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Thread: Graphics ram detection

  1. #1
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    Default Graphics ram detection

    [drm] Detected VRAM RAM=256M, BAR=256M
    [drm] RAM width 64bits DDR
    [TTM] Zone kernel: Available graphics memory: 1028294 kiB.
    [drm] radeon: 256M of VRAM memory ready
    [drm] radeon: 512M of GTT memory ready.
    These conflicting messages confuse me. The card has 512mb of ram, and this is 2.6.33 so it's expected to only be able to use 256mb, but why the heck does it claim to have 1gb?

  2. #2
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    There's no mention of "Hypermemory" or any of that crap on the box.

  3. #3
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    A kernel guru please chime in

    From the code it looks like it's just total ram/2. But why would TTM use system ram, when there's so much graphics ram?

  4. #4
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    when your GPU memory is full, textures are kept in system memory and will be pushed to your GPU on demand. Sometimes buffers need to be moved to main memory for CPU drawing operations. Etc..

  5. #5
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    OK, then why is there only one TTM zone/pool?

    Or is GTT (what does it mean? Google isn't helpful) the TTM zone in gpu vram?

  6. #6
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    Well, found an Intel whitepaper from 2005 explaining GTT. Graphics Translation Table, for TLB mapping graphics ram to address space.

    Thread closed :P

  7. #7
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    The GPU has the ability to access system pages directly via a address remapping table (GART). This is provided by the northbridge in the case of AGP or by the GPU directly for non-AGP. The GTT size is the max amount of system pages that can be mapped into the GPU's address space. Note that pages are bound as needed, so the system pages are not "wasted" so to speak.

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