I have some doubts regarding cpufreq for SMP systems (for developing
http://mnm.uib.es/~gallir/cpudyn/).
If I remember well, I read a while ago that cpufreq didn't work in SMP
systems, but reading the docs and kernel/cpufreq.c, it seems there should be
any problem?
Is it true?
OTH, I trying it on a P4 HT, and it works, changes in the frequency of one of
the "cpu's", changes both.
What happens in the case of several real cpu's? Does it keep the same
frequency for every cpu? According to a comment in cpufreq.c, it seems that
each cpu might have different frequencies.
So, what's recommended? Change the frequency of every cpu one by one?
Thanks,
PS: sorry, I don't have any cpufreq/SMP machine at hand.
--
ricardo galli GPG id C8114D34
http://mnm.uib.es/~gallir/
On Thu, 31 Jul 2003 23:53:54 +0200, Ricardo Galli wrote:
> I have some doubts regarding cpufreq for SMP systems (for developing
> http://mnm.uib.es/~gallir/cpudyn/).
>
> If I remember well, I read a while ago that cpufreq didn't work in SMP
> systems, but reading the docs and kernel/cpufreq.c, it seems there should be
> any problem?
>
> Is it true?
>
> OTH, I trying it on a P4 HT, and it works, changes in the frequency of one of
> the "cpu's", changes both.
That makes sense, since the CPU only has one clock.
> What happens in the case of several real cpu's? Does it keep the same
> frequency for every cpu? According to a comment in cpufreq.c, it seems that
> each cpu might have different frequencies.
AFAIK no SMP systems have voltage/frequency scaling (SpeedStep/PowerNow).
I've heard that ACPI P-states works on SMP, but if it's not doing
voltage/frequency scaling then I don't know what it's doing.
Wes Felter - [email protected] - http://felter.org/wesley/
Le sam 02/08/2003 ? 00:36, Wes Felter a ?crit :
> AFAIK no SMP systems have voltage/frequency scaling (SpeedStep/PowerNow).
> I've heard that ACPI P-states works on SMP, but if it's not doing
> voltage/frequency scaling then I don't know what it's doing.
I've got an ABit VP6 (VIA686, dual P3), and the processors speed and
voltage can be set in the BIOS. Does it count ?
Xav
On Fri, 2003-08-01 at 17:51, Xavier Bestel wrote:
> Le sam 02/08/2003 ? 00:36, Wes Felter a ?crit :
> > AFAIK no SMP systems have voltage/frequency scaling (SpeedStep/PowerNow).
> > I've heard that ACPI P-states works on SMP, but if it's not doing
> > voltage/frequency scaling then I don't know what it's doing.
>
> I've got an ABit VP6 (VIA686, dual P3), and the processors speed and
> voltage can be set in the BIOS. Does it count ?
I meant dynamic voltage/frequency scaling, so that doesn't count.
Wes Felter - [email protected] - http://felter.org/wesley/
Hi!
> > > AFAIK no SMP systems have voltage/frequency scaling (SpeedStep/PowerNow).
> > > I've heard that ACPI P-states works on SMP, but if it's not doing
> > > voltage/frequency scaling then I don't know what it's doing.
> >
> > I've got an ABit VP6 (VIA686, dual P3), and the processors speed and
> > voltage can be set in the BIOS. Does it count ?
>
> I meant dynamic voltage/frequency scaling, so that doesn't count.
If his bios can change voltage/frequency, kernel can probably do the
same. So his hardware probably can be supported by cpufreq.
Pavel
--
When do you have a heart between your knees?
[Johanka's followup: and *two* hearts?]
On Tue, Aug 05, 2003 at 01:16:47PM +0200, Pavel Machek wrote:
> Hi!
>
> > > > AFAIK no SMP systems have voltage/frequency scaling (SpeedStep/PowerNow).
> > > > I've heard that ACPI P-states works on SMP, but if it's not doing
> > > > voltage/frequency scaling then I don't know what it's doing.
> > >
> > > I've got an ABit VP6 (VIA686, dual P3), and the processors speed and
> > > voltage can be set in the BIOS. Does it count ?
> >
> > I meant dynamic voltage/frequency scaling, so that doesn't count.
>
> If his bios can change voltage/frequency, kernel can probably do the
> same. So his hardware probably can be supported by cpufreq.
The cpufreq core supports SMP. But only a few SMP capable CPUs offer cpu
frequency and/or voltage scaling. Those who do (e.g. P4/Xeon, UltraSparc
variants, and some ARM processors, IIRC) are well supported by cpufreq.
Dominik