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I have the following problem. As soon as the battery drops below 30%, the CPU is being throttled to 500Mhz. As soon as I plug in the power adapter, it goes back to normal. The laptop is a Lenovo U41-70, I am running Ubuntu 15.10 x64, the CPU is an Intel i3-5020U.

I am not sure if this is helpful, but while it's on battery and below 30%, lscpu (same values from cat /proc/cpuinfo) still gives out:

CPU MHz:               499.984
CPU max MHz:           2200,0000
CPU min MHz:           500,0000

When it's plugged in, CPU MHz immediately jumps up to 2195.015Mhz when there is load on the CPU, which is fine of course.

What could cause this problem? I don't have Windows installed so I don't know if the problem exists there as well.

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  • 1
    have you dug through your BIOS settings? – inanutshellus Feb 1 '16 at 17:45
  • Incidentally, I had an issue like this years ago when my Dell laptop didn't recognize my Dell power cable as being from Dell! It locked my laptop at low-cpu speeds until I found another Dell power cable. Since yours is "only under 30% battery" it won't be your issue, but it's an example of the system taking over at the BIOS level and knee-capping you. – inanutshellus Feb 1 '16 at 17:52
  • lscpu and /proc/cpuinfo are not appropriate tools to monitor your CPU. Checkout your CPU with the proper tool i.e. powertop --> Frequency stats – linrunner Feb 2 '16 at 19:03
  • Thank you! Indeed, lscpu does not seem very accurate, I put the notebook under full load from about 29% to 5% battery, and powertop says 90% at 600MHz and 10% at 500. It looks like everything is alright in the BIOS. – daniel Feb 3 '16 at 15:15
  • As I could not get this problem resolved I will install Windows and see how that goes. This bug/feature/problem makes Ubuntu unusable for me. – daniel Feb 4 '16 at 10:23
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Edit a file

You can always change your clock speed by controlling Intel-pstate.

Intel-pstate can be controlled by changing files in /sys/devices/system/cpu/intel_pstate (Change as root i.e. using sudo)

Use a bash script

You can use this bash file, which I created for my own use. Note that I don't think i3 supports turbo boost.

  1. Download the file from google drive

  2. Run sudo chmod 775 set_cpu_pstate

  3. Execute with sudo ./set_cpu_pstate

  4. Set MAX power to 100

  5. Set MIN power to 100 to force high performance all the time

  6. Enter 1 to activate TurboBoost or 0 to deactivate it

CPU Frequency

You can use i7z for current CPU frequency.

sudo apt-get install i7z
sudo i7z
0

There seems to be a bug in the Lenovo BIOS that initializes the thermal zone limit to passive 0 (/sys/class/thermal/thermal_zone0/trip_point_2_temp), thus tripping overheat policies. If you rmmod then modprobe thermal, it should set you back to normal if you're having this problem on a Lenovo laptop.

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  • That Lenovo BIOS problem manifests itself as a reduction in CPU frequency for each suspend / resume cycle. Myself, I do not believe it to be the same as this problem. I suspect, but have no proof that this is a Clock Modulation when battery low issue. see also. – Doug Smythies Apr 7 '16 at 18:23
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Intel i3-5020U does not support turbo boost manually, means no software as I know something for Intel, but It offers 2 Physical Cores (4 Logical), initially clocked at 2.2GHz, which may go up to ???GHz and 3MB of L3 Cache.

Among its many features, Hyper Threading, and Virtualization are activated. and I don't know but there would be drivers in Ubuntu but you are not able to see the graph like in Windows.

It is something like over clocking in AMD CPU through your BIOS setting if your are an avid gamer you might know this to increase the clock speed in AMD so Intel does not let you over-clock their chip yourself from BIOS settings.

You can check performance of the CPU from System Monitor available with Ubuntu. What I know about you need to have a BIOS update for the systems come pre-installed with Ubuntu and their has to be something to update your BIOS in Ubuntu also to get the full potential of the hardware.

As for wine I will not recommend anyone to update firmware we need something to update BIOS pre-installed with Ubuntu I feel Canonical should and definitely will do something. I also had a very bad experience with Dell,I wish Canonical hardware certification team should have the best guys because I love Ubuntu and it has to be as easy at least on hardware site to upgrade your BIOS using Ubuntu.

You can see about the performance of the CPU at Ark-Intel also.

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