[Bug 48721] New: acpi_cpufreq can't change CPU clock anymore

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=48721

           Summary: acpi_cpufreq can't change CPU clock anymore
           Product: Power Management
           Version: 2.5
    Kernel Version: 3.6.1
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: cpufreq
        AssignedTo: cpufreq@vger.kernel.org
        ReportedBy: mavoga@gmail.com
        Regression: Yes


Created an attachment (id=83121)
 --> (https://bugzilla.kernel.org/attachment.cgi?id=83121)
3.5.5 kernel: output of 'grep -r . /sys/devices/system/cpu/ 2>/dev/null'

On my laptop (a Clevo W150HRM with an i7 2720QM CPU) I'm currently running
Debian wheezy/sid with latest aptosid (3.6-1.slh.3) amd64 kernel: after
switching from 3.5.5 to 3.6 kernel I noticed the idle temperatures suddenly
increased by ~10°C with no apparent activity on the system.

The temperature increase, together with sysfs scaling_cur_freq and
cpuinfo_cur_freq values seem to support my suspect of a cpufreq bug: the
ondemand governor doesn't seem able to modulate the CPU clock anymore. While
the scaling_cur_freq value varies depending on system load just as expected,
the cpuinfo_cur_freq value remains stuck at (or over because of turbo boost)
the maximum CPU frequency, just like the performance governor was set.

I could get the same frequency readings with cpufreq-info, turbostat and i7z:
the CPU frequency never decreases under 2.2GHz.

Furthermore, no cpufreq-set setting seems able to lower the idle frequency in
any way, even by changing governor, and a test 3.6.1 vanilla kernel I compiled
for testing purposes showed the same behavior.

As soon as I reboot to a 3.5.5 kernel cpuinfo_cur_freq begin to follow
scaling_cur_freq just as expected, and the idle temps decrease back by over
10°C.

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