Question about cpufreq governors

Question about cpufreq governors

[DervishD]

    Hi all :)

    I have an AMD Athlon64, and according to "powernow-k8", it has to
fid's, for 1000MHz and 1800MHz. I don't know if this is correct or if I
should enable ACPI to have more fid's, but my question is not about
this.

    What I want to know is if I can choose "ondemand" governor instead
of the recommended for AMD64, namely the "conservative" governor, since
I will be switching between those two frequencies. I haven't found any
information about my CPU regarding latency when switching between
frequencies, so I don't know if I will be gaining anything using the
"conservative" governor.

    Which governor is better suited for a CPU with only two fid's,
"ondemand" or "conservative"?

    Thanks a lot in advance :)

    Raúl Núñez de Arenas Coronado

-- 
Linux Registered User 88736 | http://www.dervishd.net
It's my PC and I'll cry if I want to... RAmen!

Re: Question about cpufreq governors

[Jan Engelhardt]

On Jul 6 2007 22:50, DervishD wrote:
>
>    What I want to know is if I can choose "ondemand" governor instead
>of the recommended for AMD64, namely the "conservative" governor, since
>I will be switching between those two frequencies. I haven't found any
>information about my CPU regarding latency when switching between
>frequencies, so I don't know if I will be gaining anything using the
>"conservative" governor.
>
>    Which governor is better suited for a CPU with only two fid's,
>"ondemand" or "conservative"?

Depends on what you want. ondemand instantly switches when there is
something/nothing to do, while conservative uses a threshold (modeled upon
latency).


	Jan
-- 

Re: Question about cpufreq governors

[Arjan van de Ven]

On Fri, 2007-07-06 at 23:54 +0200, Jan Engelhardt wrote:
> On Jul 6 2007 22:50, DervishD wrote:
> >
> >    What I want to know is if I can choose "ondemand" governor instead
> >of the recommended for AMD64, namely the "conservative" governor, since
> >I will be switching between those two frequencies. I haven't found any
> >information about my CPU regarding latency when switching between
> >frequencies, so I don't know if I will be gaining anything using the
> >"conservative" governor.
> >
> >    Which governor is better suited for a CPU with only two fid's,
> >"ondemand" or "conservative"?
> 
> Depends on what you want. ondemand instantly switches when there is
> something/nothing to do, while conservative uses a threshold (modeled upon
> latency).

for power saving, the ondemand behavior is better in general. However if
you have a cpu that switches frequency very slowly, you may be better to
not go as high quickly because going back down is then burning more
power than needed potentially...

Re: Question about cpufreq governors

[DervishD]

    Hi Arjan :)

 * Arjan van de Ven <arjan@infradead.org> dixit:
> On Fri, 2007-07-06 at 23:54 +0200, Jan Engelhardt wrote:
> > On Jul 6 2007 22:50, DervishD wrote:
> > >
> > >    What I want to know is if I can choose "ondemand" governor instead
> > >of the recommended for AMD64, namely the "conservative" governor, since
> > >I will be switching between those two frequencies. I haven't found any
> > >information about my CPU regarding latency when switching between
> > >frequencies, so I don't know if I will be gaining anything using the
> > >"conservative" governor.
> > >
> > >    Which governor is better suited for a CPU with only two fid's,
> > >"ondemand" or "conservative"?
> > 
> > Depends on what you want. ondemand instantly switches when there is
> > something/nothing to do, while conservative uses a threshold (modeled upon
> > latency).
> 
> for power saving, the ondemand behavior is better in general. However if
> you have a cpu that switches frequency very slowly, you may be better to
> not go as high quickly because going back down is then burning more
> power than needed potentially...

    That's the problem: I want to use "ondemand" but I don't know if it
will work properly with my CPU because I don't know if my CPU switches
frequency fast or slow :( I can find that information, although the
Kconfig file for cpufreq says that AMD64 has latency problems (but I can
confirm that, I'm afraid).

    Thanks for your answer :)

    Raúl Núñez de Arenas Coronado

-- 
Linux Registered User 88736 | http://www.dervishd.net
It's my PC and I'll cry if I want to... RAmen!

Re: Question about cpufreq governors

[DervishD]

    Hi Jan :)

 * Jan Engelhardt <jengelh@computergmbh.de> dixit:
> On Jul 6 2007 22:50, DervishD wrote:
> >
> >    What I want to know is if I can choose "ondemand" governor instead
> >of the recommended for AMD64, namely the "conservative" governor, since
> >I will be switching between those two frequencies. I haven't found any
> >information about my CPU regarding latency when switching between
> >frequencies, so I don't know if I will be gaining anything using the
> >"conservative" governor.
> >
> >    Which governor is better suited for a CPU with only two fid's,
> >"ondemand" or "conservative"?
> 
> Depends on what you want. ondemand instantly switches when there is
> something/nothing to do, while conservative uses a threshold (modeled upon
> latency).

    Yes, I know the difference, I'm afraid I didn't ask my question
correctly O:). What I meant is that, since I don't know if my CPU has
latency problems when switching from "slow" freq to "fast" freq, if I
can use "ondemand" safely or if I must use "conservative" due to latency
problems with my CPU.

    Thanks for your answer :)

    Raúl Núñez de Arenas Coronado

-- 
Linux Registered User 88736 | http://www.dervishd.net
It's my PC and I'll cry if I want to... RAmen!