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FWIW, you should be able to measure the effect of the Interrupt Moderation setting by looking at CPU use when network activity is high. If your CPU load is already high while running SC, disabling Interrupt Moderation may make things worse. It's important to look at single-CPU load, though, since interrupts are only processed on one CPU.
Nov 1, 2021 · Performance options - Interrupt moderation rate. Sets the Interrupt Throttle Rate (ITR), the rate at which the controller moderates interrupts. The default setting is optimized for common configurations. Changing this setting can improve network performance on certain network and system configurations.
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- Overview
- Enabling offload features
- Enabling receive-side scaling (RSS) for web servers
- Increasing network adapter resources
- Performance tuning for low-latency packet processing
- System management interrupts
- Performance tuning TCP
Use the information in this topic to tune the performance network adapters for computers that are running Windows Server 2016 and later versions. If your network adapters provide tuning options, you can use these options to optimize network throughput and resource usage.
The correct tuning settings for your network adapters depend on the following variables:
•The network adapter and its feature set
•The type of workload that the server performs
•The server hardware and software resources
•Your performance goals for the server
Turning on network adapter offload features is usually beneficial. However, the network adapter might not be powerful enough to handle the offload capabilities with high throughput.
Important
Do not use the offload features IPsec Task Offload or TCP Chimney Offload. These technologies are deprecated in Windows Server 2016, and might adversely affect server and networking performance. In addition, these technologies might not be supported by Microsoft in the future.
For example, consider a network adapter that has limited hardware resources. In that case, enabling segmentation offload features might reduce the maximum sustainable throughput of the adapter. However, if the reduced throughput is acceptable, you should go ahead an enable the segmentation offload features.
RSS can improve web scalability and performance when there are fewer network adapters than logical processors on the server. When all the web traffic is going through the RSS-capable network adapters, the server can process incoming web requests from different connections simultaneously across different CPUs.
Important
Avoid using both non-RSS network adapters and RSS-capable network adapters on the same server. Because of the load distribution logic in RSS and Hypertext Transfer Protocol (HTTP), performance might be severely degraded if a non-RSS-capable network adapter accepts web traffic on a server that has one or more RSS-capable network adapters. In this circumstance, you should use RSS-capable network adapters or disable RSS on the network adapter properties Advanced Properties tab.
To determine whether a network adapter is RSS-capable, you can view the RSS information on the network adapter properties Advanced Properties tab.
For network adapters that allow you to manually configure resources such as receive and send buffers, you should increase the allocated resources.
Some network adapters set their receive buffers low to conserve allocated memory from the host. The low value results in dropped packets and decreased performance. Therefore, for receive-intensive scenarios, we recommend that you increase the receive buffer value to the maximum.
Many network adapters provide options to optimize operating system-induced latency. Latency is the elapsed time between the network driver processing an incoming packet and the network driver sending the packet back. This time is usually measured in microseconds. For comparison, the transmission time for packet transmissions over long distances is usually measured in milliseconds (an order of magnitude larger). This tuning will not reduce the time a packet spends in transit.
Following are some performance tuning suggestions for microsecond-sensitive networks.
•Set the computer BIOS to High Performance, with C-states disabled. However, note that this is system and BIOS dependent, and some systems will provide higher performance if the operating system controls power management. You can check and adjust your power management settings from Settings or by using the powercfg command. For more information, see Powercfg Command-Line Options.
•Set the operating system power management profile to High Performance System.
•Enable static offloads. For example, enable the UDP Checksums, TCP Checksums, and Send Large Offload (LSO) settings.
•If the traffic is multi-streamed, such as when receiving high-volume multicast traffic, enable RSS.
Many hardware systems use System Management Interrupts (SMI) for a variety of maintenance functions, such as reporting error correction code (ECC) memory errors, maintaining legacy USB compatibility, controlling the fan, and managing BIOS-controlled power settings.
The SMI is the highest-priority interrupt on the system, and places the CPU in a management mode. This mode preempts all other activity while SMI runs an interrupt service routine, typically contained in BIOS.
Unfortunately, this behavior can result in latency spikes of 100 microseconds or more.
If you need to achieve the lowest latency, you should request a BIOS version from your hardware provider that reduces SMIs to the lowest degree possible. These BIOS versions are frequently referred to as "low latency BIOS" or "SMI free BIOS." In some cases, it is not possible for a hardware platform to eliminate SMI activity altogether because it is used to control essential functions (for example, cooling fans).
TCP receive window autotuning
In Windows Vista, Windows Server 2008, and later versions of Windows, the Windows network stack uses a feature that is named TCP receive window autotuning level to negotiate the TCP receive window size. This feature can negotiate a defined receive window size for every TCP communication during the TCP Handshake. In earlier versions of Windows, the Windows network stack used a fixed-size receive window (65,535 bytes) that limited the overall potential throughput for connections. The total achievable throughput of TCP connections could limit network usage scenarios. TCP receive window autotuning enables these scenarios to fully use the network. For a TCP receive window that has a particular size, you can use the following equation to calculate the total throughput of a single connection. For example, for a connection that has a latency of 10 ms, the total achievable throughput is only 51 Mbps. This value is reasonable for a large corporate network infrastructure. However, by using autotuning to adjust the receive window, the connection can achieve the full line rate of a 1-Gbps connection. Some applications define the size of the TCP receive window. If the application does not define the receive window size, the link speed determines the size as follows: •Less than 1 megabit per second (Mbps): 8 kilobytes (KB) •1 Mbps to 100 Mbps: 17 KB •100 Mbps to 10 gigabits per second (Gbps): 64 KB •10 Gbps or faster: 128 KB For example, on a computer that has a 1-Gbps network adapter installed, the window size should be 64 KB. This feature also makes full use of other features to improve network performance. These features include the rest of the TCP options that are defined in RFC 1323. By using these features, Windows-based computers can negotiate TCP receive window sizes that are smaller but are scaled at a defined value, depending on the configuration. This behavior the sizes easier to handle for networking devices. Review and configure TCP receive window autotuning level You can use either netsh commands or Windows PowerShell cmdlets to review or modify the TCP receive window autotuning level. To use netsh to review or modify the autotuning level To review the current settings, open a Command Prompt window and run the following command: The output of this command should resemble the following: To modify the setting, run the following command at the command prompt: For more information about this command, see Netsh commands for Interface Transmission Control Protocol. To use Powershell to review or modify the autotuning level To review the current settings, open a PowerShell window and run the following cmdlet. The output of this cmdlet should resemble the following. To modify the setting, run the following cmdlet at the PowerShell command prompt. For more information about these cmdlets, see the following articles: •Get-NetTCPSetting •Set-NetTCPSetting Autotuning levels You can set receive window autotuning to any of five levels. The default level is Normal. The following table describes the levels. If you use an application to capture network packets, the application should report data that resembles the following for different window autotuning level settings. •Autotuning level: Normal (default state) •Autotuning level: Disabled •Autotuning level: Restricted •Autotuning level: Highly restricted •Autotuning level: Experimental Deprecated TCP parameters The following registry settings from Windows Server 2003 are no longer supported, and are ignored in later versions. •TcpWindowSize •NumTcbTablePartitions •MaxHashTableSize Review and configure TCP receive window autotuning level You can use either netsh commands or Windows PowerShell cmdlets to review or modify the TCP receive window autotuning level. To use netsh to review or modify the autotuning level To review the current settings, open a Command Prompt window and run the following command:e output of this command should resemble the following: modify the setting, run the following command at the command prompt:Note In the preceding command, represents the new value for the auto tuning level. For more information about this command, see Netsh commands for Interface Transmission Control Protocol. To use Powershell to review or modify the autotuning level To review the current settings, open a PowerShell window and run the following cmdlet.e output of this cmdlet should resemble the following. modify the setting, run the following cmdlet at the PowerShell command prompt.For more information about these cmdlets, see the following articles: •Get-NetTCPSetting •Set-NetTCPSetting
The following command disables adaptive interrupt moderation and allows a maximum of 5 microseconds before indicating a receive or transmit was complete. Instead of resulting in as many as 200,000 interrupts per second, it limits total interrupts per second to 50,000 via the rx-usecs-high parameter. # ethtool -C < ethX > adaptive-rx off ...
For PCI and PCI-X*, install the Intel Network Adapter in the fastest available slot. Example 1: If you have a 64-bit PCI adapter, put it in a 66 MHz 64-bit PCI slot. Example 2: If you have a 64-bit PCI-X adapter, put in a 133 MHz (266 or 533 if available) 64-bit PCI-X slot. The slowest board on a bus dictates the maximum speed of the bus.
Double-click Network adapters. Right-click the network adapter you want, and then click Properties. On the Advanced tab, Look for energy-saving options and make the appropriate changes you want. For changing this setting on an Ethernet switch, refer to the Ethernet switch specific power saving options and make the appropriate changes you want. 4.
Interrupt Moderation. Adaptive interrupt moderation is on by default, and is designed to provide a balanced approach between low CPU utilization and high performance. However, you might try tuning interrupt settings manually to fit your use case. The range of 0-235 microseconds provides an effective range of 4,310 to 250,000 interrupts per ...
