• Tcp Windows Auto Tuning
• Tcp Receive Window Auto Tuning Windows 2012 Key
• Tcp Receive Window Auto-tuning Windows 2012
• Auto Tuning Video
• Tcp Receive Window Size
• Tcp Receive Window Auto Tuning Windows 2012 Free

• The Receive Window Auto-Tuning feature lets the operating system continually monitor routing conditions such as bandwidth, network delay, and application delay. Therefore, the operating system can configure connections by scaling the TCP receive window to maximize the network performance.
• How to disable TCP chimney offloading and receive window autotuning in Windows Server, which may improve iSCSI network performance. TCP chimney offloading and receive window auto-tuning are frequently disabled as part of the process of troubleshooting a network-related issue on a Windows.
• Mar 28, 2019  Windows 10 optimized features in the TCP/IP stack, including CTCP, and TCP Window Auto-Tuning. The new implementation works much better by default than previous Windows versions with broadband internet connections and is able to adjust many values on the automatically.

Applies To: Windows Server 2012

This topic contains the following sections.

Determining the correct tuning settings for your network adapter depend on the following variables:

• /vst-crack-shut-down.html. The network adapter and its feature set

• The type of workload performed by the server

• The server hardware and software resources

• Your performance goals for the server

By default, Windows in normal auto tuning level will use RWIN size of 256 bytes with a scale factor of 8. This value is not suitable for all routers and servers which does not support TCP scale factor, and continue to communicate with 65536 bytes (64kB). 64kB is the fixed default TCP receive buffer, and through autotuning it can scale up to 16 MB.

If your network adapter provides tuning options, you can optimize network throughput and resource usage to achieve optimum throughput based on the parameters described above.

The following sections describe some of your performance tuning options.

Enabling Offload Features

Turning on network adapter offload features is usually beneficial. Sometimes, however, the network adapter is not powerful enough to handle the offload capabilities with high throughput. For example, enabling segmentation offload can reduce the maximum sustainable throughput on some network adapters because of limited hardware resources. However, if the reduced throughput is not expected to be a limitation, you should enable offload capabilities, even for this type of network adapter.

Note

Some network adapters require offload features to be independently enabled for send and receive paths.

Enabling Receive Side Scaling (RSS) for Web Servers

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, incoming web requests from different connections can be simultaneously processed across different CPUs.

It is important to note that due to the logic in RSS and Hypertext Transfer Protocol (HTTP) for load distribution, 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.

RSS Profiles and RSS Queues

RSS predefined profiles are new in Windows Server 2012.

The default profile is NUMA Static, which changes the default behavior from previous versions of the operating system. To get started with RSS Profiles, you can review the available profiles to understand when they are beneficial and how they apply to your network environment and hardware.

For example, if you open Task Manager and review the logical processors on your server, and they seem to be underutilized for receive traffic, you can try increasing the number of RSS queues from the default of 2 to the maximum that is supported by your network adapter. Your network adapter might have options to change the number of RSS queues as part of the driver.

Increasing Network Adapter Resources

For network adapters that allow manual configuration of 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.

Note

If a network adapter does not expose manual resource configuration, it either dynamically configures the resources, or the resources are set to a fixed value that cannot be changed.

Enabling Interrupt Moderation

To control interrupt moderation, some network adapters expose different interrupt moderation levels, buffer coalescing parameters (sometimes separately for send and receive buffers), or both.

You should consider interrupt moderation for CPU-bound workloads, and consider the trade-off between the host CPU savings and latency versus the increased host CPU savings because of more interrupts and less latency. If the network adapter does not perform interrupt moderation, but it does expose buffer coalescing, increasing the number of coalesced buffers allows more buffers per send or receive, which improves performance.

Performance Tuning for Low Latency Packet Processing

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 Control Panel 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. Note that this will not work properly if the system BIOS has been set to disable operating system control of power management.

• Enable Static Offloads, for example, UDP Checksums, TCP Checksums, and Send Large Offload (LSO).

• Enable RSS if the traffic is multi-streamed, such as high-volume multicast receive.

• Disable the Interrupt Moderation setting for network card drivers that require the lowest possible latency. Remember, this can use more CPU time and it represents a tradeoff.

• Handle network adapter interrupts and DPCs on a core processor that shares CPU cache with the core that is being used by the program (user thread) that is handling the packet. CPU affinity tuning can be used to direct a process to certain logical processors in conjunction with RSS configuration to accomplish this. Using the same core for the interrupt, DPC, and user mode thread exhibits worse performance as load increases because the ISR, DPC, and thread contend for the use of the core.

System Management Interrupts

Many hardware systems use System Management Interrupts (SMI) for a variety of maintenance functions, including reporting of error correction code (ECC) memory errors, legacy USB compatibility, fan control, and BIOS controlled power management. The SMI is the highest priority interrupt on the system and places the CPU in a management mode, which preempts all other activity while it runs an interrupt service routine, typically contained in BIOS.

Unfortunately, this 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 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).

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Note

The operating system can exert no control over SMIs because the logical processor is running in a special maintenance mode, which prevents operating system intervention.

Tcp Receive Window Auto Tuning Windows 2012 Key

Performance Tuning TCP

You can performance tune TCP using the following items.

Details are provided in the following sections.

TCP Receive Window Auto-Tuning

Prior to Windows Server 2008, the network stack used a fixed-size receive-side window that limited the overall potential throughput for connections. /shop-cooking-games-download.html. One of the most significant changes to the TCP stack is TCP receive window auto-tuning. You can calculate the total throughput of a single connection when you use this fixed size default as:

Total achievable throughput in bytes = TCP window * (1 / connection latency)

For example, the total achievable throughput is only 51 Mbps on a 1 GB connection with 10 ms latency – which is a reasonable value for a large corporate network infrastructure.

With auto-tuning, however, the receive-side window is adjustable, and it can grow to meet the demands of the sender. It is entirely possible for a connection to achieve the full line rate of a 1 GB connection. Network usage scenarios that might have been limited in the past by the total achievable throughput of TCP connections can now fully use the network.

Windows Filtering Platform

The Windows Filtering Platform (WFP) that was introduced in Windows Vista and Windows Server 2008 provides APIs to non-Microsoft independent software vendors (ISVs) to create packet processing filters. Examples include firewall and antivirus software.

Note

A poorly written WFP filter can significantly decrease a server’s networking performance.

For more information, see Windows Filtering Platform in the Windows Dev Center.

TCP Parameters

The following registry keywords from Windows Server 2003 are no longer supported, and they are ignored in Windows Server 2012, Windows Server 2008 R2, and Windows Server 2008.

• TcpWindowSize

• NumTcbTablePartitions

• MaxHashTableSize

TCP tuning techniques adjust the network congestion avoidance parameters of Transmission Control Protocol (TCP) connections over high-bandwidth, high-latency networks. Well-tuned networks can perform up to 10 times faster in some cases.^[1] However, blindly following instructions without understanding their real consequences can hurt performance as well.

Network and system characteristics[edit]

Bandwidth-delay product (BDP)[edit]

Bandwidth-delay product (BDP) is a term primarily used in conjunction with TCP to refer to the number of bytes necessary to fill a TCP 'path', i.e. it is equal to the maximum number of simultaneous bits in transit between the transmitter and the receiver.

Tcp Receive Window Auto-tuning Windows 2012

High performance networks have very large BDPs. To give a practical example, two nodes communicating over a geostationary satellite link with a round-trip delay time (or round-trip time, RTT) of 0.5 seconds and a bandwidth of 10 Gbit/s can have up to 0.5×10¹⁰bits, i.e., 5 Gbit = 625 MB of unacknowledged data in flight. Despite having much lower latencies than satellite links, even terrestrial fiber links can have very high BDPs because their link capacity is so large. Operating systems and protocols designed as recently as a few years ago when networks were slower were tuned for BDPs of orders of magnitude smaller, with implications for limited achievable performance.

Buffers[edit]

The original TCP configurations supported TCP receive window sizebuffers of up to 65,535 (64 KiB - 1) bytes, which was adequate for slow links or links with small RTTs. Larger buffers are required by the high performance options described below.

Buffering is used throughout high performance network systems to handle delays in the system. In general, buffer size will need to be scaled proportionally to the amount of data 'in flight' at any time. For very high performance applications that are not sensitive to network delays, it is possible to interpose large end to end buffering delays by putting in intermediate data storage points in an end to end system, and then to use automated and scheduled non-real-time data transfers to get the data to their final endpoints.

TCP speed limits[edit]

Maximum achievable throughput for a single TCP connection is determined by different factors. One trivial limitation is the maximum bandwidth of the slowest link in the path. But there are also other, less obvious limits for TCP throughput. Bit errors can create a limitation for the connection as well as RTT.

Window size[edit]

In computer networking, RWIN (TCP Receive Window) is the amount of data that a computer can accept without acknowledging the sender. If the sender has not received acknowledgement for the first packet it sent, it will stop and wait and if this wait exceeds a certain limit, it may even retransmit. This is how TCP achieves reliable data transmission.

Even if there is no packet loss in the network, windowing can limit throughput. Because TCP transmits data up to the window size before waiting for the acknowledgements, the full bandwidth of the network may not always get used. The limitation caused by window size can be calculated as follows:

${\displaystyle \mathrm{T}\mathrm{h}\mathrm{r}\mathrm{o}\mathrm{u}\mathrm{g}\mathrm{h}\mathrm{p}\mathrm{u}\mathrm{t}\le \frac{\mathrm{R}\mathrm{W}\mathrm{I}\mathrm{N}}{\mathrm{R}\mathrm{T}\mathrm{T}}}$

where RWIN is the TCP Receive Window and RTT is the round-trip time for the path.

At any given time, the window advertised by the receive side of TCP corresponds to the amount of free receive memory it has allocated for this connection. Otherwise it would risk dropping received packets due to lack of space.

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The sending side should also allocate the same amount of memory as the receive side for good performance. That is because, even after data has been sent on the network, the sending side must hold it in memory until it has been acknowledged as successfully received, just in case it would have to be retransmitted. If the receiver is far away, acknowledgments will take a long time to arrive. If the send memory is small, it can saturate and block emission. A simple computation gives the same optimal send memory size as for the receive memory size given above.

Packet loss[edit]

When packet loss occurs in the network, an additional limit is imposed on the connection.^[2] In the case of light to moderate packet loss when the TCP rate is limited by the congestion avoidance algorithm, the limit can be calculated according to the formula (Mathis, et al.):

${\displaystyle \mathrm{T}\mathrm{h}\mathrm{r}\mathrm{o}\mathrm{u}\mathrm{g}\mathrm{h}\mathrm{p}\mathrm{u}\mathrm{t}\le \frac{\mathrm{M}\mathrm{S}\mathrm{S}}{\mathrm{R}\mathrm{T}\mathrm{T}\sqrt{P_{\mathrm{l}\mathrm{o}\mathrm{s}\mathrm{s}}}}}$

where MSS is the maximum segment size and P_loss is the probability of packet loss. If packet loss is so rare that the TCP window becomes regularly fully extended, this formula doesn't apply.

TCP options for high performance[edit]

A number of extensions have been made to TCP over the years to increase its performance over fast high-RTT links ('long fat networks' or LFNs).

Tcp Receive Window Size

TCP timestamps (RFC 1323) play a double role: they avoid ambiguities due to the 32-bit sequence number field wrapping around, and they allow more precise RTT estimation in the presence of multiple losses per RTT. With those improvements, it becomes reasonable to increase the TCP window beyond 64 kB, which can be done using the window scaling option (RFC 1323).

The TCP selective acknowledgment option (SACK, RFC 2018) allows a TCP receiver to precisely inform the TCP sender about which segments have been lost. This increases performance on high-RTT links, when multiple losses per window are possible.

Path MTU Discovery avoids the need for in-network fragmentation, increasing the performance in the presence of packet loss.

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See also[edit]

References[edit]

1. ^'High Performance SSH/SCP - HPN-SSH'. Psc.edu. Retrieved January 23, 2020.
2. ^'The Macroscopic Behavior of the TCP Congestion Avoidance Algorithm'. Psc.edu. Archived from the original on May 11, 2012. Retrieved January 3, 2017.

External links[edit]

• RFC 1323 - TCP Extensions for High Performance
• RFC 2018 - TCP Selective Acknowledgment Options
• RFC 2582 - The NewReno Modification to TCP's Fast Recovery Algorithm
• RFC 2488 - Enhancing TCP Over Satellite Channels using Standard Mechanisms
• RFC 2883 - An Extension to the Selective Acknowledgment (SACK) Option for TCP
• RFC 3517 - A Conservative Selective Acknowledgment-based Loss Recovery Algorithm for TCP
• RFC 4138 - Forward RTO-Recovery (F-RTO): An Algorithm for Detecting Spurious Retransmission Timeouts with TCP and the Stream Control Transmission Protocol (SCTP)
• TCP Tuning Guide, ESnet
• DrTCP - a utility for Microsoft Windows (prior to Vista) which can quickly alter TCP performance parameters in the registry.
• Information on 'Tweaking' your TCP stack, Broadband Reports
• TCP/IP Analyzer, speedguide.net
• NTTTCP Network Performance Test Tool, Microsoft Windows Server Performance Team Blog
• Best Practices for TCP Optimization - ExtraHop