DMA Copy

DMA Copy (PDF)

NVIDIA DOCA DMA Copy Application Guide

This guide provides an example of a DMA Copy implementation on top of NVIDIA® BlueField® DPU.

DOCA DMA (direct memory access) Copy application transfers files (data path) up to 1MB in size between the DPU and the x86 host using the DOCA DMA library which provides an API to copy data between DOCA buffers using hardware acceleration, supporting both local and remote memory.

DOCA DMA allows complex memory copy operations to be easily executed in an optimized, hardware-accelerated manner.

DOCA DMA Copy is designed to run on both the instances of the BlueField-2 DPU and x86 host. The DPU application must be the first to spawn as it opens the Comm Channel (CC) service between the two sides on which all the necessary DMA library configuration files (control path) are transferred.

system-design-diagram.png

DOCA DMA Copy runs on top of DOCA DMA to read/write directly from the host's memory without any user/kernel space context switches, allowing for a fast memory copy.

application-architecture-diagram.png

  1. The two sides initiate a short negotiation in which the file size and location are determined.
  2. Host side creates the export descriptor with doca_mmap_export() and sends it with the local buffer address and length on the Comm Channel to the DPU side application.
  3. DPU side application uses the received export descriptor to create a remote memory map locally with doca_mmap_create_from_export() and the host buffer information to create a remote DOCA buffer. From this point on, the DPU side application has all the needed memory information and the DMA copy will take place.

This application leverages following DOCA libraries:

  1. Parse application argument.
    1. Initialize arg parser resources and register DOCA general parameters.
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      doca_argp_init();

    2. Register application parameters.
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      register_dma_copy_params();

    3. Parse app flags.
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      doca_argp_start();

  2. Initialize DOCA App Shield lib context.
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    init_cc();

    1. Create Comm Channel endpoint.
    2. Parse user PCIe address for Comm Channel device.
    3. Open Comm Channel DOCA device.
    4. Parse user PCIe address for Comm Channel device representor (on DPU side).
    5. Open Comm Channel DOCA device representor (on DPU side).
    6. Set Comm Channel endpoint properties.
  3. Open the DOCA hardware device from which the copy would be made.
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    open_dma_device();

    1. Parse the PCIe address provided by the user.
    2. Create a list of all available DOCA devices.
    3. Find the appropriate DOCA device according to specific properties.
    4. Open the device.
  4. Create all required DOCA core objects.
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    create_core_objects();

  5. Initiate DOCA core objects.
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    init_core_objects();

  6. Start host/DPU DMA copy.
    1. Host-side application:
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      host_start_dma_copy();

      1. Start negotiation with the DPU side application for the location and size of the file.
      2. Allocate memory for the DMA buffer.
      3. Export the memory map and send the output (export descriptor) to the DPU side application.
      4. Send the host local buffer memory address and length on the Comm Channel to the DPU side application.
      5. Wait for the DPU to notify that DMA Copy has ended.
      6. Close all memory objects.
      7. Clean resources.
    2. DPU-side application:
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      dpu_start_dma_copy();

      1. Start negotiation with the host side application for file location and size.
      2. Allocate memory for the DMA buffer.
      3. Receive the export descriptor on the Comm Channel.
      4. Create the DOCA memory map for the remote buffer on the host.
      5. Receive the host buffer information on the Comm Channel.
      6. Create two DOCA buffers, one for the remote (host) buffer and one for the local buffer.
      7. Submit the DMA job into the work queue.
      8. Send a host message to notify that DMA copy ended.
      9. Clean resources.
  7. Destroy Comm Channel.
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    destroy_cc();

  8. Destroy DOCA core objects.
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    destroy_core_objects();

  9. Arg parser destroy.
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    doca_argp_destroy();

The minimum required firmware version is 24.32.1010.

  1. Refer to the following documents:
  2. The DMA Copy example binary is located under /opt/mellanox/doca/applications/dma_copy/bin/doca_dma_copy. To build all the applications together, run:
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    cd /opt/mellanox/doca/applications/ meson build ninja -C build

  3. To build only the DMA Copy application:
    1. Edit the following flags in /opt/mellanox/doca/applications/meson_options.txt:
      • Set enable_all_applications to false
      • Set enable_dma_copy to true
    2. Run the commands in step 2.
      Note:

      doca_dma_copy will be created under ./build/dma_copy/src/.

    Application usage:

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    Usage: doca_dma_copy [DPDK Flags] -- [DOCA Flags] [Program Flags] DOCA Flags: -h, --help Print a help synopsis -v, --version Print program version information -l, --log-level Set the log level for the program <CRITICAL=20, ERROR=30, WARNING=40, INFO=50, DEBUG=60> Program Flags:   -f, --file Full path to file to be copied/created after a successful DMA copy -d, --dev-pci Comm Channel DOCA device PCI address -r, --rep-pci Comm Channel DOCA device representor PCI address


  4. Running the application on BlueField, CLI example:
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    /opt/mellanox/doca/applications/dma_copy/bin/doca_dma_copy -d 03:00.1 -r b1:00.1 -f /tmp/file_to_read.txt

  5. Running the application on the host, CLI example:
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    /opt/mellanox/doca/applications/dma_copy/bin/doca_dma_copy -d b1:00.1 -f /tmp/file_to_create.txt

    Note:

    Refer to section "Running DOCA Application on Host" in NVIDIA DOCA Virtual Functions User Guide.

  6. To run doca_dma_copy using a JSON file:
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    doca_dma_copy --json [json_file]

    For example:
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    cd /opt/mellanox/doca/applications/dma_copy/bin ./doca_dma_copy --json /root/dma_copy_params.json


Refer to NVIDIA DOCA Arg Parser User Guide for more information.

Flag Type Short Flag Long Flag/JSON Key Description JSON Content
General flags l log-level Set the log level for the application:
  • CRITICAL=20
  • ERROR=30
  • WARNING=40
  • INFO=50
  • DEBUG=60
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"log-level": 60

v version Print program version information N/A
h help Print a help synopsis N/A
Program flags f file Full path to file to be copied/created after a successful copy
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"file": "/tmp/sample.txt"

p dev-pci Comm Channel DOCA device PCIe address
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"dev-pci": "b1:00.0"

r rep-pci Comm Channel DOCA device representor PCIe address
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"rep-pci": "b1:02.0"

  • /opt/mellanox/doca/applications/dma_copy/src/dma_copy.c
  • /opt/mellanox/doca/applications/dma_copy/src/dma_copy_core.c
  • /opt/mellanox/doca/applications/dma_copy/src/dma_copy_core.h

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