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OdinLink-Five

Thunderbolt 5 RDMA for Linux — kernel driver, libibverbs provider, NCCL/RCCL plugins

OdinLink turns a Thunderbolt cable into a high-speed RDMA interconnect between machines. It provides the full ibv_* verbs API so any verbs-aware application (NCCL, MPI, PyTorch DDP) can use Thunderbolt DMA without code changes.

80 Gbps  ·  sub-µs latency  ·  zero-copy GPU  ·  standard ibv_verbs API

#Thunderbolt 4 Test / USB4v1

USB4v1 / Thunderbolt 4 Test

#Thunderbolt 5 Test / USB4v2 USB4v2 / Thunderbolt 5 Test

Progress

Layer Component Status
🟢 Kernel module (odl_tb5.ko) NHI ring DMA, XDomain handshake, loopback mode
🟢 Userspace library (libodl_tb5.so) C API, stream I/O, mmap, DMA-buf
🟢 Verbs provider (libodl_tb5_verbs.so) ibv_open_device, ibv_reg_dmabuf_mr, QP/CQ lifecycle
🟢 rdma-core plugin (libodl_tb5-rdmav34.so) Auto-discovered by ibv_devinfo
🟢 Async I/O poll() + O_NONBLOCK ioctls end-to-end
🟢 No-cable testing loopback=1 module param + mock library
🟢 RCCL/NCCL net plugin Supported GPU path — librccl-net.so / libnccl-net-ODL_TB5.so (see docs/GPU.md)
🟡 NCCL verbs / IB transport Works only with LD_PRELOAD=libodl_tb5_verbs.so health checks; RCCL dlopens libibverbs and bypasses preload — use the net plugin
🟡 rdma-core provider plugin Needs a sysfs RDMA device to load; inert on OdinLink-only hosts — use LD_PRELOAD for ibv_devinfo
🟡 Async DMA-buf Needs callback-based cleanup — stream path is already async via poll()

Quick Start

Build & Run

sudo apt install build-essential cmake linux-headers-$(uname -r) libibverbs-dev rdma-core pkg-config gcc-14
git clone https://github.com/johndpope/OdinLink-Five.git
cd OdinLink-Five && mkdir build && cd build
cmake .. -DBUILD_VERBS=ON && make -j$(nproc) odl_tb5_verbs odl_tb5_verbs_provider

# Test without cable:
sudo insmod driver/odl_tb5.ko loopback=1
ibv_devinfo                     # Should show odl_tb5 device
build/verbs/tests/test_verbs_basic

Point-to-Point (two machines)

# Machine A:
sudo insmod driver/odl_tb5.ko
build/cli/odl_tb5_cli server -d 0

# Machine B (wait for dmesg "entering READY state" first):
sudo insmod driver/odl_tb5.ko
build/cli/odl_tb5_cli client -d 0 -t bandwidth -b 64K,1M,4M

RCCL (AMD) — use the net plugin, not verbs/IB

cmake --build . --target rccl_net_odl_tb5
# Build tree already has librccl-net.so symlink; or:
export LD_LIBRARY_PATH=$PWD/rccl:$PWD/lib:$LD_LIBRARY_PATH
# Confirm logs say:  Using network ODL_TB5   (NOT Socket)

Full install guide → docs/INSTALL.md · GPU → docs/GPU.md

Architecture

┌────────────────────────────────────────────────────┐
│  Application (NCCL, MPI, PyTorch, ibv_* API)       │
├────────────────────────────────────────────────────┤
│             libibverbs (libibverbs.so.1)            │
├────────────────────────────────────────────────────┤
│  libodl_tb5-rdmav34.so  (verbs provider plugin)    │
├────────────────────────────────────────────────────┤
│  libodl_tb5.so  (OdinLink C API)                   │
├────────────────────────────────────────────────────┤
│  odl_tb5.ko  (kernel module — NHI DMA)             │
├────────────────────────────────────────────────────┤
│  Thunderbolt 5 NHI DMA Engine                       │
└────────────────────────────────────────────────────┘

Components

Component Binary Description
Kernel driver odl_tb5.ko NHI ring DMA, XDomain handshake, char device
Library libodl_tb5.so C API wrapping ioctls, streams, mmap
Verbs provider libodl_tb5_verbs.so Standalone ibv_* via symbol interposition
Verbs plugin libodl_tb5-rdmav34.so rdma-core provider plugin (ibv_devinfo)
NCCL plugin libnccl-net-ODL_TB5.so NVIDIA GPU collectives
RCCL plugin librccl_net_odl_tb5.so AMD GPU collectives
CLI tool odl_tb5_cli Bandwidth, latency, jitter, MIMO tests
Loopback module loopback=1 param Fake peer for no-cable testing
Mock library libodl_tb5_mock.so LD_PRELOAD simulation (no kernel needed)

GPU and daemon/tray → docs/GPU.md, docs/INSTALL.md

Verbs API Coverage

Operation Status Notes
ibv_open_device ✅ Symbol interposition + rdma-core plugin
ibv_query_device ✅ Attributes from peer info
ibv_query_port ✅ Port state from peer connection
ibv_alloc_pd / ibv_dealloc_pd ✅ Protection domains
ibv_reg_mr / ibv_dereg_mr ✅ Host memory registration
ibv_reg_dmabuf_mr ✅ Zero-copy GPU memory (Linux DMA-buf)
ibv_create_cq / ibv_destroy_cq ✅ Eventfd-based completion queues
ibv_poll_cq / ibv_req_notify_cq ✅ Poll + eventfd notification
ibv_create_qp / ibv_destroy_qp ✅ RC QP → stream mapping
ibv_modify_qp ✅ RESET → INIT → RTR → RTS
ibv_post_send ✅ Async via workqueue + poll()
ibv_post_recv ✅ Non-blocking via poll()
ibv_query_qp ✅ State + capabilities

Async I/O Model

ibv_post_send(qp, wr, NULL)
    │
    ▼  (non-blocking, returns immediately)
Enqueue WR → per-QP submission queue
    │
    ▼  (worker thread)
poll(fd, POLLOUT)  ← kernel signals TX readiness
    │
    ▼
ioctl(STREAM_SEND) ← O_NONBLOCK, never blocks
    │
    ├── -EAGAIN → re-queue WR, poll again
    └── success → post struct ibv_wc → CQ → eventfd

Testing Without Hardware

# Option 1: kernel loopback (real module, fake peer)
sudo insmod driver/odl_tb5.ko loopback=1
build/verbs/tests/test_verbs_basic

# Option 2: user-space mock (no kernel module at all)
mkfifo /dev/odl_tb5_0
LD_PRELOAD=verbs/tests/libodl_tb5_mock.so \
  LD_LIBRARY_PATH=build/verbs:build/lib \
  build/verbs/tests/test_verbs_mock_loopback

Smoke Tests (with hardware)

Verbose logging is essential for diagnosing failures. Use the provided helper script which captures everything automatically:

# Full smoke test suite — all logs go to smoke-test-<timestamp>/:
./scripts/smoke-test.sh

# Run only the verbs provider test:
./scripts/smoke-test.sh -t verbs

# Bandwidth test (two machines, machine A first):
sudo ./scripts/smoke-test.sh -t bandwidth -m server   # Machine A
sudo ./scripts/smoke-test.sh -t bandwidth -m client   # Machine B

# Custom output directory:
./scripts/smoke-test.sh -o /tmp/odl-debug

Verbose logging is also available manually:

# Watch kernel driver logs (run in a separate terminal):
sudo dmesg -w | grep odl_tb5

# Trace all verbs calls — set level 1–5 (5 = most verbose):
export ODL_VERBS_DEBUG=5

Manual smoke test steps

1. Kernel module + device node

sudo insmod driver/odl_tb5.ko
sudo chmod 666 /dev/odl_tb5_0    # allow non-root access
ls -l /dev/odl_tb5_0             # appears only when a TB5 peer is connected

2. Full test suite (3 suites: device, lib API, plugin)

build/tests/odl_tb5_test

3. Verbs provider lifecycle test

build/verbs/tests/test_verbs_basic

Exercises: device discovery, context open, PD/MR/CQ/QP lifecycle, post_send/post_recv.

4. End-to-end bandwidth (two machines)

# Machine A:
build/cli/odl_tb5_cli server -d 0

# Machine B (wait for dmesg: "odl_tb5: entering READY state"):
build/cli/odl_tb5_cli client -d 0 -t bandwidth

5. ibv_devinfo discovery

# Preferred health check on OdinLink-only hosts (no other RDMA NIC):
LD_PRELOAD=build/verbs/libodl_tb5_verbs.so ibv_devinfo

# The rdma-core directory plugin (libodl_tb5-rdmav34.so) only loads when
# sysfs already exposes an unclaimed RDMA device — on pure OdinLink machines
# it is inert. See docs/TROUBLESHOOTING.md.

Module Parameters

Param Default What it does
e2e=0 1 (on) Disables end-to-end flow control handshake. Only needed for old TB3 controllers that choke on E2E. TB4/TB5 leave this alone.
loopback=1 0 (off) Creates fake devices with no cable — data loops back inside your own machine. For testing without a peer.
protocol=1 0 (OdinLink) Switches to Apple's protocol ID (0xFA57) so macOS peers can discover OdinLink. For Mac↔Linux only.
odl_ring_size=1024 4096 Number of DMA packet slots per ring. Larger = smoother bursts, more RAM. On iommu=pt (identity IOMMU) hosts the default may fail to allocate — use 1024, or let probe auto-downgrade. 
# Examples:
sudo insmod driver/odl_tb5.ko                       # TB4/TB5, default everything
sudo insmod driver/odl_tb5.ko e2e=0                 # old TB3 controller
sudo insmod driver/odl_tb5.ko loopback=1            # no cable, just testing
sudo insmod driver/odl_tb5.ko protocol=1            # talk to macOS
sudo insmod driver/odl_tb5.ko odl_ring_size=1024    # iommu=pt / RAM-constrained

Debug

export ODL_VERBS_DEBUG=5     # Trace all verbs calls
sudo dmesg -w | grep odl_tb5 # Kernel driver logs

Troubleshooting → docs/TROUBLESHOOTING.md

Cross-Platform: macOS

Apple ships libthunderboltrdma.dylib + libibverbs on macOS 26.5, but the kernel extension is a stub — IORDMAFamily is not shipped. Mac Thunderbolt RDMA is not currently functional. OdinLink is the only working implementation. See COMPAT.md.

Repository

Resource Link
Install guide docs/INSTALL.md
GPU / NCCL / RCCL docs/GPU.md
Troubleshooting docs/TROUBLESHOOTING.md
Packaging / .deb docs/PACKAGING.md
Agent instructions AGENTS.md
Verbs provider manual verbs/VERBS_PROVIDER.md
Cross-platform compat COMPAT.md

License

  • Kernel driver (odl_tb5.ko): GPL v2
  • All userspace: MIT

About

A high-performance RCCL / NCCL (ROCm Communication Collectives Library) plugin for Thunderbolt 5 that enables GPU-to-GPU communication across Thunderbolt connections with RDMA support.

Topics

aiamdappledriverhigh-performance-computinghiplinux-kernelnvidiarocmthunderbolt

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