[SOLVED] CPU frequency decreases under load, rises when idle

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[SOLVED] CPU frequency decreases under load, rises when idle

Postby terdon on Tue Mar 27, 2012 11:46 am

Hello all, I have a strange problem. As it says in the title, my cpu frequency will decrease when the system is under load. The problem seems to be that the BIOS reports different max cpu freqs depending on whether the system is under load. The details given below show the "performance" governor but I get similar behaviour with userspace and ondemand. In all cases, I cannot override the BIOS limit if that is set to the low value (see below).

I get the same problem using either 3.0.0-1-amd64 or 3.2.0-2-amd64 kernels. I have just updated my BIOS and saw no difference. I have tried disabling dynamic frequency by disabling Intel SpeedStep Technology in the BIOS. I got a similar situation. In this case, the CPU was reporting a constant frequency of 2.67 GHz but minor tasks (eg firefox, conky, emacs) would occupy >20% of CPU and the CPU usage would quickly reach 99%. I mean that before running "stress" or similar, firefox was sitting happily at ~6% CPU, As soon as I started stressing the system, firefox shot up to ~20% despite the CPU freq apparently not changing. This seems to imply that the CPU freq is misreported and disabling Intel SpeedStep does not stop the decrease in freq, just stops the system from reporting it.

So, either using dynamic frequency or not, my system becomes unusable when even under minor processor loads. Does anyone have any ideas how to fix this? I seem to recall there are known regressions in the 3.0-3.2 kernels that could affect CPU frequency control. Anybody know if that is true? Should I just wait for 3.3?

System Specs:
Dell M4500
Intel Core i7 M 620 @ 2.67GHz
4GB RAM
LMDE, 3.2.0-2-amd64
BIOS: Dell Inc. A10 11/30/2011


Details when using "performace" governor:
1. System idle:
cpufreq-info output (for one processor):
Code: Select all
cpufrequtils 007: cpufreq-info (C) Dominik Brodowski 2004-2009
Report errors and bugs to cpufreq@vger.kernel.org, please.
analyzing CPU 0:
  driver: acpi-cpufreq
  CPUs which run at the same hardware frequency: 0 1 2 3
  CPUs which need to have their frequency coordinated by software: 0
  maximum transition latency: 10.0 us.
  hardware limits: 1.20 GHz - 2.67 GHz
  available frequency steps: 2.67 GHz, 2.67 GHz, 2.53 GHz, 2.40 GHz, 2.27 GHz, 2.13 GHz, 2.00 GHz, 1.87 GHz, 1.73 GHz, 1.60 GHz, 1.47 GHz, 1.33 GHz, 1.20 GHz
  available cpufreq governors: userspace, conservative, powersave, ondemand, performance
  current policy: frequency should be within 1.20 GHz and 2.27 GHz.
                  The governor "performance" may decide which speed to use
                  within this range.
  current CPU frequency is 2.27 GHz.
  cpufreq stats: 2.67 GHz:64.78%, 2.67 GHz:0.81%, 2.53 GHz:1.03%, 2.40 GHz:0.45%, 2.27 GHz:1.38%, 2.13 GHz:1.25%, 2.00 GHz:0.66%, 1.87 GHz:0.48%, 1.73 GHz:0.43%, 1.60 GHz:1.20%, 1.47 GHz:0.80%, 1.33 GHz:0.77%, 1.20 GHz:25.95%  (450)


cat /sys/devices/system/cpu/cpu0/cpufreq/bios_limit
Code: Select all
2667000


2. System under load
In this example, I am running stress but anything can trigger this. Even pasting large amounts of data into a terminal(!):
Code: Select all
stress --cpu 8 --io 4 --vm 2 --vm-bytes 128M --timeout 10s


Relevant lines of cpufreq-info output:
Code: Select all
 cpufrequtils 007: cpufreq-info (C) Dominik Brodowski 2004-2009
Report errors and bugs to cpufreq@vger.kernel.org, please.
analyzing CPU 0:
  driver: acpi-cpufreq
  CPUs which run at the same hardware frequency: 0 1 2 3
  CPUs which need to have their frequency coordinated by software: 0
  maximum transition latency: 10.0 us.
  hardware limits: 1.20 GHz - 2.67 GHz
  available frequency steps: 2.67 GHz, 2.67 GHz, 2.53 GHz, 2.40 GHz, 2.27 GHz, 2.13 GHz, 2.00 GHz, 1.87 GHz, 1.73 GHz, 1.60 GHz, 1.47 GHz, 1.33 GHz, 1.20 GHz
  available cpufreq governors: userspace, conservative, powersave, ondemand, performance
  current policy: frequency should be within 1.20 GHz and 1.20 GHz.
                  The governor "performance" may decide which speed to use
                  within this range.
  current CPU frequency is 1.20 GHz.
  cpufreq stats: 2.67 GHz:60.05%, 2.67 GHz:0.75%, 2.53 GHz:2.21%, 2.40 GHz:0.98%, 2.27 GHz:2.46%, 2.13 GHz:1.18%, 2.00 GHz:0.64%, 1.87 GHz:0.47%, 1.73 GHz:0.42%, 1.60 GHz:1.14%, 1.47 GHz:0.77%, 1.33 GHz:0.73%, 1.20 GHz:28.19%  (462)

cat /sys/devices/system/cpu/cpu0/cpufreq/bios_limit
Code: Select all
1199000
Last edited by terdon on Thu Mar 29, 2012 1:41 pm, edited 1 time in total.
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Re: CPU frequency decreases under load, rises when idle

Postby I_can_see_the_light on Thu Mar 29, 2012 5:42 am

I was going to suggest that you tried using the "ondemand" governor, but then I saw that you already tried that. I really don't know what to say... There are a couple of other cpu frequency scaling applications in the repo, perhaps one of those might help?
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Re: CPU frequency decreases under load, rises when idle

Postby terdon on Thu Mar 29, 2012 1:41 pm

Yes, I've tried just about everything I could think of except the obvious: I raised the laptop off the surface of the desk, thereby increasing airflow. Problem solved!

Grrr...so what was happening is that the CPU would overheat and the BIOS would cick in and lower the frequency. Nothing to do with any kernel level processes after all. The annoying thing is that the laptop is not that dirty. I opened it and it seems relatively ok. I may have to replace the conductive paste on the CPU though. $#%&@!, Marking as solved...
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Re: CPU frequency decreases under load, rises when idle

Postby I_can_see_the_light on Thu Mar 29, 2012 3:22 pm

terdon wrote:Yes, I've tried just about everything I could think of except the obvious: I raised the laptop off the surface of the desk, thereby increasing airflow. Problem solved!

Grrr...so what was happening is that the CPU would overheat and the BIOS would cick in and lower the frequency. Nothing to do with any kernel level processes after all. The annoying thing is that the laptop is not that dirty. I opened it and it seems relatively ok. I may have to replace the conductive paste on the CPU though. $#%&@!, Marking as solved...

Strange that it should overheat just by standing on the desk though...
Fujitsu Siemens Lifebook E8020D (triple booting Ubuntu, CrunchBang & Win 7)

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Re: [SOLVED] CPU frequency decreases under load, rises when

Postby terdon on Thu Mar 29, 2012 3:30 pm

I agree. However, my desk is not really a proper desk, just a plank of wood. It is quite flexible, maybe the fan exit is blocked because of that flexibility?

And in any case, it only heats up when being used. Idle(ish) is ok. I have no problems running a few firefox tabs terminal and emacs windows. If I try a video or run a script or something it hangs.

Good news is that the laptop was bought by my lab and is still covered by the guarantee. I opened this thread to see if anyone could come up with a software solution :)
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Re: [SOLVED] CPU frequency decreases under load, rises when

Postby I_can_see_the_light on Thu Mar 29, 2012 3:39 pm

terdon wrote:I agree. However, my desk is not really a proper desk, just a plank of wood. It is quite flexible, maybe the fan exit is blocked because of that flexibility?

Yeah that's possible. If the edge is a little rough I assume the airflow would suffer, so your solution sounds good. :)
Fujitsu Siemens Lifebook E8020D (triple booting Ubuntu, CrunchBang & Win 7)

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Re: [SOLVED] CPU frequency decreases under load, rises when

Postby terdon on Thu Mar 29, 2012 4:18 pm

You could try it if you have a similar problem. Then you might see the light shining under your laptop.

Sorry, couldn't resist, I'm a sucker for bad jokes :)
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Re: [SOLVED] CPU frequency decreases under load, rises when

Postby I_can_see_the_light on Thu Mar 29, 2012 4:49 pm

Bad jokes are underestimated :D

But as a matter of fact, I did buy a laptop stand last summer to make the laptop run cooler. I later found out that adding the parameter pcie_aspm=force to /etc/default/grub did wonders not only to battery life, but also lowered the fan noise and reduced the heat.

EDIT: 100 posts! :mrgreen: :mrgreen:
Fujitsu Siemens Lifebook E8020D (triple booting Ubuntu, CrunchBang & Win 7)

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Re: [SOLVED] CPU frequency decreases under load, rises when

Postby terdon on Thu Mar 29, 2012 4:51 pm

He, kudos on your posts.

I already had pcie_aspm=force and i915.i915_enable_rc6=1 in grub. May have helped a little for my battery/fan isues but I am not sure.
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