Arch Linux

jbromley

Member

From: Pasadena, CA

Registered: 2007-02-04

Posts: 268

cpu frequency scaling doesn't work while on battery

The subject pretty much describes it. I've got a ThinkPad T43 with a Pentium M 2GHz running the latest Arch kernel, and when I'm on battery CPU frequency scaling does not work at all. It works just fine as long as the machine is running on AC power.

When I'm on battery, no matter which governor I use and how much load I put on the machine, the CPU frequency stays at 800MHz, which is the lowest clock speed for my machine. Even when I set the governor to performance, which should always run the machine at the maximum frequency, the clock stays at 800MHz. I've tried using the userspace governor as well and manually setting the frequency, but this does not work either. Nonetheless, as soon as I plug in the power cord, the frequency scaling kicks in and works fine.

As far as I can tell, this seems to be a problem since 2.6.25, but on lkml I didn't see any questions about this, so perhaps this is something in the Arch kernel? I don't expect I'll be able to fix this, but at least it would be nice to know if others have the same problem so bug reports could be made to the pertinent places.

Regards.
j

mfa

Member

Registered: 2007-10-04

Posts: 19

Re: cpu frequency scaling doesn't work while on battery

Hi there!

I'm running Arch on my Thinkpad R52 with an Pentium M 1,73 GHz. Frequency scaling works for me, no matter if plugged or running on battery. However I am using a self configured kernel and not the arch stock kernel.

What came to my mind is, that there is a BIOS setting for the cpu scaling for battery. Have you checked this? I don't know if this can be or is overridden by the kernel. Well, just an idea.

Cheers,
mfa

jbromley

Member

From: Pasadena, CA

Registered: 2007-02-04

Posts: 268

Re: cpu frequency scaling doesn't work while on battery

Well, I checked my BIOS and there was an option for the type of battery power management, but it was set to automatic, just like for AC power. I believe the OS overrides this anyway. Also, this used to work in the past and I haven't made any BIOS changes, so it appears it was broken by some (recent) new kernel. Thanks for the suggestion, though.

Regards.

.:B:.

Forum Fellow

Registered: 2006-11-26

Posts: 5,819

Website

Re: cpu frequency scaling doesn't work while on battery

Did you install any powersaving daemons by any chance?

You probably need to reconfigure cpufreq's profiles. Changing governors with cpufrequtils won't help much if cpufreqd is still running.

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jbromley

Member

From: Pasadena, CA

Registered: 2007-02-04

Posts: 268

Re: cpu frequency scaling doesn't work while on battery

No, I haven't installed any power saving daemons. I like things simple, so I let the kernel governor control the CPU frequency. The only thing I do is launch cpufreq at boot to set the proper governor and then use ACPI events to switch between the ondemand and conservative governors for AC/battery operation. The only other thing I have installed that might make a difference is laptop-mode. However, I do not use laptop-mode's frequency controller since I've had problems with it in the past. I will shut down laptop-mode and see what happens.

The other thing is that frequency scaling works if the AC cord is plugged in and it used to work on battery also. It seems the upgrade to kernel 2.6.25 hosed things. Everything looks good when I do cpufreq-info, but the frequency never changes from 800 MHz.

At this point I'm hoping that the next version of the kernel fixes things.