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Is there a way to determine the speed of the PCI Express connection to a specific card? I have three cards plugged in:

two Nvidia GTX 480's (one at x16 & and one at x8) one Nvidia GTX 460 running at x8

Is there some way, either by a function call in C or an option to lspci that I can determine the bus speed of the graphics cards? When I only use one of the cards for my CUDA program, I'd like to use the one which is running at x16.

Thanks!

Note: lspci -vvv dumps out

For the two GTX 480s. I don't see any differences that pertain to bus speed.

03:00.0 VGA compatible controller: nVidia Corporation Device 06c0 (rev a3)
        Subsystem: eVga.com. Corp. Device 1480
        Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
        Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
        Latency: 0
        Interrupt: pin A routed to IRQ 16
        Region 0: Memory at d4000000 (32-bit, non-prefetchable) [size=32M]
        Region 1: Memory at b0000000 (64-bit, prefetchable) [size=128M]
        Region 3: Memory at bc000000 (64-bit, prefetchable) [size=64M]
        Region 5: I/O ports at df00 [disabled] [size=128]
        [virtual] Expansion ROM at b8000000 [disabled] [size=512K]
        Capabilities: <access denied>
        Kernel driver in use: nvidia
        Kernel modules: nvidia, nvidiafb, nouveau

03:00.1 Audio device: nVidia Corporation Device 0be5 (rev a1)
        Subsystem: eVga.com. Corp. Device 1480
        Control: I/O- Mem- BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
        Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
        Interrupt: pin B routed to IRQ 5
        Region 0: [virtual] Memory at d7ffc000 (32-bit, non-prefetchable) [disabled] [size=16K]
        Capabilities: <access denied>

04:00.0 VGA compatible controller: nVidia Corporation Device 06c0 (rev a3)
        Subsystem: eVga.com. Corp. Device 1480
        Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
        Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
        Latency: 0
        Interrupt: pin A routed to IRQ 16
        Region 0: Memory at dc000000 (32-bit, non-prefetchable) [size=32M]
        Region 1: Memory at c0000000 (64-bit, prefetchable) [size=128M]
        Region 3: Memory at cc000000 (64-bit, prefetchable) [size=64M]
        Region 5: I/O ports at cf00 [size=128]
        [virtual] Expansion ROM at c8000000 [disabled] [size=512K]
        Capabilities: <access denied>
        Kernel driver in use: nvidia
        Kernel modules: nvidia, nvidiafb, nouveau

04:00.1 Audio device: nVidia Corporation Device 0be5 (rev a1)
        Subsystem: eVga.com. Corp. Device 1480
        Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
        Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
        Latency: 0, Cache Line Size: 64 bytes
        Interrupt: pin B routed to IRQ 5
        Region 0: Memory at dfffc000 (32-bit, non-prefetchable) [size=16K]
        Capabilities: <access denied>

And the only differences I see relate specifically to the memory mapping:

myComputer:~> diff card1 card2
3c3
< Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
---
> Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
7,11c7,11
< Region 0: Memory at d4000000 (32-bit, non-prefetchable) [size=32M]
< Region 1: Memory at b0000000 (64-bit, prefetchable) [size=128M]
< Region 3: Memory at bc000000 (64-bit, prefetchable) [size=64M]
< Region 5: I/O ports at df00 [disabled] [size=128]
< [virtual] Expansion ROM at b8000000 [disabled] [size=512K]
---
> Region 0: Memory at dc000000 (32-bit, non-prefetchable) [size=32M]
> Region 1: Memory at c0000000 (64-bit, prefetchable) [size=128M]
> Region 3: Memory at cc000000 (64-bit, prefetchable) [size=64M]
> Region 5: I/O ports at cf00 [size=128]
> [virtual] Expansion ROM at c8000000 [disabled] [size=512K]
18c18
< Control: I/O- Mem- BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
---
> Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
19a20
> Latency: 0, Cache Line Size: 64 bytes
21c22
< Region 0: [virtual] Memory at d7ffc000 (32-bit, non-prefetchable) [disabled] [size=16K]
---
> Region 0: Memory at dfffc000 (32-bit, non-prefetchable) [size=16K]
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1 Answer 1

up vote 1 down vote accepted

I tried this: cat /var/log/Xorg.0.log | grep "NVIDIA"

It will show you the cards and in what PCI Express slot they are and what is the width of that Slot. For example:

20.502] (II) NVIDIA(0): NVIDIA GPU GeForce 9500 GT (G96) at PCI:1:0:0 (GPU-0)
[ 20.502] (--) NVIDIA(0): Memory: 1048576 kBytes
[ 20.502] (--) NVIDIA(0): VideoBIOS: 62.94.1f.00.8a
[ 20.502] (II) NVIDIA(0): Detected PCI Express Link width: 16X
[ 20.502] (--) NVIDIA(0): Interlaced video modes are supported on this GPU
[ 20.502] (--) NVIDIA(0): Connected display device(s) on GeForce 9500 GT at PCI:1:0:0
[ 20.502] (--) NVIDIA(0): Samsung SyncMaster (CRT-1)
[ 20.502] (--) NVIDIA(0): Samsung SyncMaster (CRT-1): 400.0 MHz maximum pixel clock

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