The phrase “Receive Side Scaling” (RSS) refers to the idea that all receive data processing is shared (scaled) across multiple processors or processor cores. Without RSS all receive data processing is performed by a single processor, resulting in less efficient system cache utilization.
RSS can be enabled for a LAN or for FCoE. In the first case, it is called “LAN RSS”. In the second, it is called “FCoE RSS”.
LAN RSS applies to a particular TCP connection. Note the following:
RSS has no effect if your system has only one processing unit.
RSS must be enabled for Intel® I/O Acceleration Technology to function.
To enable RSS on Microsoft* Windows Server* 2003, you must install Microsoft's Scalable Networking Pack. The Scalable Networking Pack is part of Windows Server 2003 SP2. It is not included in SP1 and requires a separate download. See http://www.microsoft.com for more information.
RSS is not supported on some adapters configured to use Virtual Machine Queues (VMQ). On these adapters VMQ will take precedence over RSS. RSS will appear disabled.
LAN RSS is enabled on the Advanced tab of the adapter property sheet. If your adapter or operating system does not support it, the RSS settings will not be displayed. If your adapter does support it, the following settings will be displayed:
Port NUMA Node: the NUMA node number of a device.
Receive Side Scaling Queues: allocates queue space to buffer transactions between the network adapter and CPU(s). Range:
1 queue is used when low CPU utilization is required.
2 queues are used when good throughput and low CPU utilization are required.
4 or more queues are used for applications that demand maximum throughput and
Starting RSS CPU: allows you to set the preferred starting LAN RSS processor. Change this setting if the current processor is dedicated to other processes. The setting range is from 0 to the number of logical CPUs - 1. In Server 2008 R2, LAN RSS will only use CPUs in group 0 (CPUs 0 through 63).
Preferred NUMA Node: allows you to choose the preferred NUMA (Non-Uniform Memory Access) node to be used for memory allocations made by the network adapter. In addition the system will attempt to use the CPUs from the preferred NUMA node first for the purposes of LAN RSS. On NUMA platforms, memory access latency is dependent on the memory location. Allocation of memory from the closest node helps improve performance. The Windows Task Manager shows the NUMA Node ID for each processor. Note that this setting only affects NUMA systems; it will have no effect on non-NUMA systems.
If RSS is not enabled for all adapters in a team, RSS will automatically be disabled for the team. If an adapter that does not support RSS is added to a team, RSS will automatically be disabled for the team. If you create a Multi-Vendor Team, you must manually verify that the RSS settings for all adapters in the team are the same.
If FCoE is installed, FCoE RSS is enabled and applies to FCoE receive processing that is shared across processor cores.
If your adapter supports FCoE RSS, the following configuration settings can be viewed and changed on the Performance Options of the Advanced tab of the Network Adapter device properties: