two same ati cards, xrandr render offload

[Alexandr Gluzskiy]

Good day to all.
i have question about xrandr render offloading feature
i have multihead setup:
xrandr
Screen 0: minimum 320 x 200, current 5120 x 1200, maximum 16384 x 16384
DisplayPort-0 connected 1920x1200+1280+0 (normal left inverted right x 
axis y axis) 518mm x 324mm
    1920x1200     59.95*+
    1920x1080     59.99
    1600x1200     60.00
    1680x1050     59.95
    1600x900      59.98
    1280x1024     60.02
    1440x900      59.89
    1280x800      59.81
    1280x720      59.97
    1024x768      60.00
    800x600       60.32
    640x480       60.00
HDMI-0 connected 1920x1080+3200+0 (normal left inverted right x axis y 
axis) 510mm x 290mm
    1920x1080     60.00*+  50.00    59.94
    1920x1080i    60.00    50.00    59.94
    1680x1050     59.88
    1280x1024     60.02
    1280x960      60.00
    1152x864      59.97
    1280x720      60.00    50.00    59.94
    1024x768      60.00
    800x600       60.32
    720x576       50.00
    720x480       60.00    59.94
    640x480       60.00    59.94
DVI-0 connected 1280x1024+0+0 (normal left inverted right x axis y axis) 
338mm x 270mm
    1280x1024     60.02*+  75.02
    1280x960      60.00
    1152x864      75.00
    1024x768      75.08    70.07    60.00
    832x624       74.55
    800x600       72.19    75.00    60.32    56.25
    640x480       75.00    72.81    66.67    60.00
    720x400       70.08

have one screen in X:

cat /etc/X11/xorg.conf
Section "ServerFlags"
	Option "BlankTime"  "10"
	Option "StandbyTime"  "20"
	Option "SuspendTime"  "30"
	Option "DontZap" "true"
	Option "DRI2" "true"
	Option "DRI3" "false"
	Option "IgnoreABI" "false"
	Option "AutoAddDevices" "true"
	Option "AutoEnableDevices" "true"
	Option "AllowGLXWithComposite" "true"
	Option "AllowMouseOpenFail" "true"
	Option "Clone" "off"
	Option "AIGLX" "on"
##	Option "Pixmap" "32"
	Option "Xinerama" "false"
EndSection

Section "Extensions"
	Option "Composite" "Enable"
#	Option "DAMAGE" "Enable"
#	Option "DOUBLE-BUFFER" "Enable"
#	Option "GLX" "Enable"
#	Option "RANDR" "Enable"
	Option "RENDER" "Enable"
#	Option "XVideo" "Enable"
#	Option "MIT-SHM" "Enable"
#	Option "DPMS" "Enable"
EndSection

Section "Module"
#	Load "dri2"
#	Load "dri3"
#	Load "glamoregl"
	SubSection "extmod"
	    Option  "omit XFree86-DGA"
	EndSubSection
EndSection

Section "Monitor"
	Identifier "DVI-0"
	Option "PreferredMode" "1280x1024"
EndSection

Section "Monitor"
	Identifier "DisplayPort-0"
	Option "PreferredMode" "1920x1200"
	Option "Primary" "true"
EndSection

Section "Monitor"
	Identifier "HDMI-0"
	Option "PreferredMode" "1920x1080"
EndSection

Section "Device"
	Identifier "card1"
	Driver "radeon"
#	Option "EnablePageFlip" "false"
#	Option "Accel" "on"
	Option "DRI3" "off"
	BusID "PCI:1:0:0"
EndSection

Section "Device"
	Identifier "card2"
	Driver "radeon"
#	Option "EnablePageFlip" "false"
#	Option "Accel" "off"
	Option "DRI3" "off"
	BusID "PCI:4:0:0"
EndSection


Section "Screen"
	Identifier "screen1"
	Device "card1"
	Monitor "DVI-0"
	Monitor "DisplayPort-0"
	Monitor "HDMI-0"
	DefaultDepth    24
	SubSection             "Display"
	    Depth               24
	    Virtual 5120 1080
	EndSubSection
EndSection

#Section "Screen"
#	Identifier "screen2"
#	Device "card2"
#	Monitor "DVI-1"
#	DefaultDepth    24
#EndSection

Section "ServerLayout"
	Identifier "main_layout"
	Screen 0 "screen1"
#	Screen 1 "screen2" LeftOf "screen1"
EndSection

Section "dri"
   Mode 0666
EndSection


and here i am not sure if i really need to write anything about second 
gpu in xorg.conf


so, this all working fine and now i want to offload rendering to second 
gpu, for testing, for load balancing (first gpu have much greater 
temperature than second), so i starting to configure via xrandr, and 
stuck on first command:
  xrandr --listproviders
Providers: number : 1
Provider 0: id: 0x58 cap: 0xf, Source Output, Sink Output, Source 
Offload, Sink Offload crtcs: 6 outputs: 3 associated providers: 0 
name:radeon


P.S. sorry for my bad english, it's not my native language