If you are running the cpufreq to manage your CPU, there are a number of governors that control how it's used. E.g. "performance" will thrash the processor, "conservative" won't and "ondemand" will scale the frequency as appropriate for the task in hand.
To see which governors are available and which your system is using, run the following command:
cpufreq-info
Example output, where I run the command 3 times in a row as demand on the processor increases:
slap steph # cpufreq-info cpufrequtils 002: cpufreq-info (C) Dominik Brodowski 2004-2006 Report errors and bugs to linux@brodo.de, please. analyzing CPU 0: driver: centrino CPUs which need to switch frequency at the same time: 0 hardware limits: 800 MHz - 2.00 GHz available frequency steps: 2.00 GHz, 1.60 GHz, 1.33 GHz, 1.07 GHz, 800 MHz available cpufreq governors: conservative, ondemand, powersave, userspace, performance current policy: frequency should be within 800 MHz and 2.00 GHz. The governor "ondemand" may decide which speed to use within this range. current CPU frequency is 800 MHz (asserted by call to hardware). slap steph # cpufreq-info cpufrequtils 002: cpufreq-info (C) Dominik Brodowski 2004-2006 Report errors and bugs to linux@brodo.de, please. analyzing CPU 0: driver: centrino CPUs which need to switch frequency at the same time: 0 hardware limits: 800 MHz - 2.00 GHz available frequency steps: 2.00 GHz, 1.60 GHz, 1.33 GHz, 1.07 GHz, 800 MHz available cpufreq governors: conservative, ondemand, powersave, userspace, performance current policy: frequency should be within 800 MHz and 2.00 GHz. The governor "ondemand" may decide which speed to use within this range. current CPU frequency is 1.60 GHz (asserted by call to hardware). slap steph # cpufreq-info cpufrequtils 002: cpufreq-info (C) Dominik Brodowski 2004-2006 Report errors and bugs to linux@brodo.de, please. analyzing CPU 0: driver: centrino CPUs which need to switch frequency at the same time: 0 hardware limits: 800 MHz - 2.00 GHz available frequency steps: 2.00 GHz, 1.60 GHz, 1.33 GHz, 1.07 GHz, 800 MHz available cpufreq governors: conservative, ondemand, powersave, userspace, performance current policy: frequency should be within 800 MHz and 2.00 GHz. The governor "ondemand" may decide which speed to use within this range. current CPU frequency is 2.00 GHz (asserted by call to hardware).