5 ms·

I think much of the difficulty is just that, for example, the 1.8 TB/s of an RTX 5090 is a lot of bandwidth for a game to use. That's over 50,000 4k textures pe

by nearbuy 4mo ago

I think much of the difficulty is just that, for example, the 1.8 TB/s of an RTX 5090 is a lot of bandwidth for a game to use. That's over 50,000 4k textures per second at 32bpp.

gmueckl 4mo ago
That sounds like a lot, but: modern renderers do between 20 to 40 passes, many of them in screen space. And each screen space pass typically reads from at least two input images, sometimes 3 or 4 even with optimally packed inputs. At 60fps that can quickly get up to way over 2000 full screen buffer reads per second and more for less than optimal access patterns in some algorithms. That also doesn't account for texture access during shading passes, which are somewhat random memory accesses.
- nearbuy 4mo ago
  Very true, but I'll point out that even those 2000 full screen reads per second at 4k are only 4% of the 5090's bandwidth. Sacrificing some of that speed for a unified memory architecture seems like a good trade. Plus, DLSS can greatly reduce the bandwidth requirements for 4K gaming.
  - gmueckl 4mo ago
    I'm being very, very conservative with my estimates here. Based on the renderers I know, I could have easily tweaked the numbers to go up to 8000 full screen texture reads per second. That doesn't include texture or geometry or BVH reads or any memory writes. That is all in addition to those operations.
    - nearbuy 4mo ago
      But do you think you'll reach 1.8 TB/s?
      - gmueckl 4mo ago
        Quite likely, but the transfer throughput is required in bursts, not necessarily continously. Let me put it this way: what I care about is how quickly data arrives after a bunch of shader threads request it. Throughput is one way for hardware to reduce that time. The other way is to hide the latency (GPUs do a lot to keep themselves busy while waiting for memory), but those strategies can only do so much. Lower memory throughput almost always leads to a longer runtime of GPU calls in practice, and thus lower update rates.
        nearbuy 4mo ago
        Empirically, these benchmarks are showing it doesn't make much difference once you reach this level of bandwidth: https://www.tomshardware.com/pc-components/gpus/early-rtx-5090d-v2-benchmarks-suggest-that-maybe-384-bit-memory-is-just-fine-after-all-nerfed-china-market-gpu-runs-within-2-2-percent-of-5090d-in-some-tests https://www.tomshardware.com/pc-components/gpus/early-rtx-50...
maccard 4mo ago
I agree with you in theory. A couple of points - that’s currently the most experience and high performing card on the market. Most people on steam are using an RTX 3060 which has more like 360GB/s. That’s a factor of 6. How do you design resource usage that scales with that amount of extremity? (We try to, fwiw). That spec is also a throughput measured per second whereas our frame rates are much higher than 1/s. At 60hz, that’s now between 140 and 800 textures a frame. If you miss _one_ you don’t get that back. A single main character in a game can be 2-5 regular textures, plus all of the extra mapping textures we have these days. Now do landscapes, environments, props, background videos, and it all adds up. 4k textures are pretty universally used. If you look at a tiny object up close we need a higher res texture to be able to show it neatly. You also have memory pressure - raytracing makes heavy use of VRAM so you have to make the tradeoff of how much do you want to allocate to caching lighting, vs how much you want to keep textures and geo around. Lastly, as you say, actually keeping up with 360GB/s from the CPU side is tough. If you require any transformation or CPU operations that’s just not going to happen. If you need to pull from disk, even on an NVMe drive reading synchronously, the max throughput is < 10% of that, and that assumes you are actually reading 360GB from disk. If you pause to do anything else, you’ll significantly slow that down. Players also generally don’t like it if we thrash their NVMe disks :)
- nearbuy 4mo ago
  All good points. Absolutely an RTX 3060 is a more normal gamer GPU than the 5090, but you're also not playing in 4k without DLSS on a 3060. Drop to the most common resolution on Steam (1080p), and turn on DLSS and you've basically cancelled out that 6x factor in bandwidth. Even if the 3060 had more bandwidth, it doesn't have enough processing power for native 4k gaming in typical games. So 360 GB/s is still a lot of bandwidth for the resolution most 3060 gamers are using.
  - maccard 4mo ago
    Playing at 1080p doesn’t reduce your texture size, for the most part. You still use those 4k textures because you’re only seeing a subset of the texture projected at a close distance. We’re still using 4k textures for terrain brushes to cover the 6km open worlds. DLSS isn’t just a magic on switch for free perfect up scaling. If you rendered at 720p and DLSS’ed up to 1080 it’s still going to look pretty rubbish.Its always surprising to me just how many people have 1080 monitors though given we’ve had more than that for two generations of consoles. And lastly - all the same points still apply about frame rate (which can be more than 60) and memory bandwidth per frame and cache invalidation etc at 360GB/S, as they do at 1.8TB/s

by nearbuy 4mo ago

I think much of the difficulty is just that, for example, the 1.8 TB/s of an RTX 5090 is a lot of bandwidth for a game to use. That's over 50,000 4k textures per second at 32bpp.

gmueckl 4mo ago

That sounds like a lot, but: modern renderers do between 20 to 40 passes, many of them in screen space. And each screen space pass typically reads from at least two input images, sometimes 3 or 4 even with optimally packed inputs. At 60fps that can quickly get up to way over 2000 full screen buffer reads per second and more for less than optimal access patterns in some algorithms. That also doesn't account for texture access during shading passes, which are somewhat random memory accesses.

nearbuy 4mo ago
Very true, but I'll point out that even those 2000 full screen reads per second at 4k are only 4% of the 5090's bandwidth. Sacrificing some of that speed for a unified memory architecture seems like a good trade. Plus, DLSS can greatly reduce the bandwidth requirements for 4K gaming.
- gmueckl 4mo ago
  I'm being very, very conservative with my estimates here. Based on the renderers I know, I could have easily tweaked the numbers to go up to 8000 full screen texture reads per second. That doesn't include texture or geometry or BVH reads or any memory writes. That is all in addition to those operations.
  - nearbuy 4mo ago
    But do you think you'll reach 1.8 TB/s?
    - gmueckl 4mo ago
      Quite likely, but the transfer throughput is required in bursts, not necessarily continously. Let me put it this way: what I care about is how quickly data arrives after a bunch of shader threads request it. Throughput is one way for hardware to reduce that time. The other way is to hide the latency (GPUs do a lot to keep themselves busy while waiting for memory), but those strategies can only do so much. Lower memory throughput almost always leads to a longer runtime of GPU calls in practice, and thus lower update rates.
      - nearbuy 4mo ago
        Empirically, these benchmarks are showing it doesn't make much difference once you reach this level of bandwidth: https://www.tomshardware.com/pc-components/gpus/early-rtx-5090d-v2-benchmarks-suggest-that-maybe-384-bit-memory-is-just-fine-after-all-nerfed-china-market-gpu-runs-within-2-2-percent-of-5090d-in-some-tests https://www.tomshardware.com/pc-components/gpus/early-rtx-50...

maccard 4mo ago

I agree with you in theory. A couple of points - that’s currently the most experience and high performing card on the market. Most people on steam are using an RTX 3060 which has more like 360GB/s. That’s a factor of 6. How do you design resource usage that scales with that amount of extremity? (We try to, fwiw). That spec is also a throughput measured per second whereas our frame rates are much higher than 1/s. At 60hz, that’s now between 140 and 800 textures a frame. If you miss _one_ you don’t get that back. A single main character in a game can be 2-5 regular textures, plus all of the extra mapping textures we have these days. Now do landscapes, environments, props, background videos, and it all adds up. 4k textures are pretty universally used. If you look at a tiny object up close we need a higher res texture to be able to show it neatly. You also have memory pressure - raytracing makes heavy use of VRAM so you have to make the tradeoff of how much do you want to allocate to caching lighting, vs how much you want to keep textures and geo around. Lastly, as you say, actually keeping up with 360GB/s from the CPU side is tough. If you require any transformation or CPU operations that’s just not going to happen. If you need to pull from disk, even on an NVMe drive reading synchronously, the max throughput is < 10% of that, and that assumes you are actually reading 360GB from disk. If you pause to do anything else, you’ll significantly slow that down. Players also generally don’t like it if we thrash their NVMe disks :)

nearbuy 4mo ago
All good points. Absolutely an RTX 3060 is a more normal gamer GPU than the 5090, but you're also not playing in 4k without DLSS on a 3060. Drop to the most common resolution on Steam (1080p), and turn on DLSS and you've basically cancelled out that 6x factor in bandwidth. Even if the 3060 had more bandwidth, it doesn't have enough processing power for native 4k gaming in typical games. So 360 GB/s is still a lot of bandwidth for the resolution most 3060 gamers are using.
- maccard 4mo ago
  Playing at 1080p doesn’t reduce your texture size, for the most part. You still use those 4k textures because you’re only seeing a subset of the texture projected at a close distance. We’re still using 4k textures for terrain brushes to cover the 6km open worlds. DLSS isn’t just a magic on switch for free perfect up scaling. If you rendered at 720p and DLSS’ed up to 1080 it’s still going to look pretty rubbish.Its always surprising to me just how many people have 1080 monitors though given we’ve had more than that for two generations of consoles. And lastly - all the same points still apply about frame rate (which can be more than 60) and memory bandwidth per frame and cache invalidation etc at 360GB/S, as they do at 1.8TB/s