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AMD Lands A Number Of RadeonSI RDNA NGG Fixes Ahead Of RDNA3 Enabling

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  • AMD Lands A Number Of RadeonSI RDNA NGG Fixes Ahead Of RDNA3 Enabling

    Phoronix: AMD Lands A Number Of RadeonSI RDNA NGG Fixes Ahead Of RDNA3 Enabling

    Well known AMD Mesa developer Marek Olšák landed more than two dozen patches this weekend fixing up Next-Gen Geometry (NGG) Stream-Out / Transform Feedback functionality for RDNA/RDNA2 GPUs ahead of the NGG Stream-Out enabling for upcoming RDNA3 graphics cards...

    https://www.phoronix.com/scan.php?pa...ream-Out-Fixes

  • #2
    Not technically related to this, but I heard that recently the Windows driver for RDNA2 cards got a considerable uplift in OpenGL performance. Is this something we've been already enjoying with the Linux driver, will be coming soon, or is yet to be implemented?

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    • #3
      Is there still a chance to see NGG working (with reasonable benefits) on Vega?

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      • #4
        ms178

        Asking myself the same, I briefly read the AMDVLK PAL code a few years back. IIRC and according to the code comments, there are several hardware bugs prohibiting this. The issues range from GPU hangs, to signals for synchronization not being delivered, work items being skipped and some low level memory management related stuff.

        There was also an interface regarding special gds allocations missing in the kernel module and libdrm - that might still be the case for GFX9. It is likely that the implementation has also changed with RDNA 1/2/3 and the HW registers regarding NGG on Vega aren't really documented, so its not even guaranteed that the code can be backported to Vega hardware.

        I dunno if it's even possible to work around all of that, but it seems like there would be so much overhead associated with mitigating this, that the performance gains would be negligible and even negative in some cases.

        Just push core and memory clocks as fast as you can while staying within a reasonable power target. It helps fixed function performance (i.e. geometry throughput) quite a bit.
        Last edited by kiffmet; 12 June 2022, 07:55 AM.

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        • #5
          Originally posted by ms178 View Post
          Is there still a chance to see NGG working (with reasonable benefits) on Vega?
          No, it's totally different and it would be slower.

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          • #6
            Originally posted by marek View Post

            No, it's totally different and it would be slower.
            What about driver-level FSR for AMDGPU or generically into Mesa?

            That's the one thing I've been wanting to ask someone who are so wise in the way of graphics.

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            • #7
              Another thing I want to ask the AMD driver people: are there any changes specifically for the upcoming multi-chip GPUs?


              This seems like a natural fit for tiled rendering, especially with AMD's cache-heavy setup... but that's not how the current GPU drivers work, right?

              Or do they already work that way?

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              • #8
                NGG stream-out for RADV was challenging too but seems to have stabilized as well since its wiring up three years ago.
                This is inaccurate. We removed NGG streamout functionality from RADV last year, for two reasons:
                • It was never stable enough to be enabled by default
                • It was LLVM only, we'll need to port it to NIR instead

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                • #9
                  Can someone explain what NGG is? Couldn't really find something in the internet. All links pointed to Phoronix which doesn't really explain what this is.

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                  • #10
                    Originally posted by skeevy420 View Post

                    What about driver-level FSR for AMDGPU or generically into Mesa?
                    Not at the moment, though it would be possible since it's open source, though different between Mesa GL and Mesa Vulkan.

                    Originally posted by brucethemoose View Post
                    Another thing I want to ask the AMD driver people: are there any changes specifically for the upcoming multi-chip GPUs?
                    No comment regarding future chips.

                    Originally posted by Steffo View Post
                    Can someone explain what NGG is? Couldn't really find something in the internet. All links pointed to Phoronix which doesn't really explain what this is.
                    NGG was a rewrite of the geometry pipeline in hw. NGG stands for next generation graphics, referring to mesh shaders and the rewrite. It's talked about only because the hw has (had) both the old and new pipeline and driver developers constantly talk about which one to use, but being aware of it is not useful to the general public.

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