Thanks for sharing this wonderful article and this useful information. I see two issues, when l2nd driver was link down. Thanks for this very informative article. It did helped me a lot of our iSCSI solution. Much appreciated. And we'r in october Executive summary for Windows R2 and Broadcom multifunction adapters: 1. TCP offload - problems. Not OK for production use. Lot of time passed since the last blog. Still, no good news about Windows but today that is an OS of the past.
Processor performance impact was not measured - of course the more offloads the less loaded processor, but the goal of this test was to measure througputs and stability. Equipment was the same as used for W tests described in previous post. The lab test environment configuration is here click for full sized picture : Test No.
Customers must be adviced to use W R2 or W, otherwise they will loose their data. Only Qlogic are stable under W In the FAQ it is stated that this is a Flex limitation that is not yet addressed in firmware. This needs to be solved. This is a performance problem that needs to be solved.
Microsoft Data Protection server for example never finishes backup jobs in this configuration as it probably uses blocks greater than Note: Flex10 traffic limiter configured at 1Gbps allows at least 1. Not a problem at all for production, just a note. Test No. Traffic becomes very unstable. For more information, see Powercfg Command-Line Options.
This setting does not work properly if the system BIOS has been set to disable operating system control of power management. Enable static offloads. If the traffic is multi-streamed, such as when receiving high-volume multicast traffic, enable RSS. Disable the Interrupt Moderation setting for network card drivers that require the lowest possible latency.
Remember, this configuration 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. 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. The operating system cannot control SMIs because the logical processor is running in a special maintenance mode, which prevents operating system intervention.
In earlier versions of Windows, the Windows network stack used a fixed-size receive window 65, 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:. 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. 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. You may experience an issue in which the network device is not compliant with the TCP window scale option , as defined in RFC and, therefore, doesn't support the scale factor.
In such cases, refer to this KB , Network connectivity fails when you try to use Windows Vista behind a firewall device or contact the Support team for your network device vendor. You can use either netsh commands or Windows PowerShell cmdlets to review or modify the TCP receive window autotuning level. Unlike in versions of Windows that pre-date Windows 10 or Windows Server , you can no longer use the registry to configure the TCP receive window size.
For more information about the deprecated settings, see Deprecated TCP parameters. For detailed information about the available autotuning levels, see Autotuning levels. This was completely surprising because this customer was using SQL Authentication. That is a highly optimized query which should never have performance issues. The next thing to check was for filter drivers that might have inserted themselves in the TCP stack — antivirus, firewall, NIC teaming, etc.
Unfortunately, nothing like this was installed so there were no clues there. We disabled all of the Offloading settings, clicked OK and performance was back to normal. Connections were fast and query results were returning right after SQL Server generated them. In a less critical issue, it would be worth doing each setting one at a time and testing in between. In addition, I would also recommend that you go back after the fact and test enabling each setting to see if there is a negative impact.
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