ayo
22026ede12
Preset K, byte-identical to the previous output in all captured buffers and the harness image, measured on an RX 7700 XT: - LDS row padding so WMMA operand loads hit distinct banks - WGP mode for enc1/enc2/dec1/dec2, ds_bpermute half-wave exchange for enc0/dec0/dec3, more waves per window in enc4/dec4/dec5 - cheaper operand plumbing in common/wmma_layout.h (packed f16 conversions, no dynamic vector indexing), raw buffer weight loads, accumulator-init vectors prepared once - enc1 as a single-buffer recompute layer, dec1 Q/K/V chains split - dec5 as four dependent phase kernels
78 lines
5.3 KiB
Markdown
78 lines
5.3 KiB
Markdown
# Performance
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All frame rates and kernel timings on this page were measured on an RX 7700 XT (gfx1101). RDNA4 (gfx1200/gfx1201) has compile and emulator validation only; no RDNA4 frame rate, latency, or kernel timing has been measured. Native FP8 may change both arithmetic and cost, so the gfx11 results cannot be projected to it.
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## Method
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- **Hardware and settings:** Radeon RX 7700 XT (RDNA3, 54 CUs), Ryzen 9 5900XT, Linux 6.18. SILENT HILL Townfall at 2560×1440 output.
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- **Route:** every run plays the same scripted 62-second walk through a street, with fog, wires, fences and signage.
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- **Frame rate:** from MangoHud's per-frame log over the walk, as frames divided by the sum of frame times.
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- **Pairing:** runs are compared back-to-back in one session, because repeated runs of an identical setup vary by about 1%.
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- **Screen recording:** it costs a few fps, so recorded videos show slightly lower numbers than the table.
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- **Latency:** all DLSS numbers are same-frame (frame age 0). Every frame shows its own DLSS result, as with a native upscaler.
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- **Upscaler modes:** every mode uses OptiScaler's render-ratio override (1.5, 1.72, 2.0, 3.0), so the result does not depend on the DLSS mode chosen in the game.
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## Results
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| Mode (render resolution) | DLSS 3 CNN (E) | DLSS 4 (K) | DLSS 4.5 (M) | FSR 4\* |
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| Quality (1705×960) | **71.7** | 67.9 | 49.3 | 76.0 |
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| Balanced (1488×837) | **80.8** | 75.9 | 58.0 | 84.5 |
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| Performance (1280×720) | **89.7** | 84.1 | 69.0 | 94.0 |
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| Ultra Performance (853×480) | 89.1 | **95.5** | 92.2 | 107.3 |
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| Native 2560×1440, no upscaling (TSR at 100%) | | 49.1 | | |
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\* FSR 4 and the native row are from 2026-09-27; the DLSS columns from 2026-09-29, when the machine ran about 2–4% slower overall (release 0.1.1 at Quality that day: E 71.2, K 67.9, M 48.4 fps, against 72.4, 69.4 and 51.5 two days earlier). The render resolution of every mode is set with OptiScaler's ratio override for whichever DLSS mode the game is set to (ratios 1.5, 1.72, 2.0 and 3.0).
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DLSS 4's cost is almost constant across modes (about 2.8 ms of GPU time per frame). Its network runs on a grid set by the output resolution, not the render resolution, so the gap to FSR 4 widens as the render resolution drops. The CNN gets more expensive at the 3× ratio, so K is the better choice at Ultra Performance.
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## What each step contributed
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DLSS 4 (K) at Quality, frames per second on the walk:
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| Step | fps |
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| ZLUDA only: the transformer's outputs were non-finite, so the network had no effect | 58.5\* |
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| All eleven K layers native | 65.0\* |
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| Wide deep layers, f32 accumulation, cheaper operand transposes | 66.0 |
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| NGX's CPU syncs removed, faster marker polling, no sync before the output copy | 66.7 |
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| DLSS queued behind a GPU-side wait for the inputs (GPU busy 95% → 99%) | 68.0 |
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| Native output kernel writes the game-side buffer directly | 68.4 |
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| NGX samples the input buffers in place (no array copies) | 69.4 |
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\* Measured from the shim's frame log on a similar stretch, before the MangoHud method was in use.
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DLSS 4.5 (M) at Quality went from 28 fps (ZLUDA only) to 42 with the first native Swin layers, 46 with more waves per window, 50 with fast numerics and the texture-kernel tails, and 51.5 with the hand-off changes.
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## DLSS 4 (K) tuning round, 2026-10-04
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A separate work copy of this tree tuned the K kernels with byte-identical output (see [native-kernels.md](native-kernels.md)). Numbers from that copy, RX 7700 XT, D3D12 harness, motion scene, FrameAge 0, warmed medians of back-to-back runs; the shipped 0.1.4 kernels against the tuned set:
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| | shipped | tuned |
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| 2560×1440 Quality: DLSS GPU time (`gpu_eval`) | 2.89 ms | 2.41 ms |
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| 1920×1080 Quality: DLSS GPU time | 1.86 ms | 1.50 ms |
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| 2560×1440 Quality: sum of kernels | 2.90 ms | 2.40 ms |
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In SILENT HILL Townfall (static scene, K Quality 1706×960 → 2560×1440, MangoHud, two alternating rounds): 63.1 / 63.3 fps → 65.4 / 65.1 fps with default settings (frame time −0.5 ms), DLSS GPU time 2.92 → 2.41 ms. At 1920×1080: 86.1 → 89.3 fps. DLSS 4.5 (M) gained little from its own round (DLSS GPU time 7.96 → 7.91 ms at 2560×1440 Quality, Townfall 1080p +0.7%).
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These were measured in the work copy. They have not been re-measured from this repository since the port.
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## What did not help
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- **Accumulating in f16 on the WMMA units.** The error grows about 20× and the image degrades.
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- **Occupancy tweaks** (VGPR caps, waves-per-EU hints) and **persistent work-groups.**
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- **Non-temporal hints** for activation traffic.
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- **Splitting the position-only layers by channel** instead of by token. It halves weight traffic but serialises the compute.
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- **Mapping the Vulkan buffers directly as HIP arrays.** ROCm 7.2 does not export `hipExternalMemoryGetMappedMipmappedArray`.
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- **Signalling the game's Vulkan timeline semaphore from HIP.** HIP does not import timeline semaphores, so the end of DLSS is still signalled from the CPU.
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## Where the time goes now
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For DLSS 4 at Quality the GPU spends about 2.8 ms per frame in DLSS kernels:
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- NVIDIA's output kernel: 0.82 ms. It is ALU-bound at close to the GPU's instruction rate.
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- The eleven network layers: 1.6 ms.
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- The input kernel, exposure and miscellaneous kernels: about 0.35 ms.
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The game-side input and output copies add about 0.3 ms. [native-kernels.md](native-kernels.md) lists every kernel.
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