Using two graphics cards with Xorg-X11

jrtayloriv · 01-01-2007, 03:20 PM

Is it possible to configure X to use two graphics cards? I have a Compaq Evo N600C laptop, with an ATI Radeon Mobility M6 LY that is working fine with Xorg-X11, using the open-source radeon drivers. But I have noticed that my Intel 830M motherboard also has AGP 4X capability and was wondering if there is any way to configure X to use both graphics cards at the same time for increased performance. If this is possible, what do I need to do to configure Xorg-X11 to do it? Will I have to reinstall with different VIDEO_CARD in /etc/make.conf?

Here is the relevant output from lspci -vv:

Code:

00:00.0 Host bridge: Intel Corporation 82830 830 Chipset Host Bridge (rev 02)
        Subsystem: Compaq Computer Corporation Evo N600c
        Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B-
        Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort+ >SERR- <PERR-
        Latency: 0
        Region 0: Memory at 60000000 (32-bit, prefetchable) [size=256M]
        Capabilities: [40] Vendor Specific Information
        Capabilities: [a0] AGP version 2.0
                Status: RQ=32 Iso- ArqSz=0 Cal=0 SBA+ ITACoh- GART64- HTrans- 64bit- FW+ AGP3- Rate=x1,x2,x4
                Command: RQ=1 ArqSz=0 Cal=0 SBA+ AGP+ GART64- 64bit- FW- Rate=x4

00:01.0 PCI bridge: Intel Corporation 82830 830 Chipset AGP Bridge (rev 02) (prog-if 00 [Normal decode])
        Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B-
        Status: Cap- 66MHz+ UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR-
        Latency: 64
        Bus: primary=00, secondary=01, subordinate=01, sec-latency=0
        I/O behind bridge: 00003000-00003fff
        Memory behind bridge: 40200000-402fffff
        Prefetchable memory behind bridge: 48000000-4fffffff
        Secondary status: 66MHz+ FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort+ <SERR- <PERR-
        BridgeCtl: Parity- SERR- NoISA+ VGA+ MAbort- >Reset- FastB2B-

00:1e.0 PCI bridge: Intel Corporation 82801 Mobile PCI Bridge (rev 41) (prog-if 00 [Normal decode])
        Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B-
        Status: Cap- 66MHz- UDF- FastB2B+ ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR-
        Latency: 0
        Bus: primary=00, secondary=02, subordinate=07, sec-latency=32
        I/O behind bridge: 00002000-00002fff
        Memory behind bridge: 40000000-401fffff
        Prefetchable memory behind bridge: 20000000-23ffffff
        Secondary status: 66MHz- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort+ <SERR- <PERR-
        BridgeCtl: Parity- SERR+ NoISA+ VGA- MAbort- >Reset- FastB2B-

01:00.0 VGA compatible controller: ATI Technologies Inc Radeon Mobility M6 LY (prog-if 00 [VGA])
        Subsystem: Compaq Computer Corporation Evo N600c
        Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping+ SERR- FastB2B-
        Status: Cap+ 66MHz+ UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR-
        Latency: 66 (2000ns min), Cache Line Size 08
        Interrupt: pin A routed to IRQ 11
        Region 0: Memory at 48000000 (32-bit, prefetchable) [size=128M]
        Region 1: I/O ports at 3000 [size=256]
        Region 2: Memory at 40200000 (32-bit, non-prefetchable) [size=64K]
        [virtual] Expansion ROM at 40220000 [disabled] [size=128K]
        Capabilities: [58] AGP version 2.0
                Status: RQ=48 Iso- ArqSz=0 Cal=0 SBA+ ITACoh- GART64- HTrans- 64bit- FW- AGP3- Rate=x1,x2,x4
                Command: RQ=32 ArqSz=0 Cal=0 SBA+ AGP+ GART64- 64bit- FW- Rate=x4
        Capabilities: [50] Power Management version 2
                Flags: PMEClk- DSI- D1+ D2+ AuxCurrent=0mA PME(D0-,D1-,D2-,D3hot-,D3cold-)
                Status: D0 PME-Enable- DSel=0 DScale=0 PME-

Thanks,
jrtayloriv

PTrenholme · 01-01-2007, 03:47 PM

You should be able to do so, but I'm not sure what you mean by "at the same time for increased performance." The only way I could see this working would be if the two devices were driving different displays, or different parts of the same display (although that may not be possible). But driving two (or more) different displays with different cards is often done.

The problem with using two different cards for the same display is that the cards will both be changing the same block of display memory, and the only way to coordinate those changes would be to let each card lock the memory while writing its changes. This would result, I suspect, in a severe decrease in performance.

And, of course, you'd need to re-write the device drivers for both cards to handle the multiprocessing overhead. Again, probably a performance hit.

jrtayloriv · 01-01-2007, 04:37 PM

OK, I didn't know about how video cards accessed display memory. So obviously this is not possible.

Thanks anyway,
jrtayloriv