RFD 1128 details: the apparatus, and what each number would mean
The instrument is the card we have, and it is enough for this
An RTX 3090: 24 GB, sm_86, 2020. It is not a 4090, and there is no high-performance inference pipeline on this desk. The machine also carries a Radeon 780M, which is an integrated RDNA3 part sharing system memory with no dedicated VRAM, so it is not a second candidate.
Neither fact blocks this measurement, because tolerance is not a throughput question. It needs enough memory to hold two forms of one stage at once, and it needs identical inputs. 24 GB gives the first and a deterministic renderer gives the second.
Windows reports the 3090 as 4 GB through Win32_VideoController. That is the 32-bit AdapterRAM field overflowing; nvidia-smi reports 24576 MiB. The wrong number is recorded here so nobody re-derives it.
What is compared, and against what
| run | precision | purpose |
|---|---|---|
| A | bf16 | the baseline, on this card, not a paper |
| B | four-bit, DFC host emulation | what the device would compute |
Same image, same seed, same fov in radians. render_view.py is bit-reproducible at one thread: two runs, identical sha256, measured.
The quantity
Surface deviation between the two meshes, in millimetres, paired with a household object. A penny is 1.52 mm and a credit card is 0.76 mm, so half a penny of error is a sentence somebody can act on, and “the mesh looks fine” is not.
Report a distribution rather than one number: median, 95th percentile and maximum. A mean hides the case that matters, which is a hand or an ear moving while the torso stays put.
What would make this a failure
No threshold is set here, on purpose. The RFD that consumes the mesh should set it. What this produces is the number a threshold can be written against.
Why the DFC and not bitsandbytes
A general quantiser measures a four-bit. The device runs the Dataflow Compiler’s four-bit, with its own calibration and layer rules, and the DFC ships a host emulator that runs that graph. The emulator is slow and exact, which is the right trade when the question is numerics rather than speed. weftspun-hailo-dfc:5.3.0 is the image, built and verified importable on 2026-08-22.