Bug 51741

Summary:	powernow-k8 calls for acpi-cpufreq but doesn’t warn if it’s not available
Product:	Power Management	Reporter:	Andreas (andreas.thalhammer)
Component:	cpufreq	Assignee:	cpufreq
Status:	CLOSED PATCH_ALREADY_AVAILABLE
Severity:	normal	CC:	florian, fredlwm+others, lenb
Priority:	P1
Hardware:	All
OS:	Linux
Kernel Version:	3.7.0	Subsystem:
Regression:	No	Bisected commit-id:

Description Andreas 2012-12-16 16:03:46 UTC

On my system, I used to have powernow-k8 compiled into the kernel, but not acpi-cpufreq. I run Gentoo Linux.

With sys-kernel/gentoo-sources-3.6.8, I got the following relevent dmesg output:
powernow-k8: Found 1 AMD Phenom(tm) II X6 1090T Processor (6 cpu cores) (version 2.20.00)
powernow-k8: Core Performance Boosting: on.
powernow-k8:    0 : pstate 0 (3200 MHz)
powernow-k8:    1 : pstate 1 (2400 MHz)
powernow-k8:    2 : pstate 2 (1600 MHz)
powernow-k8:    3 : pstate 3 (800 MHz)

Now, with sys-kernel/gentoo-sources-3.7.0, dmesg showed the following:
powernow-k8: this CPU is not supported anymore, using acpi-cpufreq instead.

This lead me into thinking that acpi-cpufreq was used when it actually wasn’t, because it was missing in my kernel (since I don’t know all config options by heart: I had to check for that).

I found that the fans were a bit noisier than normal, so I looked in /proc/cpuinfo, which showed all 6 cores were at 3.2 GHz.

I then recompiled the kernel with acpi-cpufreq compiled in and removed powernow-k8. Now /proc/cpuinfo shows 800 MHz on all or most of the cores when the system is mostly idle.

Apparently, acpi-cpufreq doesn’t show any output at all, except:
acpi-cpufreq: overriding BIOS provided _PSD data

My suggestion would be to make powernow-k8 check for the availability of acpi-cpufreq and print out a warning should it not be available.
And I also suggest a short “acpi-cpufreq is used for frequency scaling” so one can see that it was loaded alright.

Comment 1 Andreas 2013-01-24 22:18:27 UTC

This should be fixed now.

The patch titled

    powernow-k8: Add a kconfig dependency on acpi-cpufreq

was added to the 3.7-stable tree.

The filename of the patch is:
     powernow-k8-add-a-kconfig-dependency-on-acpi-cpufreq.patch
and it can be found in the queue-3.7 subdirectory.

Since 3.7.4 is already out, I assume it will be part of 3.7.5 and later.

Comment 2 Florian Mickler 2013-01-26 10:50:08 UTC

A patch referencing this bug report has been merged in Linux v3.8-rc5:

commit 631e8ac18fd59722e7ceb15fceeef3f368c250f9
Author: Borislav Petkov <bp@suse.de>
Date:   Fri Jan 18 00:19:37 2013 +0100

    powernow-k8: Add a kconfig dependency on acpi-cpufreq

Comment 3 Frédéric L. W. Meunier 2013-02-12 20:12:41 UTC

After running 'make oldconfig' from 3.7.3 to 3.7.7, it silently removed the "CONFIG_X86_POWERNOW_K8=m" line from .config.

I would expect it to add the new dependencies.