what is throttling?

what is throttling?

[Keld Jørn Simonsen]

Hi!

I have googled around for a couple of hours to find out precisely what
throttling means. I did it before and found some useful information, but
this time I did not find the relevant data.

I would like to find out, which state precisely that the CPU enters when
throttling. Maybe it is different from CPU to CPU. Specifically I would
like to know if the CPU is completely powered off, my recollection of
some information I have seen earlier is that this may be the case.

And where is throttling done in the kernel?

Best regards
Keld


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Re: what is throttling?

[Dominik Brodowski]

On Wed, Oct 06, 2004 at 11:04:08AM +0200, Keld Jørn Simonsen wrote:
> Hi!
> 
> I have googled around for a couple of hours to find out precisely what
> throttling means. I did it before and found some useful information, but
> this time I did not find the relevant data.
> 
> I would like to find out, which state precisely that the CPU enters when
> throttling. Maybe it is different from CPU to CPU. Specifically I would
> like to know if the CPU is completely powered off, my recollection of
> some information I have seen earlier is that this may be the case.
> 
> And where is throttling done in the kernel?

It's managed in the ACPI processor module. Specific, extensive documentation
will be added to the ACPI HOWTO soon.

	Dominik


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Re: what is throttling?

[Andi Kleen]

On Wed, Oct 06, 2004 at 11:04:08AM +0200, Keld J?rn Simonsen wrote:
> Hi!
> 
> I have googled around for a couple of hours to find out precisely what
> throttling means. I did it before and found some useful information, but
> this time I did not find the relevant data.
> 
> I would like to find out, which state precisely that the CPU enters when
> throttling. Maybe it is different from CPU to CPU. Specifically I would
> like to know if the CPU is completely powered off, my recollection of
> some information I have seen earlier is that this may be the case.

On Intel CPUs Throttling means that the CPU skips each other
(or more) clock. This is quite slow, but only done to get 
the temperature down.

AMD CPUs don't have it afaik.

-Andi


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Re: what is throttling?

[Ville Syrjälä]

On Wed, Oct 06, 2004 at 01:49:35PM +0200, Andi Kleen wrote:
> On Wed, Oct 06, 2004 at 11:04:08AM +0200, Keld J?rn Simonsen wrote:
> > Hi!
> > 
> > I have googled around for a couple of hours to find out precisely what
> > throttling means. I did it before and found some useful information, but
> > this time I did not find the relevant data.
> > 
> > I would like to find out, which state precisely that the CPU enters when
> > throttling. Maybe it is different from CPU to CPU. Specifically I would
> > like to know if the CPU is completely powered off, my recollection of
> > some information I have seen earlier is that this may be the case.
> 
> On Intel CPUs Throttling means that the CPU skips each other
> (or more) clock. This is quite slow, but only done to get 
> the temperature down.
> 
> AMD CPUs don't have it afaik.

My AMD system (Duron 1300 + Abit KT7) can be throttled by 50%. In reality 
it feels more like 90% since even a temperature/fan monitor applet eats 
15% of my CPU when throttled. I haven't seen any benefits from throttling 
though.

-- 
Ville Syrjälä
syrjala-ORSVBvAovxo@public.gmane.org
http://www.sci.fi/~syrjala/


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Re: what is throttling?

[Bruno Ducrot]

On Wed, Oct 06, 2004 at 01:49:35PM +0200, Andi Kleen wrote:
> AMD CPUs don't have it afaik.

ducrot@poupoune:~$ cat /proc/acpi/processor/CPU1/throttling 
state count:             8
active state:            T0
states:
   *T0:                  00%
    T1:                  12%
    T2:                  25%
    T3:                  37%
    T4:                  50%
    T5:                  62%
    T6:                  75%
    T7:                  87%
ducrot@poupoune:~$ uname -m
x86_64

though I don't see real usefullness for throttling anyway, so
I've not tested if that works.

Cheers,

-- 
Bruno Ducrot

--  Which is worse:  ignorance or apathy?
--  Don't know.  Don't care.


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Re: what is throttling?

[Andi Kleen]

On Wed, Oct 06, 2004 at 04:12:45PM +0200, Bruno Ducrot wrote:
> On Wed, Oct 06, 2004 at 01:49:35PM +0200, Andi Kleen wrote:
> > AMD CPUs don't have it afaik.
> 
> ducrot@poupoune:~$ cat /proc/acpi/processor/CPU1/throttling 
> state count:             8
> active state:            T0
> states:
>    *T0:                  00%
>     T1:                  12%
>     T2:                  25%
>     T3:                  37%
>     T4:                  50%
>     T5:                  62%
>     T6:                  75%
>     T7:                  87%
> 
> though I don't see real usefullness for throttling anyway, so
> I've not tested if that works.

Indeed. It seems to work different from the Intel implementation
though, it doesn't skip clocks.

It's only useful to prevent your machine from melting when the 
fan fails or someone misdesigns the cooling setup.

-Andi


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Re: what is throttling?

[Bruno Ducrot]

On Wed, Oct 06, 2004 at 04:23:58PM +0200, Andi Kleen wrote:
> It's only useful to prevent your machine from melting when the 
> fan fails or someone misdesigns the cooling setup.
> 

Indeed, but I forgot to say that machine will use powernow-k8
in that case.

-- 
Bruno Ducrot

--  Which is worse:  ignorance or apathy?
--  Don't know.  Don't care.


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Re: what is throttling?

[Dominik Brodowski]

On Thu, Oct 07, 2004 at 02:54:07PM +0000, Anil Mamede wrote:
> Bruno Ducrot wrote:
> 
> 
> >though I don't see real usefullness for throttling anyway, so
> >I've not tested if that works.
> >
> 
> If throttling can save energy, why not throttling. The few things i do 
> with my computer is coding, doing some word process and listen to mp3. 
> Right now i cant put ACPI working. But if i had i whould throttle 
> because the CPU stays a lot of time idle.

If the CPU is in an idle mode of type C2, throttling doesn't reduce the
energy take-in of the CPU.

	Dominik


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Re: what is throttling?

[Dominik Brodowski]

On Thu, Oct 07, 2004 at 03:38:35PM +0000, Anil Mamede wrote:
> >If the CPU is in an idle mode of type C2, throttling doesn't reduce the
> >energy take-in of the CPU.
> 
> The CPU change modes automatically?

Not the CPU, the ACPI processor module automatically changes CPU power 
states (working / C1 / C2 / C3) if these are supported.

	Dominik


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Re: what is throttling?

[Anil Mamede]

Bruno Ducrot wrote:


> though I don't see real usefullness for throttling anyway, so
> I've not tested if that works.
> 

If throttling can save energy, why not throttling. The few things i do 
with my computer is coding, doing some word process and listen to mp3. 
Right now i cant put ACPI working. But if i had i whould throttle 
because the CPU stays a lot of time idle.

Anil Mamede



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Re: what is throttling?

[Andi Kleen]

On Thu, Oct 07, 2004 at 02:54:07PM +0000, Anil Mamede wrote:
> Bruno Ducrot wrote:
> 
> 
> >though I don't see real usefullness for throttling anyway, so
> >I've not tested if that works.
> >
> 
> If throttling can save energy, why not throttling. The few things i do 
> with my computer is coding, doing some word process and listen to mp3. 
> Right now i cant put ACPI working. But if i had i whould throttle 
> because the CPU stays a lot of time idle.

You don't really want throttling, it takes a long time to get out of
and is quite slow.  Result is that the desktop becomes very 
unresponsive.


-Andi


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Re: what is throttling?

[Anil Mamede]

Dominik Brodowski wrote:


> 
> 
> If the CPU is in an idle mode of type C2, throttling doesn't reduce the
> energy take-in of the CPU.

The CPU change modes automatically?

Anil Mamede



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