User Guide

Receive Side Scaling
When Receive Side Scaling (RSS) is enabled, all of the receive data processing for a particular TCP
connection is shared across multiple processors or processor cores. Without RSS all of the 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
LAN RSS applies to a particular TCP connection.
NOTE: This setting has no effect if your system has only one processing unit.
LAN RSS Configuration
RSS is enabled on the Advanced tab of the adapter property sheet. If your adapter does not support RSS, or
if the SNP or SP2 is not installed, the RSS setting will not be displayed. If RSS is supported in your system
environment, the following will be displayed:
l Port NUMA Node. This is the NUMA node number of a device.
l Starting RSS CPU. This setting allows you to set the p referred starting RSS processor. Change this
setting if the current processor is dedicated to other processes. The setting range is from 0 to the num-
ber of logical CPUs - 1. In Server 2008 R2, RSS will only use CPUs in group 0 (CPUs 0 through 63).
l Max number of RSS CPU. This setting allows you to set the maximum number of CPUs assigned to
an adapter and is primarily used in a Hyper-V environment. By decreasing this setting in a Hyper-V
environment, the total number of interrupts is reduced which lowers CPU utilization. The default is 8 for
Gigabit adapters and 16 for 10 Gigabit adapters.
l Preferred NUMA Node. This setting 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 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.
NOTES:
l This setting only affects NUMA systems. It will have no effect on non-NUMA sys-
tems.
l Choosing a value greater than the number of NUMA nodes present in the system
selects the NUMA node closest to the device.
l Receive Side Scaling Queues. This setting configures the number of RSS queues, which determine
the space to buffer transactions between the network adapter and CPU(s).
Default 2 queues for the Intel® 10 Gigabit Server Adapters
Range l 1 queue is used when low CPU utilization is required.
l 2 queues are used when good throughput and low CPU utilization are required.
l 4 queues are used for applications that demand maximum throughput and
transactions per second.