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  • #16
    Originally posted by robclark View Post
    well, the gpu is still not synchronous, but the symantics of glTexImage are synchronous. So you either need a copy there, or some GL extension that lets the driver hold on to those pages until some time after.

    Also, frequently drivers will convert the texture into some internal tiled format for better memory access efficiency. Which at least makes sense if you are going to use the texture multiple times.
    Huh.. that's a bit of a shock to be honest. I was always under the impression that such memory had to be uploaded into VRAM (via memcpy'ing into mapped memory regions I presumed) to be accessible to the GPU. Or am I misunderstanding something?

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    • #17
      Originally posted by Ancurio View Post
      Huh.. that's a bit of a shock to be honest. I was always under the impression that such memory had to be uploaded into VRAM (via memcpy'ing into mapped memory regions I presumed) to be accessible to the GPU. Or am I misunderstanding something?
      operating from VRAM is much faster for a gpu than operating from system ram.. so for one time use, it might be more overhead to transfer from system memory to video memory, but if you know you are going to use that data multiple times, you probably want it in VRAM.

      Jerome's proposal should actually make it possible to migrate pages to VRAM (and then migrate back to system memory on CPU page fault from accessing pages that were previously migrated to VRAM). Obviously you don't want a lot of thrashing because moving things back and forth between system memory and video memory can defeat the advantages of operating from video memory.

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      • #18
        Originally posted by robclark View Post
        operating from VRAM is much faster for a gpu than operating from system ram.. so for one time use, it might be more overhead to transfer from system memory to video memory, but if you know you are going to use that data multiple times, you probably want it in VRAM.

        Jerome's proposal should actually make it possible to migrate pages to VRAM (and then migrate back to system memory on CPU page fault from accessing pages that were previously migrated to VRAM). Obviously you don't want a lot of thrashing because moving things back and forth between system memory and video memory can defeat the advantages of operating from video memory.
        Ah, I see, it's no black and white situation with memory access. This makes sense. Thanks for the explanation!

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