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Advanced Features: Intel® Network Adapters User Guide

Flow Control
Interrupt Moderation Rate
IPv4 Checksum Offload
Jumbo Frames
Locally Administered Address
Offload TCP Segmentation
Priority & VLAN
Receive Buffers
Receive Side Scaling
Receive Side Scaling Queues
TCP Checksum Offload (IPv4)
Transmit Buffers
UDP Checksum Offload (IPv4)
Intel® I/O Acceleration Technology

NOTE: Intel® I/O Acceleration Technology (Intel® I/OAT) is not listed in the Advanced settings under the server properties tab of the adapter.

Setting Up Advanced Features in Microsoft Windows*

1. Open Microsoft Windows Device Manager.
2. Open Properties on your adapter.
3. Click the Advanced tab.
4. Select the Property you want to configure from the list of advanced features.
5. Select your desired setting (based on network capability).
6. Click OK to apply the changes.

Flow Control

Flow Control enables adapters to more effectively regulate traffic. Adapters generate flow control frames when their receive queues reach a pre-defined limit. Generating flow control frames signals the transmitter to slow transmission. Adapters respond to flow control frames by pausing packet transmission for the time specified in the flow control frame.

By enabling adapters to adjust packet transmission, flow control helps prevent dropped packets.

NOTE: For adapters to benefit from this feature, link partners must support flow control frames.

Interrupt Moderation Rate

Sets the Interrupt Throttle Rate (ITR). This setting moderates the rate at which Transmit and Receive interrupts are generated.

When an event such as packet receiving occurs, the adapter generates an interrupt. The interrupt interrupts the CPU and any application running at the time, and calls on the driver to handle the packet. At greater link speeds, more interrupts are created, and CPU rates also increase. This results in poor system performance. When you use a higher ITR setting, the interrupt rate is lower and the result is better CPU performance.

NOTE: A higher ITR rate also means that the driver has more latency in handling packets. If the adapter is handling many small packets, it is better to lower the ITR so that the driver can be more responsive to incoming and outgoing packets.

Altering this setting may improve traffic throughput for certain network and system configurations, however the default setting is optimal for common network and system configurations. Do not change this setting without verifying that the desired change will have a positive effect on network performance.

IPv4 Checksum Offload

This allows the adapter to compute the IPv4 checksum of incoming and outgoing packets. This feature enhances IPv4 receive and transmit performance and reduces CPU utilization.

With Offloading off, the operating system verifies the IPv4 checksum.

With Offloading on, the adapter completes the verification for the operating system.

Jumbo Frames

Jumbo frames are Ethernet frames that are larger than 1518 bytes. You can use Jumbo Frames to reduce server CPU utilization and increase throughput. However, additional latency may be introduced. The maximum size Jumbo Frame supported is 9014 bytes.

NOTE: End-to-end network hardware must support this capability, otherwise packets will be dropped.

To configure Jumbo Frames at the switch, consult your network administrator or switch user's guide.

Restrictions

• Supported protocols are limited to IP (TCP, UDP).
• Jumbo Frames require compatible switch connections that forward Jumbo Frames. Contact your switch vendor for more information.
• When standard sized Ethernet frames (64 to 1518 bytes) are used, there is no benefit to configuring Jumbo Frames.
• The Jumbo Frames setting on the switch must be set to at least 8 bytes larger than the adapter setting for Windows* operating systems, and at least 22 bytes larger for all other operating systems.

All equipment on the network must also support the larger frame size. When setting up Jumbo Frames on other network devices, be aware that different network devices calculate Jumbo Frame size differently. Some devices include the header information in the frame size while others do not. Intel adapters do not include header information in the frame size. When configuring Jumbo Frames on a switch, set the frame size four bytes higher for CRC, plus four bytes if you are using QoS packet tagging.  

Setting Up Jumbo Frames in Linux*

For information on configuring Jumbo Frames in Linux, see Linux Driver for the Intel® 10GbE Server Adapters.

Locally Administered Address

Overrides the initial MAC address with a user-assigned MAC address.

Offload TCP Segmentation

Allows the adapter hardware to segment data into valid Ethernet frames.

• With TCP Segmentation off, the operating system software segments the data before sending it to the adapter for transmission.
• With TCP Segmentation on, the adapter segments the data into frames.

Because the adapter hardware is able to complete data segmentation much faster than operating system software, this feature greatly increases transmission performance. In addition, the adapter consumes fewer CPU resources.

Priority & VLAN

Enables the adapter to offload inserting and removing priority and VLAN tags for transmit and receive.

Receive Buffers

Defines the number of Receive Buffers, which are data segments. They are allocated in the host memory and used to store the received packets. Each received packet requires at least one Receive Buffer, and each buffer uses 2KB of memory.

You might choose to increase the number of Receive Buffers if you notice a significant decrease in the performance of received traffic. If receive performance is not an issue, use the default setting appropriate to the adapter.

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.

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.

You must install Microsoft's Scalable Networking Pack (SNP) or Service Pack 2 (SP2) for RSS to function.

NOTE: The Scalable Networking Pack is part of Microsoft Windows Server 2003* Service Pack 2. It is not part of SP1 and requires a separate download. See http://www.microsoft.com for more information.

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.

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).

TCP Checksum Offload (IPv4)

This allows the adapter to verify the TCP checksum of incoming packets and compute the TCP checksum of outgoing packets. This feature enhances receive and transmit performance and reduces CPU utilization.

With Offloading off, the operating system verifies the TCP checksum.

With Offloading on, the adapter completes the verification for the operating system.

Transmit Buffers

Defines the number of Transmit Buffers, which are data segments that enable the adapter to track transmit packets in the system memory. Depending on the size of the packet, each transmit packet requires one or more Transmit Buffers.

You might choose to increase the number of Transmit Buffers if you notice a possible problem with transmit performance. Although increasing the number of Transmit Buffers can enhance transmit performance, Transmit Buffers do consume system memory. If transmit performance is not an issue, use the default setting. This default setting varies with the type of adapter.

UDP Checksum Offload (IPv4)

Allows the adapter to verify the UDP checksum of incoming packets and compute the UDP checksum of outgoing packets. This feature enhances receive and transmit performance and reduces CPU utilization.

With Offloading off, the operating system verifies the UDP checksum.

With Offloading on, the adapter completes the verification for the operating system.

Please read all restrictions and disclaimers.

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