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Windows ARM64 and NVIDIA RTX Spark N1X (sm_121) native CUDA support - #1010

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Summary

Rebases the native Windows CUDA port (#836, preserving @BobClawblaw's 29 commits) onto current main (1.0.12, 6ee828c2) and completes native aarch64-windows + NVIDIA RTX Spark N1X (sm_121) support (60ba6961):

  1. Windows Unified-Memory CUDA Admission (zig/src/native/cuda.zig, zig/src/native/cuda_memory.zig):
    • On NVIDIA RTX Spark N1X (sm_121), cuDeviceGetAttribute(.integrated) returns 1 (unified = true).
    • Previously, pool() unconditionally read /proc/meminfo whenever unified was true, causing every model load on Windows integrated/unified-memory GPUs to fail closed with cannot read or parse /proc/meminfo's MemTotal and MemAvailable; refusing CUDA unified-memory admission.
    • On Windows WDDM, cuMemGetInfo_v2 (ctx.memInfo()) already reports the combined WDDM device pool (dedicated carveout + shared system memory budget) and tracks cuMemAlloc reductions directly.
    • pool() now reads /proc/meminfo only on !platform.windows while keeping unified = true on Windows so the 10% unified-memory reserve floor (at_least = 4 GiB, least = 2 GiB) and ", memory shared with the host" startup notice remain active.
  2. RTX Spark Hardware Detection & NPU Filtering (zig/src/server/benchmark_host.zig, zig/src/server/benchmark_facts_test.zig):
    • On RTX Spark N1X, nvidia-smi --query-gpu=name,memory.total,driver_version --format=csv,noheader,nounits outputs a second row for the integrated NPU (NVIDIA NPU, [N/A], 617.42), which caused nvidiaRows to include a memoryless entry and downgrade hardware detection to "partial".
    • modelName() now filters "NVIDIA NPU", and summarize() classifies "NVIDIA RTX Spark" alongside "NVIDIA GB10" as "unified" memory.
  3. aarch64-windows Relative DLL Loading in Host Tests (zig/src/platform/sys.zig, zig/tests/hip_mock.c):
    • LoadLibraryW fails with ERROR_MOD_NOT_FOUND (126) when given relative paths containing path separators (such as .zig-cache\o\...\hip-mock-success.dll). WinDynLib.open now normalizes / to \ and resolves paths containing path separators via GetFullPathNameW before calling LoadLibraryW, and hip_mock.c marks mock symbols __declspec(dllexport) on _WIN32.
  4. Documentation (docs/WINDOWS.md):
    • Documents aarch64-windows (vcvarsall.bat arm64_amd64) and -Dsm=121 build/test support and Windows unified-memory admission behavior.

Verification Receipts (aarch64-windows, NVIDIA RTX Spark N1X sm_121, CUDA 13.4)

  • Host & Golden Suites:
    • zig build test test-kernel-contract test-golden fuzz-cortheon --summary all
    • 96/96 build steps succeeded; all host unit tests pass (0 failures, including hip-host-test dynamic library tests and benchmark_facts_test.zig RTX Spark / NPU tests)
    • test-golden: 306/315 equal to frozen Python answers, 0 unexpected differences
    • fuzz-cortheon: 7/7 pass
  • Native sm_121 Build & GPU Suites (tf-cuda-test.exe):
    • Built tensorfold-native.exe and tf-cuda-test.exe natively on aarch64-windows with -Dsm=121 (Zig 0.17.0 + MSVC + CUDA 13.4 V13.4.92)
    • Passed all 15 GPU suites on NVIDIA RTX Spark N1X (48 SMs, sm_121): info, smoke, graph, launch-ex, ptx, symbols, cublaslt, norms, norm-rows, sample, glue (1,293/1,293 byte-equal), pocket, quant-ref, modelopt, exlr8, and exlr8-dense
    • Passed all 12 kernel-contract numerical, repeatability, shape, and sum gates + all 5 planted controls on sm_121
    • Verified tensorfold-native.exe serve admits through pool() on RTX Spark N1X and enforces the 2 GiB minimum / 10% default unified-memory reserve floor
  • Hygiene:
    • zig fmt --check build.zig zig and git diff --check: clean
    • python tools/zig/lean_check.py: 0 new findings

BobClawblaw and others added 30 commits October 17, 2026 12:54
- zig/src/platform: `sys`, imported by every module (zig/build/sys.zig wires
  it). On POSIX it is std.c, std.posix and std.DynLib unchanged; on Windows
  win_c.zig gives libc's surface over the UCRT and Win32 (integer
  descriptors, directory descriptors, readdir, pread/pwrite, high-resolution
  sleep, monotonic clock, /tmp and /proc/self/exe mapped), win_posix.zig the
  server's sockets over Winsock, console events as SIGINT/SIGTERM, and
  LoadLibraryW for DynLib.
- std.c and std.DynLib calls go through `platform` (mechanical).
- build.zig routes Windows targets to the CUDA build.
- Server: socket closes and writes are explicit, the key file's mode check
  is skipped on NTFS (ACLs), descriptor limits are a no-op.
- shard_edit: the shard's map is released before the rename, since Windows
  refuses to replace a mapped file.
- Tests that need symlink privilege or mode bits skip on Windows.

zig build test-cuda-host passes on x86_64-windows.
- Kernel fatbins build with nvcc and cl.exe: MSVC's conforming
  preprocessor is passed on Windows hosts (CUDA 13's headers need it),
  and explicit kernel instantiations carry the __restrict__ qualifiers
  their templates have (MSVC counts them in the function type; the
  generated code is unchanged).
- Nemotron's checkpoint source keeps io_uring to Linux; elsewhere its
  existing thread reads run.
- pull_exlr8 raises no descriptor limit on Windows.
- modelopt test: the lane's slice partials are allocated. GPUs without
  clusters (before sm_90) reduce split K through them; the test passed
  none, so it wrote through a null pointer on Ampere and Ada.

zig build native and install build with -Dnvcc=... -Dsm=89, and
tf-cuda-test's synthetic suites pass on an RTX 4090.
- pull: where Windows refuses the snapshot's symlink, the snapshot path
  becomes a hard link to its blob (CreateHardLinkW through `sys.c.link`):
  no extra space, and learning already refuses linked shards. Link
  failures are logged with their reason.
- HOME falls back to USERPROFILE (Windows sets no HOME) for the hub cache
  and every libc getenv("HOME").
- Tests read optional fixture variables through `platform.getenv`;
  std.process.Environ.getPosix does not build on Windows.
- The learned-state symlink tests skip on Windows (symlinks need
  privilege); `sys.c.symlink` asks for an unprivileged one.

zig build test passes on x86_64-windows.
- docs/WINDOWS.md: requirements, build, run, how the port works and how it
  differs from Linux; the README points to it.
- -Dstrip reaches tensorfold-native before its install step is made, so
  the step no longer expects a .pdb the stripped build does not write.
- zig fmt on the platform files.
8080 and 8000 are taken by too many other servers; serve listens on 8888
unless --port says otherwise, and the docs and bench scripts follow.
The MLX affine 4-bit checkpoint on the native CUDA server, beside Nemotron:
qwen35.cu holds the Metal engine's glue at its bf16 rounding points (gated
delta rule, causal convolution, gated attention), cuda.qlinear's affine-4
kernels do the projections, sample.cu draws on the device.

Windows of up to 16 rows record each row's recurrence and convolution tail,
so the lane core shares rounds across streams and keeps partial copies; a
window's rows equal one-row steps bit for bit. draw.zig is the host draw
both backends now share.

On an RTX 4090: 210 tok/s for one stream, 1250 tok/s across eight; logits
agree with an fp32 reference at every position of a 36-token check.
…mory

The 2B's CUDA engine now reads its widths from config.json (cuda_geometry.zig):
linear value heads over fewer key heads, more query heads a key/value head,
an untied head, an A_log stored as bf16. The 27B's logits agree with an fp32
reference at every position of a 36-token check, and its windows equal
one-row steps bit for bit; the 2B's output is unchanged.

Two Windows driver costs shaped the rest. Each kernel launch grew with the
process's allocation count (1.2 ms a launch over 1,900 weight buffers), so a
model's weights and scratch now live in one arena (cuda_weights.zig packs
each projection through a reused staging buffer: the 27B loads in 25 s, not
200). And a process's first forwards through a buffer stall for seconds, so
the engine warms every request path at load and the backend keeps a pool of
stream caches that `reserve` allocates and runs a row through once the
server knows its stream count.

On an RTX 4090: the 27B decodes at 37 tok/s in the runner, 31 to 35 tok/s
served, 210 tok/s across eight streams; the 2B stays at 210 and 1,250.
A forward's launches (the embedding to the kept rows' logits) are captured
the first time a shape (rows, windows, recording) is seen and replayed after;
the attention chunk count moves into the per-forward table so a graph stays
valid as caches grow. Prompt chunks stay uncaptured: their GEMMs dwarf the
launches, and each length would be a graph of its own.

A new graph's first run pays the Windows driver's stall (about a second on a
wide model), so `reserve` also captures the shared rounds' shapes, a row of
each of 1 to n streams, at load.

Bit for bit the same logits; on an RTX 4090 the 2B steps in 2.8 ms instead of
5.3 (served: 324 tok/s, 1,560 across eight streams) and the 27B in 23.8 ms
instead of 26.9 (served: 40 tok/s, 243 across eight).
--drafter loads z-lab's DFlash2 draft model behind the lane core's Drafted
wrapper: the target writes each row's residual after the drafter's five
tapped layers into a ring a stream, the drafter folds those rows into a
context of keys and values, and after every verify it drafts a block of
seven tokens past the pending one (the target's own embedding and head at
its ends, a codebook selector tracing one path through each row's best
sixteen). Its projections are quantized to affine-4 on the host at load and
run through the target's kernels; its glue is qwen35_draft.cu.

The Windows driver stalls a buffer's first kernel and a new graph's first
run for seconds, so the drafter pools its contexts and a captured forward
now serves every verify shape: its launches cover a bucket of rows and
every window, and the kernels read the true counts from the device.

On an RTX 4090 the 27B serves 52 to 58 tok/s greedy with drafts against 40
plain, about 100 tok/s on long replies, the same tokens either way; plain
decoding keeps its 24 ms step. The 2B is unchanged.
A verify window's rows may form a tree (each row's parent given): the
convolution taps, the delta rule and attention follow each row's own
branch, and the DFlash2 drafter fills the lane core's planned lanes
(each lane its parent's rank-r choice by the codebook selector), so a
lone stream verifies up to 12 lanes a round and the planner learns
which shapes land.

A verify no longer snapshots every row's state (1.3 GB shared, which
capped the 27B at 8 rows): each stream logs its rows' decay, write and
key, and keep replays the kept path onto the recurrence in one pass
(and moves a tree's kept keys down), so any window width fits. One-row
steps and prompts update in place as before. The lane host times the
target's windows at load, which the depth rule had lacked (it had been
capping chains at 3 drafts).

The runner's new tree mode verifies tree windows with junk branches
against step logits (bit-exact on both models).
What the port serves beyond Nemotron: Qwen3.5-2B and Qwen3.8-27B with
its DFlash2 drafter, the speeds measured on an RTX 4090, the load time
and why, the timing and chain-only switches, and what is not there.
The lean rule (tools/zig/lean_check.py) counts a comment that runs on
to a second line; the Windows port's new files had a hundred such runs.
Each is one line of at most 120 columns now, and the checker reports
the same 539 problems as main.
direct_io opened files with O_DIRECT on Linux alone. On Windows the
same open now asks for FILE_FLAG_NO_BUFFERING (which win_c maps O_DIRECT
to), and the 4 KiB-aligned spans it already reads satisfy the sector
alignment that needs; a file system that refuses it still falls back to
buffered reads. The direct-read test runs on Windows too, checking the
executable's bytes against buffered reads of it.
SIG.IGN is a function pointer made from 1, as std.posix has it. aarch64
requires function pointers to be aligned unless the type says align(1),
so the cross-build for aarch64-windows refused it. With align(1), as
std's own handler type has, tensorfold-native cross-compiles for
aarch64-windows with the GB10 (sm_121) fatbins; no hardware has run it.
The Windows page opens with what the build is, what it is tested on and
that it cross-compiles for aarch64-windows; the README's model table
and the CUDA paragraph say Windows where they said unofficial port.
The no-GPU workflow runs zig build test on windows-latest beside
ubuntu-latest, so the platform layer is built and tested on every pull
request.
Every other module calls libc through `sys`; the drafter's four getenv
calls were the last direct std.c calls in a file the Windows build
compiles.
After a prompt the lane core hands the drafter every prompt row's
features; the CUDA backend refused any request wider than its tap ring
(2,176 rows), so a 27B request with --drafter and a prompt past that
ended with RowsNotHeld, where the same prompt without the drafter ran.
The ring keeps the newest tap_rows rows, which hold the drafter's whole
context window, and absorb already reads only that window of what it is
handed; the backend now refuses only rows not yet written or all gone.

On an RTX 4090 the 27B with its drafter takes a 6,041-token prompt in
7.4 s, and its reply equals the one with "draft": false.
… attention cuts chunks at logical positions

- rowanc held a window's rows as bits of a u32, but prompt chunks run up to
  128 rows: rows from 32 on rotated at the wrong positions and attended the
  wrong keys. A chain row (no parents) now carries its index in its window
  under the top bit; tree windows (at most 16 rows) keep their bits.
- tf_q35_attn_partial cut its 128-key chunks at a key's cache row, so a kept
  tree path whose window crossed a chunk boundary summed in other chunks than
  one-row steps and changed bits. Chunks are now cut at the key's logical
  position (the stream's length plus the ancestors before it).

Checked on an RTX 5090 (Linux, sm_120), tf-qwen35-cuda over 300 ids on
Qwen3.5-2B and Qwen3.8-27B: step bits unchanged, window and tree equal step
byte for byte (tree differed from row 126 on the 2B and 254 on the 27B
before). Prompt mode's last row against step's at 16 to 300 ids: KL at most
0.003 and the same argmax in 20 of 20 (before: 27B at 40 ids KL 2.3 with a
different argmax, at 128 ids KL 1.35).
zig build test-golden and zig build fuzz-cortheon exist on every non-macOS
host since the golden step moved into zig/build/golden.zig, so the golden
check compiles against the platform layer on Windows:

- the platform's posix gains sockaddr.in, timeval, connect and kill for a
  child's handle (TerminateProcess; HUP has no equivalent), setsockopt turns
  a timeval for SO_RCVTIMEO or SO_SNDTIMEO into Winsock's milliseconds, and a
  socket read that times out is WouldBlock, as std.posix reports it.
- the check carries SystemRoot into the spawned server's environment, which
  Winsock needs to start, and drains the server's stdout after the port line
  on every host: the fake server logs each request there, and a full pipe
  (4 KiB on Windows) blocked it after sixteen cases.
- on Windows the check cannot send SIGTERM or SIGHUP, so the sigterm-exit-0
  outcome and the cases after a key rewrite are skipped and printed as such.

On Windows the goldens give 306 of 315 equal with the same nine known
differences as Linux, and the fuzz step passes its eight tests; the no-GPU
workflow's Windows job runs both.
The loader tried only libcublasLt.so.13 and libcublasLt.so, so the
cublaslt suite of tf-cuda-test reported LibraryUnavailable on Windows;
there it opens cublasLt64_13.dll from the toolkit's bin folder.
The platform handed O_APPEND to the C runtime as _O_APPEND, whose write
seeks to the end and then writes, so two threads appending at once could
overwrite each other's bytes: the request log lost lines under concurrent
requests, which the server goldens' request-log case caught on a slow
runner. A descriptor opened with O_APPEND now writes through WriteFile at
the end-of-file offset, which the kernel places whole, as POSIX does; the
file keeps its write access, so ftruncate on such a descriptor still works
(prompt_imprint repairs a torn index that way).

A request_log test appends 200 lines from each of 8 threads and expects
every line whole; it lost lines on Windows before this change.
The lifecycle/request-log outcome said only that the lines differ; it now
gives both logs' line counts and the first line that differs, cut to 100
bytes each, so a mismatch seen on a CI runner can be read from its log.
A checkout with core.autocrlf, as GitHub's Windows runners make, gives the
frozen request log CRLF line endings while the server writes LF, so the
lifecycle/request-log case differed at its first line's end on windows-latest
and nowhere else. Both logs compare with CRLF read as LF; the other goldens
are parsed as JSON and never saw the endings.
…'s widest stream

The chunk width came from the longest stream or window in the forward, so a 201-key row cut its keys into 128-key
chunks alone and 256-key chunks beside a stream past 8192, and a window crossing 8192 recut its earlier rows; either
changed the fp32 sums. Each row now takes chunk_keys(its logical keys), the width its one-row step uses, in both the
partial and the merge kernels, and the partials sit at a fixed max_chunks stride.

tf-qwen35-cuda takes TF_Q35_PREFILL=N (start after N cycled ids) and TF_Q35_BESIDE=N (step an N-token stream in each
forward), which cover both cases: before this change, windows from 8151 keys kept 36 of 120 rows and trees 35, and a
151-key stream beside one from 8189 kept 4 to 11 of 120; after it all of them equal one-row steps on the 2B and 27B.
…fits its selector rank

The integer reader accepted zero, so a conv_group_size or num_key_value_heads of 0 reached a remainder at
admission; sizes and divisors are now positive (mask_token_id alone may be 0). The host staging area held 16 rows at
rank 256, so a larger selector_rank overran it; it is now sized for the admitted rank. Config.parse takes the bytes,
so a host test covers both.
The release's new modules called libc and POSIX directly, so zig build test and zig build native stopped building on Windows. They now go through sys, as the rest of the tree does:

- std.c and std.posix calls become sys.c and sys.posix: recall's store, the rows store and its files, originals, the hip engine's timers and comm links, the XPU loader, tp_watch, the lanes' recorder, and their tests. The clock calls take CLOCK.MONOTONIC, a value Windows' clock_gettime accepts.
- win_c gains flock (win_lock.zig: LockFileEx over a file's first byte, or over `.tensorfold-lock` inside a directory descriptor, AGAIN when held against) and _exit. win_posix gains IPPROTO, TCP.NODELAY and the keepalive options, SO.KEEPALIVE, SOCK.CLOEXEC (0), system.read and system.poll, and sockaddr.in's default family.
- libjpeg-turbo, libtfvideo and RCCL load through sys.DynLib (turbojpeg.dll, tfvideo.dll on Windows); sys.libraryOf names a symbol's library where dladdr does elsewhere.
- eaq_container's "inside the pack's folder" check takes either separator, so a Windows path's shards are not refused as outside.
- The fake fabric's windows come from the page allocator rather than mmap.
- nvcc gets -D_USE_MATH_DEFINES on Windows hosts, for vit.cu's M_SQRT2.
- Refused by name on Windows: `tensorfold benchmark` (its serve child runs under POSIX signals and waits; its tests build elsewhere) and image URLs in media_fetch.
- Tests that make symlinks skip without the privilege, and the owner-only mode checks skip, as Windows files have none.

--drafter's Served also reserves the family's own streams, so native/cuda.zig stays within 600 lines.
…e on Windows, where an exclusive create follows a dangling one
- Admit unified-memory CUDA GPUs on Windows via WDDM/cuMemGetInfo_v2 without requiring Linux /proc/meminfo, while keeping the 10% unified-memory reserve floor and shared-memory startup notice.
- Filter the non-GPU 'NVIDIA NPU' row from nvidia-smi and classify 'NVIDIA RTX Spark' alongside 'NVIDIA GB10' as unified memory in benchmark_host.zig.
- Resolve relative DLL paths via GetFullPathNameW in WinDynLib.open and export mock HIP symbols on _WIN32 so zig build test passes on aarch64-windows.
- Document aarch64-windows / sm_121 RTX Spark N1X build and unified-memory behavior in docs/WINDOWS.md.
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