RSC in the vSwitch

Applies to: Windows Server 2019

Receive Segment Coalescing (RSC) in the vSwitch is a feature in Windows Server 2019 and Windows 10 October 2018 Update that helps reduce host CPU utilization and increases throughput for virtual workloads by coalescing multiple TCP segments into fewer, but larger segments. Processing fewer, large segments (coalesced) is more efficient than processing numerous, small segments.

Windows Server 2012 and later included a hardware-only offload version (implemented in the physical network adapter) of the technology also known as Receive Segment Coalescing. This offloaded version of RSC is still available in later versions of Windows. However, it is incompatible with virtual workloads and was disabled once a physical network adapter is attached to a vSwitch. For more information on the hardware-only version of RSC, see Receive Segment Coalescing (RSC).

Scenarios that benefit from RSC in the vSwitch

Workloads whose datapath traverses a virtual switch benefits from this feature.

For example:

  • Host Virtual NICs including:

    • Software Defined Networking

    • Hyper-V Host

    • Storage Spaces Direct

  • Hyper-V Guest Virtual NICs

  • Software Defined Networking GRE Gateways

  • Container

Workloads that are not compatible with this feature include:

  • Software Defined Networking IPSEC Gateways

  • SR-IOV enabled virtual NICs

  • SMB Direct

Configure RSC in the vSwitch

By default, on external vSwitches, RSC is enabled.

View the current settings:

Get-VMSwitch -Name vSwitchName | Select-Object *RSC*

Enable or Disable RSC in the vSwitch

Important

Important: RSC in the vSwitch can be enabled and disabled on the fly without impact to existing connections.

Disable RSC in the vSwitch

Set-VMSwitch -Name vSwitchName -EnableSoftwareRsc $false

Re-enable RSC in the vSwitch

Set-VMSwitch -Name vSwitchName -EnableSoftwareRsc $True

For more information, see Set-VMSwitch.