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

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
                              <[email protected]>

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

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: [email protected] http://www.math.ucla.edu/~jimc (q.v. for PGP key)

usable clock

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

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
                              <[email protected]>

"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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