SplitRx mode uses multiple physical CPUs to process network packets received in a single network queue. This feature can significantly improve network performance for certain workloads. These workloads include:

  • Multiple virtual machines on one VMware Cloud on AWS host all receiving multicast traffic from the same source. (SplitRx mode will typically improve throughput and CPU efficiency for these workloads.)

  • Traffic via the vSphere Network Appliance API (DvFilter) between two virtual machines on the same host. (SplitRx mode will typically improve throughput and maximum packet rates for these workloads.)

This feature is automatically activated for a VMXNET3 virtual network adapter (the only adapter type on which it is supported) when VMware Cloud on AWS detects that a single network queue on a physical NIC is both (a) heavily utilized and (b) getting more than 10,000 broadcast/multicast packets per second.

Note:

SplitRx mode will be automatically activated as described above only if the network traffic is coming in over a physical NIC, not when the traffic is entirely internal to the VMware Cloud on AWS host. In cases where the traffic is entirely internal, however, SplitRx mode can be manually activated if desired, as described in "Activating or Deactivating SplitRx Mode for an Individual Virtual NIC," below.

Activating or Deactivating SplitRx Mode for an Individual Virtual NIC

The SplitRx mode feature can be individually configured for each virtual NIC (overriding the global NetSplitRxMode setting) using the ethernetX.emuRxMode variable for each virtual machine (where X is replaced with the network adapter’s ID).

The possible values for this variable are:

  • ethernetX.emuRxMode = "0"

    This value deactivates splitRx mode for ethernetX.

  • ethernetX.emuRxMode = "1"

    This value activates splitRx mode for ethernetX.

To change this variable through the vSphere Client:

  1. Right-click the virtual machine you wish to change, then select Edit Settings.

  2. Under the VM Options tab, expand Advanced, then click EDIT CONFIGURATION.

  3. Look for ethernetX.emuRxMode (where X is the number of the desired NIC) and configure it as you wish. If the variable isn’t present, click ADD CONFIGURATION PARAMS and enter it as a new parameter.

  4. Click OK to close the Configuration Parameters window.

  5. Click OK to close the Edit Settings window.

The change will not take effect until the virtual machine has been restarted or the relevant vNIC is disconnected from the virtual machine and connected again.