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Comment by theandrewbailey | Hacker News Reader

> The graphics card has already been demonstrated rendering a raw 8K video – the initial demo showed this running at 17 frames per second, and switching to the SSG, that was boosted to over 90 frames per second.

I doubt that the same GPU was used. If it is, we're in trouble (or have unoptimized software). I thought that someone would have already solved the "let's stream data in and out and not interrupt whatever the GPU is doing" problem, but meanwhile many people are fretting over what PCIe version (thus, attained speeds) they can use.

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One frame of uncompressed 48bit color 8k video is 190MB. So just sending it through ideal pcie 3.0 16x you're limited to 83fps. Add overhead, latencies, actual transfer slower than theoretical, and especially actual processing requiring several frames at once. 17fps seems good, considering.

Indeed modern GPUs do copies over the bus while executing shaders/kernels. But once you saturate the bus, you are limited in how much shader execution you can accomplish as a result. If this scene required more textures than fit in memory, it would benefit from having a local DDR-accessible cache instead of having to grab it over PCIe.

I agree, but...

A GPU's 16 lanes of PCIe 3.0 provide almost 16 GB/s of bandwidth. An M.2 SSD (used in this card) is at best 4 GB/s (PCIe 3.0 x4 lanes). This card has two M.2 slots.

Even at those speeds, accessing data from system RAM is faster. (depends on specifics, but system RAM is easily 40+ GB/s) How does increasing data bandwidth 50% increase performance by 4? Are inefficiencies (and latencies) really eating up all that?

> "let's stream data in and out and not interrupt whatever the GPU is doing"

You're quoting this but I'm not sure I understand what problem you're referencing. Streaming data to the GPU isn't a problem of interrupting it. GPUs use memory fences, atomics, and other things you might find in CPU land. Why are we in trouble if the demo was true? For every type of hardware, I can come up with a rendering algorithm and data set that makes it look better than similar hardware in a different configuration. If you have more memory bandwidth, you should be using it accordingly.

What does "interrupt" mean here? If you don't have video data available to the card fast enough, it's not going to have anything to render.

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