Two 5090 owners hit `--kv-cache-dtype nvfp4 requires sm100f` crashing
mid-boot on the #246 A/B (disc #571). Root-caused from vLLM #43562 /
TRT-LLM #10241: nvfp4 KV forces the trtllm-gen FP4 FMHA, built ONLY for
datacenter Blackwell sm_100/sm_103. Consumer Blackwell (sm_120/121 —
RTX 5090 / PRO 6000 Blackwell) is a HIGHER cc number but a different
family with no FMHA build. NVFP4 *weights* work there; only the KV path
doesn't. Our #246 gate had used a numeric ">=10.0" floor that wrongly
passed sm_120 — a floor can't express "sm_100/103 but not the
numerically-higher sm_120".
- gates.py: new `_ARCH_KERNEL_SM_FAMILY` allowlist ({nvfp4: sm_100/103});
dropped nvfp4 from the numeric `_ARCH_KERNEL_SM` floor; family-membership
reject with the FMHA reason + fp8_e4m3 fallback.
- arch-ab.sh: nvfp4 arm now refuses on consumer Blackwell (not just
<sm_10), naming the FMHA gap + the fp8_e4m3 path; dropped nvfp4 from the
recommended arms in help.
- hardware profiles: removed nvfp4 from rtx-5090 / rtx-6000-pro-blackwell
KV lists (both sm_120) + added a why-not note.
- docs (DTYPE_MATRIX / HARDWARE / KV_MATH / QUANTIZATION): corrected the
"Blackwell sm >= 10.0" framing to "datacenter sm_100/103 only".
- UPSTREAM.md: #43562 / TRT-LLM #10241 row + re-test trigger.
- test-arch-ab: nvfp4 refuses on sm_86 AND sm_120, allowed on sm_100;
the dual-5090 all-arms test drops nvfp4.
Full scripts gate 66/66.
Co-Authored-By: Claude Fable 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01EfF565T9eSLaqGzidyJ1Pm
