsing the ACPI spec is that this
is still within C0, i.e. not much power savings.

Here are my questions:

1) For P states, which cpufreq driver should I be using?  I've heard
speedstep-centrino is deprecated (but only some aspects of it) that are
being moved into acpi-cpufreq.  But I can't get acpi-cpufreq to load in
my kernel version.  Also, I would have thought speedstep-ich would be
the driver, just based on the name.  How do I know (other than trying
all modules to see which one loads) which one I should be using?
2) What kind of support for C1-C3 does the Conroe have?  The ACPI spec
says C2 and C3 require chipset support on the motherboard.  Does P965
have that.  Does it matter between boards (e.g. P5B)?
3) What versions of the kernel support C1-C3 states?  What kernel
options are germane to this?  What libraries/tools are involved?

---
Joe Harvell

Re: ACPI C and P states on Conroe

[Len Brown]

On Tuesday 30 January 2007 12:35, Joe Harvell wrote:
> I am trying to enable all the power saving features I can on my Conroe
> E6600.  After much searching on the web, I am a little confused about
> the Linux kernel support for ACPI on the Conroe.
> 
> Here is my setup:
> Intel Core2 Duo E6600
> Asus P5-B Deluxe board (Intel P965).
> I am running a Gentoo kernel based on 2.6.19.4.
> 
> I have managed to enable EIST using cpufreq with the speedstep-centrino
> driver.  But my understanding from browsing the ACPI spec is that this
> is still within C0, i.e. not much power savings.

Right, P-states are effective only when code is executing,
and on this processor (with C1E) will have no effect on idle power.

> Here are my questions:
> 
> 1) For P states, which cpufreq driver should I be using?  I've heard
> speedstep-centrino is deprecated (but only some aspects of it) that are
> being moved into acpi-cpufreq.  But I can't get acpi-cpufreq to load in
> my kernel version.

In 2.6.19 I believe that speedstep-centrino is the one to use.
The transition to acpi-cpufreq happens in 2.6.20.

> Also, I would have thought speedstep-ich would be 
> the driver, just based on the name.

Don't use speedstep-ich.

> How do I know (other than trying 
> all modules to see which one loads) which one I should be using?
> 2) What kind of support for C1-C3 does the Conroe have?  The ACPI spec
> says C2 and C3 require chipset support on the motherboard.  Does P965
> have that.  Does it matter between boards (e.g. P5B)?

I believe that Conroe currently supports just C1 --
this is true for the ones I have.

Internally it is an "Enhanced C1" called C1E where the voltage is reduced
in C1-- but this is transparent to software, which thinks it is just C1.

You can observe this in
/proc/acpi/processor/*/power

> 3) What versions of the kernel support C1-C3 states?  What kernel
> options are germane to this?  What libraries/tools are involved?

C1-C3 have been supported for a long time.
2.6.20 adds a few tweaks to use a more efficient implementation,
but you'll not notice a difference on today's desktop processor.

cheers,
-Len

Re: ACPI C and P states on Conroe

[Robert Hancock]

Joe Harvell wrote:
> I am trying to enable all the power saving features I can on my Conroe 
> E6600.  After much searching on the web, I am a little confused about 
> the Linux kernel support for ACPI on the Conroe.
> 
> Here is my setup:
> Intel Core2 Duo E6600
> Asus P5-B Deluxe board (Intel P965).
> I am running a Gentoo kernel based on 2.6.19.4.
> 
> I have managed to enable EIST using cpufreq with the speedstep-centrino 
> driver.  But my understanding from browsing the ACPI spec is that this 
> is still within C0, i.e. not much power savings.

C-states are something else entirely, frequency scaling and C-states are 
essentially independent. You can be in lower frequency and C1, C2, etc. 
and it will still use less power.

> 
> Here are my questions:
> 
> 1) For P states, which cpufreq driver should I be using?  I've heard 
> speedstep-centrino is deprecated (but only some aspects of it) that are 

Right.

> being moved into acpi-cpufreq.  But I can't get acpi-cpufreq to load in 
> my kernel version.  Also, I would have thought speedstep-ich would be 

Are you sure? Are you getting error messages?

> the driver, just based on the name.  How do I know (other than trying 

No, that's only for some older chipsets.

> all modules to see which one loads) which one I should be using?

That's the easiest way, and that's what Fedora does for example (just 
compile all the drivers into the kernel). acpi-cpufreq should be the one 
for all modern boards, however.

> 2) What kind of support for C1-C3 does the Conroe have?  The ACPI spec 
> says C2 and C3 require chipset support on the motherboard.  Does P965 
> have that.  Does it matter between boards (e.g. P5B)?

The kernel will only use C2 and C3 if the motherboard exports support 
for it through ACPI. Most desktop boards don't, this is normally only 
found on laptops.

-- 
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@nospamshaw.ca
Home Page: http://www.roberthancock.com/

Re: ACPI C and P states on Conroe

[Joe Harvell]

Robert Hancock wrote:
> Joe Harvell wrote:
>
>>
>> Here are my questions:
>>
>> 1) For P states, which cpufreq driver should I be using?  I've heard 
>> speedstep-centrino is deprecated (but only some aspects of it) that are 
>
> Right.
>
>> being moved into acpi-cpufreq.  But I can't get acpi-cpufreq to load 
>> in my kernel version.  Also, I would have thought speedstep-ich would be 
>
> Are you sure? Are you getting error messages?
>
>
I forget what the output from modprobe said.  But I had 
cpufreq.debug=7.  Here are the logs:

Jan 29 09:10:38 [kernel] acpi-cpufreq: acpi_cpufreq_init
Jan 29 09:10:38 [kernel] acpi-cpufreq: acpi_cpufreq_early_init
Jan 29 09:10:38 [kernel] cpufreq-core: trying to register driver 
acpi-cpufreq
Jan 29 09:10:38 [kernel] cpufreq-core: adding CPU 0
Jan 29 09:10:38 [kernel] acpi-cpufreq: acpi_cpufreq_cpu_init
Jan 29 09:10:38 [kernel] acpi-cpufreq: Unsupported address space [127, 127]
Jan 29 09:10:38 [kernel] cpufreq-core: initialization failed
Jan 29 09:10:38 [kernel] cpufreq-core: adding CPU 1
Jan 29 09:10:38 [kernel] acpi-cpufreq: acpi_cpufreq_cpu_init
Jan 29 09:10:38 [kernel] acpi-cpufreq: Unsupported address space [127, 127]
Jan 29 09:10:38 [kernel] cpufreq-core: initialization failed
Jan 29 09:10:38 [kernel] cpufreq-core: no CPU initialized for driver 
acpi-cpufreq
Jan 29 09:10:38 [kernel] cpufreq-core: unregistering CPU 0
Jan 29 09:10:38 [kernel] cpufreq-core: unregistering CPU 1

>
>> 2) What kind of support for C1-C3 does the Conroe have?  The ACPI 
>> spec says C2 and C3 require chipset support on the motherboard.  Does 
>> P965 have that.  Does it matter between boards (e.g. P5B)?
>
> The kernel will only use C2 and C3 if the motherboard exports support 
> for it through ACPI. Most desktop boards don't, this is normally only 
> found on laptops.
>
Okay.  I understand the distinction between what the processor supports 
and what the motherboard exports via the ACPI tables.  I do still want 
to know what C states the E6600 supports.  Does anyone know?  Also, I've 
heard the it's possible to modify the DSDT on boards to add interfaces 
to processor features that the board does not provide.  Of course this 
is a dead end if E6600 doesn't support these low power states to begin 
with.  Assuming it does, does anyone know if it's possible to get them 
working on the Asus P5B Deluxe?

ACPI C and P states on Conroe

[Joe Harvell]

I am trying to enable all the power saving features I can on my Conroe 
E6600.  After much searching on the web, I am a little confused about 
the Linux kernel support for ACPI on the Conroe.

Here is my setup:
Intel Core2 Duo E6600
Asus P5-B Deluxe board (Intel P965).
I am running a Gentoo kernel based on 2.6.19.4.

I have managed to enable EIST using cpufreq with the speedstep-centrino 
driver.  But my understanding from browsing the ACPI spec is that this 
is still within C0, i.e. not much power savings.

Here are my questions:

1) For P states, which cpufreq driver should I be using?  I've heard 
speedstep-centrino is deprecated (but only some aspects of it) that are 
being moved into acpi-cpufreq.  But I can't get acpi-cpufreq to load in 
my kernel version.  Also, I would have thought speedstep-ich would be 
the driver, just based on the name.  How do I know (other than trying 
all modules to see which one loads) which one I should be using?
2) What kind of support for C1-C3 does the Conroe have?  The ACPI spec 
says C2 and C3 require chipset support on the motherboard.  Does P965 
have that.  Does it matter between boards (e.g. P5B)?
3) What versions of the kernel support C1-C3 states?  What kernel 
options are germane to this?  What libraries/tools are involved?

---
Joe Harvell

RE: ACPI C and P states on Conroe

[Pallipadi, Venkatesh]

C0 is the state when processor is executing instruction.
C1-C3 is the state that kernel puts the CPU into when there is nothing
to run (idle loop).
C1 is supported by all processors and it is entered either by using
"hlt" or "mwait" instructions. You don't have to do anything to enable
this. It should be getting used already (unless you are using
"idle=poll" in which case C1 will not be used).
C2 and C3 however are not supported on all processors/platforms
typically. If it is supported, BIOS will export these states information
to OS, through ACPI and kernel acpi processor module will enable those
states. As long as you have CONFIG_ACPI_PROCESSOR enabled, this support
will be built in and should get enabled (if your platform supports this
feature). There are no magic setup to enable this. If present, you will
see info about these C-states here - /proc/acpi/processor/CPU*/power

-Venki

>-----Original Message-----
>From: linux-kernel-owner@vger.kernel.org 
>[mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of Joe Harvell
>Sent: Tuesday, January 30, 2007 9:34 AM
>To: linux-kernel@vger.kernel.org
>Subject: ACPI C and P states on Conroe
>
>I am trying to enable all the power saving features I can on my Conroe 
>E6600.  After much searching on the web, I am a little confused about 
>the Linux kernel support for ACPI on the Conroe.
>
>Here is my setup:
>Intel Core2 Duo E6600
>Asus P5-B Deluxe board (Intel P965).
>I am running a Gentoo kernel based on 2.6.19.4.
>
>I have managed to enable EIST using cpufreq with the 
>speedstep-centrino 
>driver.  But my understanding from browsing the ACPI spec is that this 
>is still within C0, i.e. not much power savings.
>
>Here are my questions:
>
>1) For P states, which cpufreq driver should I be using?  I've heard 
>speedstep-centrino is deprecated (but only some aspects of it) 
>that are 
>being moved into acpi-cpufreq.  But I can't get acpi-cpufreq 
>to load in 
>my kernel version.  Also, I would have thought speedstep-ich would be 
>the driver, just based on the name.  How do I know (other than trying 
>all modules to see which one loads) which one I should be using?
>2) What kind of support for C1-C3 does the Conroe have?  The ACPI spec 
>says C2 and C3 require chipset support on the motherboard.  Does P965 
>have that.  Does it matter between boards (e.g. P5B)?
>3) What versions of the kernel support C1-C3 states?  What kernel 
>options are germane to this?  What libraries/tools are involved?
>
>---
>Joe Harvell
>-
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