d4r/docs/performance.md

Performance

Unless stated otherwise, the frame rates and kernel timings on this page were measured on an RX 7700 XT (gfx1101). Native FP8 changes both arithmetic and cost, so the gfx11 results cannot be projected to RDNA4; the one RDNA4 measurement is in RDNA4. No RDNA4 game frame rate has been measured.

Method

• Hardware and settings: Radeon RX 7700 XT (RDNA3, 54 CUs), Ryzen 9 5900XT, Linux 6.18. SILENT HILL Townfall at 2560×1440 output.
• Route: every run plays the same scripted 62-second walk through a street, with fog, wires, fences and signage.
• Frame rate: from MangoHud's per-frame log over the walk, as frames divided by the sum of frame times.
• Pairing: runs are compared back-to-back in one session, because repeated runs of an identical setup vary by about 1%.
• Screen recording: it costs a few fps, so recorded videos show slightly lower numbers than the table.
• Latency: all DLSS numbers are same-frame (frame age 0). Every frame shows its own DLSS result, as with a native upscaler.
• 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.

Results

Mode (render resolution)	DLSS 3 CNN (E)	DLSS 4 (K)	DLSS 4.5 (M)	FSR 4*
Quality (1705×960)	71.7	67.9	49.3	76.0
Balanced (1488×837)	80.8	75.9	58.0	84.5
Performance (1280×720)	89.7	84.1	69.0	94.0
Ultra Performance (853×480)	89.1	95.5	92.2	107.3
Native 2560×1440, no upscaling (TSR at 100%)		49.1

* 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).

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.

What each step contributed

DLSS 4 (K) at Quality, frames per second on the walk:

Step	fps
ZLUDA only: the transformer's outputs were non-finite, so the network had no effect	58.5*
All eleven K layers native	65.0*
Wide deep layers, f32 accumulation, cheaper operand transposes	66.0
NGX's CPU syncs removed, faster marker polling, no sync before the output copy	66.7
DLSS queued behind a GPU-side wait for the inputs (GPU busy 95% → 99%)	68.0
Native output kernel writes the game-side buffer directly	68.4
NGX samples the input buffers in place (no array copies)	69.4

* Measured from the shim's frame log on a similar stretch, before the MangoHud method was in use.

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.

DLSS 4 (K) tuning round, 2026-10-04

A separate work copy of this tree tuned the K kernels with byte-identical output (see 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:

	shipped	tuned
2560×1440 Quality: DLSS GPU time (gpu_eval)	2.89 ms	2.41 ms
1920×1080 Quality: DLSS GPU time	1.86 ms	1.50 ms
2560×1440 Quality: sum of kernels	2.90 ms	2.40 ms

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%).

These were measured in the work copy. They have not been re-measured from this repository since the port.

What did not help

• Accumulating in f16 on the WMMA units. The error grows about 20× and the image degrades.
• Occupancy tweaks (VGPR caps, waves-per-EU hints) and persistent work-groups.
• Non-temporal hints for activation traffic.
• Splitting the position-only layers by channel instead of by token. It halves weight traffic but serialises the compute.
• Mapping the Vulkan buffers directly as HIP arrays. ROCm 7.2 does not export hipExternalMemoryGetMappedMipmappedArray.
• 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.

Where the time goes now

For DLSS 4 at Quality the GPU spends about 2.8 ms per frame in DLSS kernels:

• NVIDIA's output kernel: 0.82 ms. It is ALU-bound at close to the GPU's instruction rate.
• The eleven network layers: 1.6 ms.
• The input kernel, exposure and miscellaneous kernels: about 0.35 ms.

The game-side input and output copies add about 0.3 ms. native-kernels.md lists every kernel.

RDNA4

DLSS 4.5 (M) on an RX 9070 XT (gfx1201, native FP8, fast set), 1280×720 → 3840×2160 in the D3D12 harness with DLSS 310.7. Median GPU time per frame in milliseconds, from D4R_CUDA_KERNEL_PROFILE (frames 21–40); "before" is the same texture set with the previous Swin layers.

Kernel	before	now
enc3 tube (6 launches)	1.50	0.52
enc1	1.32	0.33
dec1	0.94	0.33
post (texture kernel)	0.67	0.68
enc2	0.51	0.19
dec2	0.50	0.17
downsample (texture kernel, now wave64)	0.36	0.34
dec0, enc0 (texture kernels)	0.18, 0.13	0.18, 0.13
total	6.10	2.86

With NativeFp8 off the same card runs the layers as 16-bit math, which never re-encoded its operands: that set takes 3.37 ms here (5.94 ms at 1920×1080 → 3840×2160, against 4.63 ms for the FP8 set). So against a 9070 XT that was already running with NativeFp8 off, the FP8 set is about 15% faster at 1280×720 and 22% at 1920×1080, not twice as fast. In Ghost of Tsushima at 1920×1080 → 3840×2160 the upscaler time shown in game went from 7.0 ms (16-bit set) to 5.8 ms (this FP8 set).

The shim's whole-evaluation GPU time (D4R_PROFILE, no per-kernel synchronisation) went from 5.9–6.0 ms to 2.80 ms with the harness's 200 ms pause between frames, and to 2.39–2.43 ms with frames 0–4 ms apart (2000 frames at 4 ms spacing: median 2.39, maximum 2.56). The difference is the driver's clock governor: with the 200 ms pause the GPU is about 9% busy and runs at about 2790 MHz, with frames 0–4 ms apart it is 80–98% busy and runs at 3180–3300 MHz, as it does under a game's rendering load. Other GPU users on the desktop add occasional slower frames to any of these figures; the previous kernels show the same disturbances.

The change is in native-kernels.md: the FP8 layers keep their activations as e4m3 bytes, and the downsample kernel is built as wave64 on gfx12. The output image is byte-identical before and after.