cpupower needs modprobe

[basvandijk]

I noticed the following errors in my journal:

Sep 02 17:58:46 hera systemd[1]: Starting CPU Frequency Governor Setup...
Sep 02 17:58:46 hera cpupower[479]: sh: modprobe: command not found
Sep 02 17:58:46 hera cpupower[479]: Setting cpu: 0
Sep 02 17:58:46 hera cpupower[479]: Error setting new values. Common errors:
Sep 02 17:58:46 hera cpupower[479]: - Do you have proper administration rights? (super-user?)
Sep 02 17:58:46 hera cpupower[479]: - Is the governor you requested available and modprobed?
Sep 02 17:58:46 hera cpupower[479]: - Trying to set an invalid policy?
Sep 02 17:58:46 hera cpupower[479]: - Trying to set a specific frequency, but userspace governor is not available,
Sep 02 17:58:46 hera cpupower[479]: for example because of hardware which cannot be set to a specific frequency
Sep 02 17:58:46 hera cpupower[479]: or because the userspace governor isn't loaded?

This is probably fixed by adding the following to systemd.services.cpufreq in nixos/modules/tasks/cpu-freq.nix:

{ path = [ config.system.sbin.modprobe ]; }

(Note I'm on a recent checkout of nixos-15.09-small)

[vcunat]

Have you tested this fixes the problem? (I'm not really proficient in services, but there seems noone interested.)

[joachifm]

The cpufreq service module adds the governor module to the list of kernel modules to be loaded at bootup, so it should have been loaded by systemd before the cpufreq service runs.

I believe the error is actually a symptom that the ondemand governor is unsupported. Even with modprobe in path, I get the above error when using the ondemand governor. Trying to enable the governor manually (writing directly to /sys) fails as well. The other governors work just fine.

[basvandijk]

@joachifm yes that seems to be the problem.

The powermanagement module is setting the cpuFreqGovernor to ondemand by default.

But that is not supported on my system:

$ cpupower frequency-info | grep available
  available cpufreq governors: performance, powersave

I guess the FIXME in the link I posted relates to this problem.

A workaround for my system would be to set powerManagement.cpuFreqGovernor to one of the available governors. However, it would be better if NixOS would choose powersave instead of ondemand when the system has a modern Intel chip.

[vcunat]

Then I don't know if there is a good common default.

$ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors 
ondemand performance

[joachifm]

Sometimes no fix is the best fix. Maybe document the issue and leave it at that. Then again, cpupower is a fairly trivial sysfs wrapper so it shouldn't be too much work to replicate what it's doing with some additional logic for choosing an appropriate default based on what's available. Not sure if it's worth it, though, but I don't use the upstream powersave module anyways, partly due to this issue.

[pikajude]

@basvandijk, @vcunat: I've also encountered this and am wondering (as somebody who doesn't know anything about cpufreq) what the appropriate fix is.

[basvandijk]

@pikajude as I mentioned above you can just set powerManagement.cpuFreqGovernor to one of the available govenors like:

powerManagement.cpuFreqGovernor = "powersave";