Problem with CPU frequency scaling

2011-01-14T01:22:44Z

Xarlith: working solution: thinkpad power manager for windows allows some PC's to run with full freq on 65W adaptor. same thing is possible in linux only with this fix. thats why this solution should be here.

{{stub}}

{{WARN|CPU frequency limitation is a safety feature of your ThinkPad, do not work around it! If you have set the BIOS to performance mode and it is still limiting maximum CPU frequency, there is almost always a damn good reason for that}}

==Symptom==
If the battery pack is removed and the laptop is powered by a 65W AC adapter only, the CPU downclocks to the lowest multiplier and remains locked in low speed. This happens irrespective of the scaling method in use (kernelspace or userspace) and of the frequency governor selected (ondemand, performance, etc.).

Output of cpufreq-info (on AC power without battery):

analyzing CPU 0:
driver: centrino
CPUs which need to switch frequency at the same time: 0 1
hardware limits: 1000 MHz - 1.83 GHz
available frequency steps: 1.83 GHz, 1.33 GHz, 1000 MHz
available cpufreq governors: ondemand, userspace, powersave, performance
'''current policy: frequency should be within 1000 MHz and 1000 MHz.'''
The governor "ondemand" may decide which speed to use
within this range.
current CPU frequency is 1000 MHz (asserted by call to hardware).

analyzing CPU 1:
driver: centrino
CPUs which need to switch frequency at the same time: 0 1
hardware limits: 1000 MHz - 1.83 GHz
available frequency steps: 1.83 GHz, 1.33 GHz, 1000 MHz
available cpufreq governors: ondemand, userspace, powersave, performance
'''current policy: frequency should be within 1000 MHz and 1000 MHz.'''
The governor "ondemand" may decide which speed to use
within this range.
current CPU frequency is 1000 MHz (asserted by call to hardware).

Output of cpufreq-info (on AC power with battery plugged in):

analyzing CPU 0:
driver: centrino
CPUs which need to switch frequency at the same time: 0 1
hardware limits: 1000 MHz - 1.83 GHz
available frequency steps: 1.83 GHz, 1.33 GHz, 1000 MHz
available cpufreq governors: ondemand, userspace, powersave, performance
'''current policy: frequency should be within 1000 MHz and 1.83 GHz.'''
The governor "ondemand" may decide which speed to use
within this range.
current CPU frequency is 1000 MHz (asserted by call to hardware).

analyzing CPU 1:
driver: centrino
CPUs which need to switch frequency at the same time: 0 1
hardware limits: 1000 MHz - 1.83 GHz
available frequency steps: 1.83 GHz, 1.33 GHz, 1000 MHz
available cpufreq governors: ondemand, userspace, powersave, performance
'''current policy: frequency should be within 1000 MHz and 1.83 GHz.'''
The governor "ondemand" may decide which speed to use
within this range.
current CPU frequency is 1000 MHz (asserted by call to hardware).

==Explanation==

The 65W AC adaptor does not supply enough power to handle peak power draws from the CPU/disk/GPU on the later ThinkPads. The battery is required to supply the peak demand and ensure correct system operation.

Messing with this can cause data loss, data corruption, and hardware damage.

==Solution==

Make sure no BIOS setting is limiting the CPU frequency range (like "thermal management" = "BALANCED").

# Buy a 90W AC adapter
# Don't use the laptop without the battery pack

Other solution than using the laptop with the battery pack always inserted is to add "processor.ignore_ppc=1" to kernel boot command line. This allows to disable BIOS frequency limit, but can be mischievous to the computer if it's power consumption is higher than 65W.

== Affected Models ==

* {{Z61m}}
* {{T61}}
* {{T60p}}

Probably ALL Lenovo ThinkPads. One can actually track this through the DSDT, but it is not worth the effort.

ThinkWiki - User contributions [en]

Problem with CPU frequency scaling