Bug 202651 - cpufreq no longer works in 10.2 on Intel D525MWV
Summary: cpufreq no longer works in 10.2 on Intel D525MWV
Status: New
Alias: None
Product: Base System
Classification: Unclassified
Component: kern (show other bugs)
Version: 10.2-RELEASE
Hardware: amd64 Any
: --- Affects Only Me
Assignee: freebsd-bugs (Nobody)
Keywords: regression
Depends on:
Reported: 2015-08-25 11:53 UTC by Viktor Štujber
Modified: 2020-05-30 15:56 UTC (History)
0 users

See Also:


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Description Viktor Štujber 2015-08-25 11:53:25 UTC
After updating from 10.1-RELENG (2014-12-07) to 10.2-RELEASE, I can no longer manage the CPU's frequency.

kernel: Starting powerd.
kernel: powerd: no cpufreq(4) support -- aborting: No such file or directory

This is the consequence of sysctls 'dev.cpu.X.freq' and 'dev.cpu.X.freq_levels' not being registered, indicating a problem with the 'cpufreq' module. I built/installed a clean GENERIC kernel and all available modules, but the problem still persists.

I tried setting sysctl debug.cpufreq.verbose=1, which according to sys/kern/kern_cpu.c activates CF_DEBUG() calls. But the message in cpufreq_attach(), that should say "cpufreq: initializing %s", does not show up. I don't know if this means that the module doesn't even try to load. Help would be appreciated.
Comment 1 Viktor Štujber 2015-10-07 23:18:38 UTC
After failing to find the regression window and discovering that the previous kernel with the new userland also exhibits the problem, I again tried searching for existing discussions about the subject.

I found https://lists.freebsd.org/pipermail/freebsd-stable/2015-March/082034.html from march 2015 which points to a 1 year old change in HEAD, https://svnweb.freebsd.org/base?view=revision&revision=265329 . Here the committer references some other mailing list discussion, which concluded that P-state power management is not effective and can interfere with C-state power management.

That is nice and all, but this Intel Atom CPU does not have any C-state power management. Using P-states has a measurable impact (a few watts). Undoing the changes to /boot/device.hints is what I did for now.
Comment 2 Martin Birgmeier 2015-10-26 11:10:26 UTC
How do you load cpufreq?

Could it be https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=180588?

-- Martin
Comment 3 Viktor Štujber 2015-10-26 11:14:11 UTC
Unrelated. I use the default kernconf which compiles cpufreq into the kernel.