# [Solved] Power Management Dell PE2850

## keola

Anyone have one of these? I have tried everything I can find to throttle the CPU's. All I can manage to do is run the performance mode governor! it says it will go down the 375Mhz... but I'm stuck at 3Ghz! 

this machine does almost nothing (CPU wise) and draws a lot of power  :Sad: 

Just wondering if anyone has been able to do this?

- running kernel 2.6.30 something

Thanks!Last edited by keola on Tue Nov 10, 2009 12:01 am; edited 1 time in total

----------

## eccerr0r

If you're that worried about power on one machine, please note that a CPU running HLTs at 3GHz versus a CPU running HLTs at 375MHz is not all that big a difference the MHz difference makes it sounds.  This is because leakage power when running HLTs tend to overshadow the power consumed by running the HLT instructions.    This is what I found when comparing my 2.4GHz P4 (overclocked to 3.1GHz) and using P4 Clock scaling and using the OnDemand governor running the CPU at 300MHz (387MHz o/c).  This is wall measured power through line power.

In any case, do you see the other governors in the available governors procfs file?  Are you using the right driver?

I've noticed many BIOS do not support ACPI clock scaling properly... so this is also BIOS dependent.  But the P4 clock throttling should work on all P4's.  I don't know if this works on Core2 machines though, never got it to work.

----------

## keola

So sounds like you are saying it will not run any cooler? either way I would like to see this working, but...

```
current policy: frequency should be within 375 MHz and 3.00 GHz.

                  The governor "userspace" may decide which speed to use

                  within this range.

  current CPU frequency is 3.00 GHz (asserted by call to hardware).

  cpufreq stats: 375 MHz:0.00%, 750 MHz:0.00%, 1.13 GHz:0.00%, 1.50 GHz:0.00%, 1.88 GHz:0.00%, 2.25 GHz:0.00%, 2.63 GHz:0.00%, 3.00 GHz:100.00%

alpha ~ # cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed

375000

```

p4-clockmod is in use - but I get errors about all the governors except userspace and performance

I don't think it is obeying anything...

----------

## eccerr0r

That's right, it will not run (much) cooler, as far as I can tell on my P4.  I could barely tell the difference in power consumption and I didn't really see much temperature change.  HLT (Halt) are run during times of inactivity by Linux when there's nothing on the run queue.  When HLT is run, machine drops into low power state which is marginally affected by clock speed.

Granted if your CPU was at 100% utilization at 375MHz versus 3GHz, the latter case would be considerably warmer.  However the computer would be finished with the computation 8 times faster, and ready to get into running HLTs again.  Tradeoff...

I normally use the 'ondemand' governor.  Do you have this compiled into the kernel or module for it inserted?  I've never tried userspace...  I figure that if I need to crunch numbers at low latency (changing clock speeds takes some stabilization time) I manually force it to performance mode.

The other issue I've had is that if I have anything running, 'ondemand' will likely switch to full speed more often.  Consider interrupts which can take it out of powersave.

----------

## keola

hmm.. well thanks for the info! I was able to get sensor info via ipmi - but I did update the bios a06 to a07 and the fans appear to run faster now  :Sad: 

As far as the throttling goes, sounds like it is not worth it...

Thanks again!

----------

## eccerr0r

If you have a lot of machines or want to squeeze every little bit out, it still could be helpful, as depending on the system, "high power" mode may actually use more power relatively than using low power for longer.

I found the difference on my P4 (it was a PVR) to be less than a watt or so (on whole system, measured by a crude system: an ammeter, and the resolution is dicey down there.) ... less than 1% overall on total consumption (leakage, HDD, MB, fans, RAM, Video, etc.), plus I get problems when the machine wakes up and does timing, causing my recordings to sometimes be computed incorrectly.  I suppose for a non timing-critical, computation-only server it  makes more sense but it caused that weird issue sometimes (Abit IS7 motherboard, P4-2.4B).

----------

## keola

The machine does not do much at all, I figured if I could slow it down, I could make it cooler. I was able to get clockmods working, a bit buggy (the methods and results - not the machine) but it was indeed running a lower speed.

and with being forced to use userspace, very pointless

----------

