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In this article, you will learn how to test the physical state of the InfiniBand™ connection. The guides below will help you to check that InfiniBand connections are established between GPUs in a GPU cluster.

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Testing the port state

  1. Connect to the VM using SSH.
  2. In the VM’s shell, run ibstatus command that displays operational information about InfiniBand network devices. Result: 
    Infiniband device 'mlx5_0' port 1 status:
   default gid:    fe80:0000:0000:0000:****:****:****:03c5
   base lid:    0x***
   sm lid:      0x*
   state:       4: ACTIVE
   phys state:  5: LinkUp
   rate:     400 Gb/sec (4X NDR)
   link_layer:  InfiniBand

Infiniband device 'mlx5_1' port 1 status:
   default gid:    fe80:0000:0000:0000:****:****:****:03c6
   base lid:    0x***
   sm lid:      0x*
   state:       4: ACTIVE
   phys state:  5: LinkUp
   rate:     400 Gb/sec (4X NDR)
   link_layer:  InfiniBand
...
  3. For each device in the result, check the physical state (phys state): it should be LinkUp.

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Testing network performance

You can also emulate the network activity by sending some data from GPUs on one VM to GPUs on another:
  1. Install the perftest package on each one of the test VMs: 
    sudo apt install perftest
  2. Connect to the first VM using SSH.
  3. Run ib_send_bw --report_gbits.
  4. Copy the first VM’s private IP address.
  5. Connect to the second VM using SSH.
  6. Run ib_send_bw <first_VM_IP_address> --report_gbits.
In the commands output, you should see non-zero values for the bytes sent, average bandwith speed, and average message rate. The bandwidth peak speed might not reach the theoretical maximum 400 Gbps. Example: 
+--------------------------------------------------------------------------------+
| #bytes   #iterations   #BW peak[Gb/sec]   #BW average[Gb/sec]   #MsgRate[Mpps] |
+--------------------------------------------------------------------------------+
| 65536    1000          360.39             359.91                0.686466       |
+--------------------------------------------------------------------------------+
See also
InfiniBand and InfiniBand Trade Association are registered trademarks of the InfiniBand Trade Association.