Dynamic Interrupt Moderation

Dynamic Interrupt Moderation (DIM) adjusts the interrupt moderation settings to optimize packet processing. For guest OS kernels older than version 6.8, DIM offloads this function to the DPU, reducing the interrupt rate from the guest OS.

By lowering the interrupt rate in high-bandwidth traffic scenarios, DIM enhances CPU utilization for both the hypervisor and guest VMs, while maintaining nearly the same bandwidth.

For example, the following table shows the benefit of using DIM:

The following test parameters:

• Guest OS kernel version – 5.11.0

• Number of virtio-net device – 1

• Number of QPs – 31

• Queue depth – 1024

• MTU – 1500

• Benchmark – iPerf with 31 streams

DIM is a per-device configuration. To enable or disable it, use this command:

            

            
[dpu]# virtnet modify -p <pf> [-v <vf>] device -dim {enable | disable}
        

Configuration example:

1. Unload drivers from the guest-OS side:

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   [host]# modprobe -rv virtio_net && modprobe -rv virtio_pci
           

2. Enable DIM:

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   [dpu]# virtnet modify -p 0 device -dim enable
   {'pf': '0x0', 'all': '0x0', 'subcmd': '0x0', 'dim_config': 'enable'}
   {
     "errno": 0,
     "errstr": "Success"
   }
           

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   Using disable disables DIM.

3. Load the drivers:

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   [host]# modprobe -v virtio_pci && modprobe -v virtio_net
           

4. Query the device to verify dim is enabled:

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   [dpu]# virtnet query -p 0 -b | grep -i dim
         "dim": "enabled"