is it really better speedstep-ich vs. p4-clockmod cpufreq driver?

is it really better speedstep-ich vs. p4-clockmod cpufreq driver?

[Riccardo Vestrini]

it seems that speedstep-ich and acpi cpufreq driver have only two usable
clock frequencies, while p4-clockmod has eight
my cpu is: Intel Mobile Intel(R) Pentium(R) 4   CPU 3.06GHz stepping 09



last 2.6 kernel I tried (2.6.7) has introduced a warning while loading
p4-clockmod module:

p4-clockmod: P4/Xeon(TM) CPU On-Demand Clock Modulation available
p4-clockmod: Warning: Pentium 4-M detected. The speedstep-ich or acpi
cpufreq modules offer voltage scaling in addition of frequency scaling.
You should use either one instead of p4-clockmod, if possible.

so I immediatly switched to speedstep-ich discovering that:
$ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
3066590 1599960

while with p4-clockmod I have:
$ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
383323 766647 1149971 1533295 1916618 2299942 2683266 3066590

using acpi driver gives a message:
cpufreq: CPU0 - ACPI performance management activated.
cpufreq:  P0: 3059 MHz, 24000 mW, 100 uS
cpufreq: *P1: 1596 MHz, 12000 mW, 100 uS
but:
$ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
3059000 1596000


i do not know what driver is supposed to be better and why speedstep-ich 
driver has only two frequencies

thank you

-- 

                                Riccardo Vestrini
                               <riccardov@sssup.it>

Re: is it really better speedstep-ich vs. p4-clockmod cpufreq driver?

[Rutger Nijlunsing]

On Fri, Jul 23, 2004 at 08:54:39PM +0200, Riccardo Vestrini wrote:
> it seems that speedstep-ich and acpi cpufreq driver have only two usable
> clock frequencies, while p4-clockmod has eight
> my cpu is: Intel Mobile Intel(R) Pentium(R) 4   CPU 3.06GHz stepping 09
> 
[snip]
> 
> i do not know what driver is supposed to be better and why speedstep-ich 
> driver has only two frequencies

p4-clockmod is not really a cpufreq driver: it does not change the
frequency. The only function is to have 'idle-cycles' to cool down the
processor during intensive CPU programs: this is what the processor
does when it gets too hot.

The speedstep driver _does_ change the frequency (and/or voltage) and
gives other advantages like less power consumption.

So use speedstep.

-- 
Rutger Nijlunsing ---------------------------- rutger ed tux tmfweb nl
never attribute to a conspiracy which can be explained by incompetence
----------------------------------------------------------------------

is it really better speedstep-ich vs. p4-clockmod cpufreq driver?

[Riccardo Vestrini]

it seems that speedstep-ich and acpi cpufreq driver have only two usable 
clock frequencies, while p4-clockmod has eight
my cpu is: Intel Mobile Intel(R) Pentium(R) 4   CPU 3.06GHz stepping 09



last 2.6 kernel I tried (2.6.7) has introduced a warning while loading 
p4-clockmod module:

p4-clockmod: P4/Xeon(TM) CPU On-Demand Clock Modulation available
p4-clockmod: Warning: Pentium 4-M detected. The speedstep-ich or acpi 
cpufreq modules offer voltage scaling in addition of frequency scaling. 
You should use either one instead of p4-clockmod, if possible.

so I immediatly switched to speedstep-ich discovering that:
$ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
3066590 1599960

while with p4-clockmod I have:
$ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
383323 766647 1149971 1533295 1916618 2299942 2683266 3066590

using acpi driver gives a message:
cpufreq: CPU0 - ACPI performance management activated.
cpufreq:  P0: 3059 MHz, 24000 mW, 100 uS
cpufreq: *P1: 1596 MHz, 12000 mW, 100 uS
but:
$ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
3059000 1596000


so, what driver is supposed to be better? and why speedstep-ich driver 
has only two frequencies?


-- 

                                Riccardo Vestrini
                               <riccardov@sssup.it>

"Computers are good at following instructions,
  but not at reading your mind." - D. E. Knuth, The TeXbook

Re: is it really better speedstep-ich vs. p4-clockmod cpufreq driver?

[Jim Carter]

On Thu, 22 Jul 2004, Riccardo Vestrini wrote:

> it seems that speedstep-ich and acpi cpufreq driver have only two usable clock
> frequencies, while p4-clockmod has eight
> my cpu is: Intel Mobile Intel(R) Pentium(R) 4   CPU 3.06GHz stepping 09

> p4-clockmod: P4/Xeon(TM) CPU On-Demand Clock Modulation available
> p4-clockmod: Warning: Pentium 4-M detected. The speedstep-ich or acpi cpufreq
> modules offer voltage scaling in addition of frequency scaling. You should use
> either one instead of p4-clockmod, if possible.
> 
> so, what driver is supposed to be better? and why speedstep-ich driver has
> only two frequencies?

The CPU on my laptop is a Pentium III-M (Coppermine) and so only 
speedstep-ich is useful for me.  However, I can shed some light on this 
issue.  My CPU frequencies are 733 MHz and 1000 MHz, but at the lower speed 
the CPU also runs at 3.3 volts, vs. 5 volts at high speed.  This means that 
the power consumption is about half at low speed (it's approximately speed 
times voltage), which is important for me when operating in the field on 
battery power.  Also, when running high speed I need to put a pillow on my 
lap and the machine on the pillow, because the bottom gets so hot.  (Yes, I 
make very sure that the pillow doesn't block the air ducts, and the fan 
does a good job of keeping the insides cool.  The CPU and graphics chip 
have a big heat-pipe running into the air duct.)

Definitely the voltage modulation is important to have.

Also as for strategies, if you have dynamic speed modulation, generally if
the CPU is busy less than 73% of the time, then my machine should be run at
the lowest speed, whereas if tasks are waiting to run then it should be put
in the highest speed.  In a typical workload it's very rare for the needed
throughput to be steadily between 73% and 100% so the intermediate speeds
could be useful; this is true even if the available speed range is greater.  
Actually, hardly anyone uses the full capacity of their CPU, and I don't
even bother to run the dynamic modulation daemon, just leaving it at low
speed all the time.  I switch manually if I have a big simulation to do.

Hope this helps.

James F. Carter          Voice 310 825 2897    FAX 310 206 6673
UCLA-Mathnet;  6115 MSA; 405 Hilgard Ave.; Los Angeles, CA, USA  90095-1555
Email: jimc@math.ucla.edu    http://www.math.ucla.edu/~jimc (q.v. for PGP key)

Re: is it really better speedstep-ich vs. p4-clockmod cpufreq driver?

[Riccardo Vestrini]

Jim Carter wrote:
> On Thu, 22 Jul 2004, Riccardo Vestrini wrote:
  >>it seems that speedstep-ich and acpi cpufreq driver have only two 
usable clock
>>frequencies, while p4-clockmod has eight
>>my cpu is: Intel Mobile Intel(R) Pentium(R) 4   CPU 3.06GHz stepping 09
> 
> 
> Definitely the voltage modulation is important to have.
you right, but I do not know if it is better to have a 0.3 GHz clock 
most of the time, or a 1.5 GHz with half voltage
> 
> Also as for strategies, if you have dynamic speed modulation, generally if
> the CPU is busy less than 73% of the time, then my machine should be run at
> the lowest speed, whereas if tasks are waiting to run then it should be put
> in the highest speed.  In a typical workload it's very rare for the needed
> throughput to be steadily between 73% and 100% so the intermediate speeds
> could be useful; this is true even if the available speed range is greater.  
> Actually, hardly anyone uses the full capacity of their CPU, and I don't
> even bother to run the dynamic modulation daemon, just leaving it at low
> speed all the time.  I switch manually if I have a big simulation to do.
> 
it is the same for me, cpu is almost always set to the lowest frequency, 
  but I often compile programs, so I need the full power

  I consider strange the fact that a more specific driver 
(speedstep-ich) is not able to put my laptop to half voltage + mininum 
clock (which is 0.3 GHz) while p4-clockmod is only able to adjust clock 
and not voltage;
probably these capabilities can be merged some way ...
I will try to write the authors

thank you

-- 

                                Riccardo Vestrini
                               <riccardov@sssup.it>

"Io ho una deformazione professionale, sono Ingegnere, e il problema in
quello che lei dice è l'essere umano, perché una macchina può sbagliare
ma l'essere umano ha sicuramente molti più difetti" --
sconosciuto ad un congresso, mentre un manager parlava di risorse umane

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