atitweak -e 900 -m 800 -f 80

C:\Python27\Scripts>python atitweak -l
0. AMD Radeon HD 6900 Series (\\.\DISPLAY1)
    engine clock range is 125 - 950MHz
    memory clock range is 75 - 1450MHz
    core voltage range is 0.9 - 1.175VDC
    performance level 0: engine clock 250MHz, memory clock 150MHz, core voltage 0.9VDC
    performance level 1: engine clock 500MHz, memory clock 790MHz, core voltage 1VDC
    performance level 2: engine clock 915MHz, memory clock 790MHz, core voltage 1.175VDC
    fan speed range: 0 - 100%,  800 - 6000 RPM

C:\Python27\Scripts>

C:\Python27\Scripts>python atitweak -e 900 --adapter=all
Setting performance level 0 on adapter 0: engine clock 900MHz
Setting performance level 1 on adapter 0: engine clock 900MHz
Setting performance level 2 on adapter 0: engine clock 900MHz

C:\Python27\Scripts>python atitweak -e 900 -A 1

C:\Python27\Scripts>python atitweak -e 900 -A 2

C:\Python27\Scripts>python atitweak -e 915 -A 0
Setting performance level 0 on adapter 0: engine clock 915MHz
Setting performance level 1 on adapter 0: engine clock 915MHz
Setting performance level 2 on adapter 0: engine clock 915MHz

C:\Python27\Scripts>

# atitweak -l
No protocol specified
Couldn't initialize ADL interface.

# DISPLAY=:0 atitweak -l
No protocol specified
Couldn't initialize ADL interface.

# atitweak -h
Usage: atitweak [options]

Options:
  -h, --help            show this help message and exit
  -l, --list-adapters   Lists all detected and supported display adapters.
  -s, --status          Shows current clock speeds, core voltage, utilization
                        and performance level.
  -e ENGINE_CLOCK, --set-engine-clock=ENGINE_CLOCK
                        Sets engine clock speed (in MHz) for the selected
                        performance levels on the selected adapters.
  -m MEMORY_CLOCK, --set-memory-clock=MEMORY_CLOCK
                        Sets memory clock speed (in MHz) for the selected
                        peformance levels on the selected adapters.
  -v CORE_VOLTAGE, --set-core-voltage=CORE_VOLTAGE
                        Sets core voltage level (in VDC) for the selected
                        performance levels on the selected adapters.
  -f FAN_SPEED, --set-fan-speed=FAN_SPEED
                        Sets the fan speed (in percent) for the selected
                        adapters.
  -d, --set-fan-speed-default
                        Resets the fan speed to its default setting.
  -A ADAPTERLIST, --adapter=ADAPTERLIST
                        Selects which adapters returned by --list-adapters
                        should be affected by other atitweak options.
                        ADAPTERLIST contains either a comma-seperated sequence
                        of the index numbers of the adapters to be affected or
                        else contains the keyword "all" to select all the
                        adapters. If --adapter is missing, all adapters will
                        be affected.
  -P PERFORMANCELEVELLIST, --performance-level=PERFORMANCELEVELLIST
                        Selects which performance levels returned by --list-
                        adapters should be affected by other atitweak options.
                        PERFORMANCELEVELLIST contains either a comma-separated
                        sequence of the index numbers of the performance
                        levels to be affected or else contains the keyword
                        "all" to select all performance levels. If
                        --performance-level is missing, all performance levels
                        will be affected.

# aticonfig --lsa
* 0. 08:00.0 AMD Radeon HD 6990
  1. 07:00.0 AMD Radeon HD 6990

* - Default adapter

# aticonfig --odgc --adapter=all
ERROR - X needs to be running to perform ATI Overdrive(TM) commands

ssh -X user@<your_ip>
password: <your_user_password>
sudo su
chmod uog+rwdev/ati/card*
xauth mergehome/user/.Xauthority
export DISPLAY=:0
aticonfig --odgc --adapter=all