User-Space GPU Direct Storage Development Kit

uGDS is the first production-oriented user-space GPU Direct Storage library where the CPU constructs NVMe commands and the SSD DMAs data directly to/from GPU memory over PCIe, bypassing the kernel NVMe driver. With a GDS-compatible API, uGDS achieves up to 5.3x higher bandwidth and 108x lower 4KB latency (5.2μs vs 561μs) compared to NVIDIA GDS.

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Key Features

• User-space IO stack — bypasses the kernel NVMe driver and filesystem entirely; CPU builds NVMe commands and polls completions in user space
• cuFile API compatible — existing GDS applications work with minimal changes (relink to libugds.so, change cuFile prefix to uGDS)
• Multi-vendor GPU support — NVIDIA CUDA and AMD Infinity Storage (HIP/ROCm) backends; both can be enabled simultaneously for mixed-GPU systems
• Fully open-source — BSD 3-Clause licensed; no proprietary runtime dependencies beyond the GPU driver (NVIDIA driver or AMD ROCm runtime)
• High performance — busy-poll CQ completion with _mm_pause(), multi-queue round-robin IO, achieving up to 2.7x read and 28x write bandwidth over NVIDIA GDS

Architecture

┌──────────────┐
│  Application │    uGDSRead / uGDSWrite
└──────┬───────┘
       │
┌──────▼───────┐
│  libugds.so  │    NVMe command construction + SQ/CQ management
└──────┬───────┘
       │          DMA: SSD ←→ GPU memory (P2P over PCIe)
┌──────▼───────┐
│  ugds_drv.ko │    PCI BAR mapping + GPU page pinning
└──────┬───────┘
       │
┌──────▼───────┐
│   NVMe SSD   │
└──────────────┘

No kernel NVMe driver, no page cache — the CPU only touches doorbell registers and completion queue entries.

Performance

16-thread sequential read bandwidth on A100-40GB + Samsung 990 PRO (PCIe Gen4 x4):

uGDS bypasses the kernel NVMe driver, achieving up to 2.7x higher read bandwidth and 28x higher write bandwidth than NVIDIA GDS at small IO sizes.

Quick Start

#include <ugds.h>
#include <cuda_runtime.h>

// 1. Initialize
uGDSDriverOpen();

// 2. Register device handle
int fd = open("/dev/ugds_drv0", O_RDWR);
uGDSDescr_t desc = {.type = UGDS_HANDLE_TYPE_OPAQUE_FD, .handle.fd = fd};
uGDSHandle_t fh;
uGDSHandleRegister(&fh, &desc);

// 3. Allocate and register GPU buffer
void* gpu_buf;
cudaMalloc(&gpu_buf, 4096);
uGDSBufRegister(gpu_buf, 4096, 0);

// 4. Direct GPU ←→ SSD transfer
uGDSWrite(fh, gpu_buf, 4096, /*file_offset=*/0, /*buf_offset=*/0);
uGDSRead(fh, gpu_buf, 4096, /*file_offset=*/0, /*buf_offset=*/0);

// 5. Cleanup
uGDSBufDeregister(gpu_buf);
uGDSHandleDeregister(fh);
uGDSDriverClose();

See examples/01_basic_read_write.cu for a complete working example.

For build instructions, environment setup, and driver management, see the Installation Guide.

AMD Infinity Storage (HIP/ROCm) Backend

To build with the AMD HIP backend instead of CUDA:

# Kernel module (HIP-only if NVIDIA source is present, add BUILD_CUDA=0)
cd drv && make BUILD_HIP=1 BUILD_CUDA=0

# Userspace library
mkdir build && cd build
cmake .. -DUGDS_BACKEND_HIP=ON -DUGDS_BACKEND_CUDA=OFF
make -j$(nproc)

Requires ROCm 5.6+, CONFIG_HSA_AMD_P2P=y, and Large BAR enabled. See the Installation Guide for details.

Testing

# Run functional tests only
scripts/run_tests.sh functional

# Run uGDS performance benchmark
scripts/run_tests.sh perf

# Run uGDS vs GDS comparison (auto-switches driver mode)
scripts/run_tests.sh compare

# Run all (functional + comparison)
scripts/run_tests.sh all

API Coverage

API	Status	Notes
uGDSDriverOpen / Close	✅
uGDSHandleRegister / Deregister	✅	Block device fd (no filesystem)
uGDSBufRegister / Deregister	✅	GPU memory only
uGDSRead / Write	✅	Synchronous, block-aligned
uGDSBatchIOSetUp / Submit / GetStatus / Destroy	✅	Submit/poll separation, up to 128 IOs per batch
uGDSReadAsync / WriteAsync	✅	CUDA stream integration, late-binding pointers
uGDSStreamRegister / Deregister	✅	Optional (no-op, uGDS has no bounce buffer)

Roadmap

Phase	Description	Status
1	Core synchronous API + test suite	✅
1.5	Unified multi-backend (NVIDIA CUDA + AMD HIP/ROCm)	✅
2	Batch IO API (multi-command doorbell)	✅
3	Async Stream API (CUDA stream integration)	✅
4	Hugepage support (larger QP depth)	✅
5	SGL support (scatter-gather lists)	🔜
6	Interrupt mode (MSI-X + eventfd)	🔜
7	Multi-SSD support (multi-handle aggregation)	🔜
8	Striping (automatic IO distribution across SSDs)	🔜
9	Filesystem compatibility (POSIX file path support)	🔜
10	LMCache integration (KV cache storage backend)	🔧

Citation

uGDS originated from the motivation experiments in CoPilotIO. If you find uGDS useful in your research, please cite:

@inproceedings{chen2026copilotio,
  title     = {CoPilotIO: CPU as a Co-pilot for GPU I/O to Free GPU Compute},
  author    = {Guanyi Chen and Qi Chen and Shu Yin and Jian Zhang},
  booktitle = {Proceedings of the 20th USENIX Symposium on Operating Systems Design and Implementation (OSDI '26)},
  year      = {2026}
}

References

• ssd-gpu-dma — User-space NVMe driver with GPU support
• BaM — Big accelerator Memory, GPU-orchestrated NVMe access
• Phoenix — GPU Direct Storage Optimization

Contact

• Guanyi Chen — felixlinker02@gmail.com — chengy-sysu.github.io
• Jian Zhang — jianz@hkust-gz.edu.cn — sosp.dev

License

BSD 3-Clause License. See LICENSE.