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Thread: 5870 and pciexpress2.0

  1. #1
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    Default 5870 and pciexpress2.0

    I have ubuntu 10.10 with 2.6.38 kernel and radeon drivers from xorg-edgers ppa.

    Works fine except lspci reports 2.5 GT/s for both LinkCap and LinkSta, instead of 5GT/s , which is normal for pcie 2.0 (in windows it works in v2.0 mode fine).

    Even checked bits in pci config space, 0x64 and 0x6a reports mode for this card (cap and state), 01 - 2.5 GT/s, 02 - 5 GT/s, I have both - 01

    Why is it so?

  2. #2
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    Quote Originally Posted by netkas View Post
    I have ubuntu 10.10 with 2.6.38 kernel and radeon drivers from xorg-edgers ppa.

    Works fine except lspci reports 2.5 GT/s for both LinkCap and LinkSta, instead of 5GT/s , which is normal for pcie 2.0 (in windows it works in v2.0 mode fine).

    Even checked bits in pci config space, 0x64 and 0x6a reports mode for this card (cap and state), 01 - 2.5 GT/s, 02 - 5 GT/s, I have both - 01

    Why is it so?
    I don't think PCIE 2.0 is enabled by default with the open drivers right now. Alex enabled it a couple of months ago but it caused problems on some systems so IIRC he disabled it.

  3. #3
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    could you by any chance point to that commit or some hints to find it ?

  4. #4
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    found it in kernel in evergreen.c

  5. #5
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    Given the bottlenecks on r600c/g (starving GPU of data on state change), I doubt PCI-e 2.0 will make a noticeable difference, if any. Someone correct me if I'm wrong there.

  6. #6
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    Quote Originally Posted by DanL View Post
    Given the bottlenecks on r600c/g (starving GPU of data on state change), I doubt PCI-e 2.0 will make a noticeable difference, if any. Someone correct me if I'm wrong there.
    it has nothing do to with the subject tho.

    afai discovered, linux just uses what bios set, two my cards boots with 5.0 gt/s mode (8800gt/gtx285, not using nvidia blob), other, gtx480/5870/4850 boots in 2.5 gt/s mode

  7. #7
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    Still, would be interesting to see a bench on whether double the bandwidth helps r600g.

  8. #8
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    Quote Originally Posted by netkas View Post
    it has nothing do to with the subject tho
    Sure it does. If you're bottlenecked in one place, then worrying about making a wider path further down the stream is pointless.

    Still, would be interesting to see a bench on whether double the bandwidth helps r600g.
    I would attempt it, but I don't think my lowly RadeonHD 4550 card is the right tool for the job :\

  9. #9
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    Quote Originally Posted by DanL View Post
    Sure it does. If you're bottlenecked in one place, then worrying about making a wider path further down the stream is pointless.



    I would attempt it, but I don't think my lowly RadeonHD 4550 card is the right tool for the job :\
    Just think about future, once we have opencl state tracker this (pcie speed) will come in play.

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