I found out today how to set the real time clock max frequencies in Ubuntu since they removed the possibility to do it from
sysutil.conf from newer kernels. Add the following to your
/etc/rc.local or another startup script:
echo 2048 >/sys/class/rtc/rtc0/max_user_freq echo 2048 >/proc/sys/dev/hpet/max-user-freq
Reboot, and you should get better performance from things like mplayer.