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AMDKFD Code Updated For Linux 4.14, More Changes Being Upstreamed

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  • #11
    Originally posted by bridgman View Post
    amdkfd provides a single entry point (/dev/kfd) with access to all GPUs in order to efficiently support a unified virtual address space across all GPUs and easy peer-to-peer addressing from one GPU to others.
    Does this have anything to do with the limit to the max number of GPUs? As far as I recall that is a limitation of BIOSs being 32 bit and not being able to reserve 256 MB of RAM per GPU device (usual 8-9 GPU limit). With EPYC having 128 PCIE 3.0 lanes, will amdkfd/ROCm allow ~16 GPU systems (8 dual GPU cards in a single node) for latency limited peer-to-peer communication? (As is the case with most lattice calculations, where several KB of data need be sent, but as fast as possible).

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    • #12
      As a Kaveri owner, I haven't bothered to spend the time migrating from RADEON to AMDGPU yet, which is what I understand is the "stock" path. However it sounds as if AMDKFD is going to work with AMDGPU, not with RADEON. So if I want shiny, neat stuff like OpenCL-2.x, it sounds like I'll need to be moving from RADEON to AMDGPU. Is there a suggested timeframe or milestone for that, or is it just when I get a round tuit?

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      • #13
        Originally posted by Meteorhead View Post

        Does this have anything to do with the limit to the max number of GPUs? As far as I recall that is a limitation of BIOSs being 32 bit and not being able to reserve 256 MB of RAM per GPU device (usual 8-9 GPU limit). With EPYC having 128 PCIE 3.0 lanes, will amdkfd/ROCm allow ~16 GPU systems (8 dual GPU cards in a single node) for latency limited peer-to-peer communication? (As is the case with most lattice calculations, where several KB of data need be sent, but as fast as possible).
        No. The limit on most systems is the sbios. In most cases they limit the size of PCI(e) bridge aperture to support 32 bit OSes. Server systems often have "large BAR" support which provides a larger aperture to support more and larger PCI BARs. The number of PCIe lanes is a concern for bandwidth, but generally won't prevent use of the devices.

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        • #14
          Originally posted by phred14 View Post
          As a Kaveri owner, I haven't bothered to spend the time migrating from RADEON to AMDGPU yet, which is what I understand is the "stock" path. However it sounds as if AMDKFD is going to work with AMDGPU, not with RADEON. So if I want shiny, neat stuff like OpenCL-2.x, it sounds like I'll need to be moving from RADEON to AMDGPU.
          Note that the same is true already if you want to use Vulkan.

          Is there a suggested timeframe or milestone for that, or is it just when I get a round tuit?
          We're planning to switch the upstream Linux kernel default for CIK GPUs such as Kaveri from radeon to amdgpu when DC lands upstream, at which point amdgpu will have feature parity with radeon (currently amdgpu has no HDMI/DP audio support for CIK). In the meantime, as of kernel 4.13 you can easily try out the amdgpu driver via

          radeon.cik_support=0 amdgpu.cik_support=1

          on the kernel command line.

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          • #15
            Originally posted by MrCooper View Post
            We're planning to switch the upstream Linux kernel default for CIK GPUs such as Kaveri from radeon to amdgpu when DC lands upstream, at which point amdgpu will have feature parity with radeon (currently amdgpu has no HDMI/DP audio support for CIK).
            Awesome. At this time, does CIK have working UVD/VCE support, and is it just SI that's lacking it (my recollection could be outdated, or that could be part of DC that I haven't tried yet)?

            I'm still running a 7850/Pitcairn in my Ryzen system, and I'm jealous of all the new ROCm stuff I don't get to play with until I upgrade to something newer.

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            • #16
              Originally posted by Veerappan View Post

              At this time, does CIK have working UVD/VCE support, and is it just SI that's lacking it (my recollection could be outdated, or that could be part of DC that I haven't tried yet)?
              CIK has UVD/VCE, but no HDMI/DP audio (needs DC).

              SI has HDMI/DP audio (even without DC), but no UVD/VCE.

              Those are the main blockers for making amdgpu the default for them.

              I'm still running a 7850/Pitcairn in my Ryzen system, and I'm jealous of all the new ROCm stuff I don't get to play with until I upgrade to something newer.
              Not sure Pitcairn can usefully support ROCm.

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