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If you have a new Dothan CPU (Centrino with 2Megs of L2 cache) and kernel 2.6.8, then you will need to apply this patch and this one, too. Otherwise speedstep will not work on your Dothan CPU.

This doesn't apply to kernel 2.6.9 and newer.

Here's a backported (from 2.6.10-mm to 2.6.9) patch. Tested on a X40 running Gentoo Linux. With that patch I'm successfully using the "ondemand" cpufreq governor, which switches the clock of the CPU based on the current workload. Note, that I backported this patch and tested it only on a 1.4 GHz X40 Model.

And here is another report of a successful usage of the latter patch on a 2.0 GHz Dothan (T42p) under 2.6.10.

Using the debian 2.6.16-2-686 kernel on a 2.0 GHz Dothan (T42p) successuflly allows the following options

 available frequency steps: 2.00 GHz, 1.80 GHz, 1.60 GHz, 1.40 GHz, 1.20 GHz, 1000 MHz, 800 MHz, 600 MHz
 available cpufreq governors: userspace, performance
 current policy: frequency should be within 600 MHz and 2.00 GHz.
 current CPU frequency is 600 MHz.

See also

• Pentium M undervolting and underclocking