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Support

Receive Side Scaling on Intel® Network Adapters


Last Reviewed: 18-Jan-2017
Article ID: 000006703

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 inefficient system cache utilization.

Note
  • This setting 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 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


RSS configuration
RSS is enabled on the Advanced tab of the adapter property sheet. If your adapter does not support RSS, or if your operating system does not support it, the RSS setting will not be displayed.


Teaming

  • 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 a non-Intel adapter is added to a team, RSS will automatically be disabled for the team.
  • Non-Intel adapters with RSS enabled cannot be added to a team


Known issues

On Windows Server 2012* configuring RSS for closest processor may cause transmit and receive failures
On Windows Server 2012 setting the "RSS load balancing profile" Advanced Setting to "Closest Processor" may significantly reduce CPU utilization. However, in some system configurations (such as a system with more Ethernet ports than processor cores), the "Closest Processor" setting may cause transmit and receive failures. Set *RSSProfile configuration to "NUMAScalingStatic" to work around this issue.

A supported hotfix is available from Microsoft. See
Incorrect RSS processor assignment on a Windows* 8 or Windows Server 2012-based computer that has multi-core processors*


Failed connection and possible system instability
If you have non-Intel networking devices capable of Receive-Side Scaling installed in your system, the Microsoft Windows registry keyword "RSSBaseCPU" may have been changed from the default value of 0x0 to point to a logical processor. If this keyword has been changed then devices based on Intel® 82598 or 82599 10 Gigabit Ethernet Controllers might not pass traffic. Attempting to make driver changes in this state may cause system instability. Set the value of RSSBaseCpu to 0x0, or to a value corresponding to a physical processor, and reboot the system to resolve the issue.


Receive Side Scaling value is blank
Changing the Receive Side Scaling setting of an adapter in a team may cause the value for that setting to appear blank when you next check it. It may also appear blank for the other adapters in the team. The adapter may be unbound from the team in this situation. Disabling and enabling the team will resolve the issue.


CPU utilization higher than expected
Setting RSS Queues to a value greater than 4 is only advisable for large web servers with several processors. Values greater than 4 may increase CPU utilization to unacceptable levels and have other negative impacts on system performance.
 

Related topics
User Guides for Intel® Ethernet Adapters
Incorrect RSS processor assignment on a Windows* 8 or Windows Server 2012-based computer that has multi-core processors
 
 
 

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