Mastering Windows Server 2016 Hyper-V

processor core.

For vRSS, the network adapter must support VMQ. The actual RSS work is performed
on the Hyper-V host within the Hyper-V switch. Therefore, using vRSS does introduce
some additional CPU load on the host, which is why, by default, vRSS is disabled in
the virtual machine. It must be enabled within the virtual machine the same way
regular RSS would be enabled on a physical host:

1 . Use the Enable-NetAdapterRss    PowerShell  cmdlet.

2 . Within  the properties  of  the virtual network adapter inside  the virtual machine,

select  the Advanced    tab and set the Receive Side    Scaling property    to  Enabled.

With vRSS enabled, once the processor core processing the network traffic is utilizing
around 80 percent, the processing will start to be distributed among multiple vCPUs.

A great way to show and maximize the throughput of a network adapter is by using
Microsoft’s ntttcp.exe test tool, which allows multiple streams to be created as a
sender and receiver, therefore maximizing the use of a network connection. The tool
can be downloaded from the following location:
http://gallery.technet.microsoft.com/NTttcp-Version-528-Now-f8b12769

Once it’s downloaded, copy ntttcp.exe into a virtual machine (with at least four
vCPUs and with its firewall disabled) that is connected to a virtual switch using a
10Gbps network adapter (this will receive the traffic) and to a physical host with a
10Gbps network adapter (this will send the traffic). Within the virtual machine, run
the tool as follows:

Ntttcp.exe -r -m 16,*, ‐a 16 ‐t 10

This command puts the virtual machine in a listening mode, waiting for the traffic to
arrive. On the physical host, send the traffic by using the following command:

Ntttcp.exe -s -m 16,*, ‐a 16 ‐t 10

The virtual machine will show that traffic is being received. Open Task Manager and
view the CPU in the Performance tab. Ensure that the CPU graph is set to Logical
Processors (right-click the process graph, and select Change Graph To ➣ Logical
Processors). Initially, without vRSS, the bandwidth will likely be around 4 to 5Gbps
(depending on the speed of your processor cores, but most important, only a single
vCPU will be utilized). Then turn on vRSS within the VM and run the test again. This
time the bandwidth will be closer to 10Gbps, and many of the vCPUs will be utilized.
This really shows the benefit of vRSS, and in Figure 3.40 and Figure 3.41, you can see
my performance view without and with vRSS. Notice both the processor utilization
and the network speed.